GAS CHROMATOGRAPHY of METAL HALIDES Abstract Approved Ro Essor

AN ABSTRACT OF THE THESIS OF

James Eugene Dennison for the Ph. D. in Chemistry (Name) (Degree) (Major)

Date thesis is presented August 31, 1965 Title GAS CHROMATOGRAPHY OF METAL HALIDES Abstract approved ro essor

An all -glass gas chromatograph was developed for the analysis of corrosive metal halides. Included in the apparatus is a new liquid sampling system designed for fast repetitive sampling of corrosive liquids in an inert atmosphere. A flame photometer detector was developed to permit the detection of corrosive solutes in the gas stream without exposing the sensing element to chemical attack. Several materials were evaluated to determine their applicability as column materials for the analysis of metal chlorides. All the materials failed to separate the metal chlorides completely, except for Halocarbon 6 -00. However, polytetrafluoroethylene, FX -45 and Teflon, gave promising results. Chromatograms of metal chlorides on porous glass showed an inordinate amount of tailing. Nio- bium pentachloride and niobium oxytrichloride failed to elute from a column where a LiCl -KC1 eutectic was used as a liquid phase, except when the temperature was very high and the column very short.

1 Halocarbon 6 -00 on Chromosorb W was used to separate mixtures of metal chlorides. Several metal chlorides, including GeC14,

SnC14, AsC13 and TiC14 gave almost symmetrical peaks. No evidence of reactions between the metal chlorides and the column materials was observed, even at temperatures up to 185C. Log V versus g 1/T plots give straight lines for the four metal chlorides listed above, indicating a normal distribution between the stationary and mobile phases.

The reproducibility of peak areas for samples of AsC13 and

SnC14 was very good. Three mixtures of AsC13 and SnC14 were analyzed and the results are also considered to be quite good.

Chromatograms of a mixture of AsBr3 and AsC13 indicate that an exchange may take place between the two compounds. The same results were obtained for a mixture of SnC14 and SnBr4. GAS CHROMATOGRAPHY OF METAL HALIDES

JAMES EUGENE DENNISON

A THESIS

submitted to

OREGON STATE UNIVERSITY

in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

June 1966 APPROVED:

In Charge of Major

Chairman of Department of Chemistry

Dean o ra uate School

Date thesis is presented August 31, 1965 Typed by Marion F. Palmateer DEDICATION

To my wife, Helen, whose loyalty and understanding permitted the completion of this work. ACKNOWLEDGMENT

I wish to express my sincere gratitude to Dr. Harry Freund for his advice and encouragement during the investigations described in this thesis. I also wish to thank the Wah Chang Corporation for their partial support during the course of this investigation. IV III V II I BIBLIOGRAPHY CONCLUSIONS OF INVESTIGATION APPARATUS HISTORICAL INTRODUCTION METAL I G. F. E. D. C. B. A. H. G. F. E. D. C. A. B. . xpenm Metal Investigation Chlorides Agent Investigation the Investigation Chlorides Solid Investigation tography as Investigation Metal Investigation Solid Chlorides Detector Evaluation for Evaluation Thermal Flame Glass Solid Liquid Carrier Heating Flash HALIDES the Gas the in for Sampling Bromides for Chlorides Column Columns Vaporizer Photometer Sampling Analysis TABLE OF Chromatography the Oven Gas of the for Conductivity the of of THE Gas Metal Gas Gas of of of of of of Supply Gas an the Material System OF the Halocarbon NaCl FX Fluoropak Unfused Chromatography on GAS All of -solid System Chromatography Flame Chromotography Chlorides -45 Metal CONTENTS Halocarbon Gas Detector - -glass and CHROMATOGRAPHY and Detector as Chromatography Chromatography for Pretreatment Vycor Photometer of LiCl Chlorides a 80 Thermal Metal Partition the 6 -00 as -KC1 as 6 Gas -00. an as of Chlorides an of of Active Eutectic a Metal Chroma- Conductivity Detector Active Metal Agent Metal Partition of of for Page 87 83 78 66 63 57 53 46 41 34 34 31 27 24 22 18 17 15 11 11 3 1 LIST OF FIGURES Figure Page

1 Schematic diagram of an all -glass gas chromatograph for corrosive compounds 12

2 Heating oven and flame photometer detector 14

3 Liquid sampling system 19

4 Solid sampling system 23

5 Arrangement of columns and detector 25

6 Burner for flame photometer detector 28

7 Schematic diagram of the recording and integrating components for the detectors 30

8 Thermal conductivity cell 32

9 Response of flame photometer to various sample sizes 39

10 Chromatograms of NbC15 and NbC13 on glass beads, 40 11 Chromatograms showing the response of the thermal conductive detector to NbC15 and NbOC13 45 12 Chromatographic separation of petroleum ether, CC14, benzene and toluene on crushed unfused Vycor 49

13 The effect of sample size on the retention time 50

14 Chromatograms of SnCI , 4 GeC14 and SbC15 on porous glass 52

15 Chromatograms of ethyl acetate and SnCI on 4 Fluoropak 80 60

16 Ch.r om atog r am s of SbC15 on Fluoropak 80 61 5 Figure Page

17 Chromatograms of NbC15 and NbOC13 on Fluoropak 80 62

18 SnC14 and AsC13 on FX -45 65

19 Chromatographic separation of GeC14, SnCl4 and AsC13 68

20 Gas chromatographic separation of CC14, SnC14, AsC13 and TiC14 69

21 Calibration plot of AsC13 and SnC14 on Halocarbon 6 -00 73

22 Log V as a function of 1/T for inorganic chlorides 77 g 23 Chromatograms of SnC14 and SnBr4 on Halocarbon6 -00 80

24 Chromatograms of AsC1 and AsBr on 3 3 Halocarbon 6 -00 81 LIST OF TABLES Table Page

I HETP Values of CC14, AsC13 and SnC14 at Various 4 3 4 Temperatures 71

II Calibration of Peak Areas for AsC13 and SnC14 74

III Analysis of SnC14 /AsC13 Mixtures 75

IV Heats of Solution and Vaporization of Metal Chlorides 76 GAS CHROMATOGRAPHY OF METAL HALIDES

INTRODUCTION

In the metallurgical industry: quite often the purification process

depends on the distillation of the metal as the chloride, to separate the

metal from bulk impurities and other metals. If the <, mé t a l c h to - ride is free of contaminants, the metal, after reduction, will be pure otherwise any contamination may be reduced with the metal

causing the final product to be unacceptable. The appeal of in -line methods for analysis of the gaseous chlorination products is obvious, because immediate, accurate and continuous methods of analysis afford a tremendous saving in time, effort and money. In some cases oxychloride salts of metals exist as impurities in the stream of gaseous metal chlorides. The removal of oxygen from the stream will determine whether the finished product will have the desired qualities.

The applicability of gas chromatographic analysis to the gaseous chlorination products depends on developing compatible materials of construction and stationary phases, since the gaseous metal chlorides are quite corrosive at the temperatures required to keep them in the vapor state. If analysis can be made by gas chromatography, and adapted for in -line analysis, an important step will 2 have been made in the realm of metallurgical analysis.

The purpose of the work presented herein is to further the development of gas chromatography of metal halides by 1. extending the development of the apparatus required for handling and analyzing of corrosive chemicals at high temperatures,

2. developing sampling systems for corrosive liquids and solids in inert atmospheres, 3. evaluating liquid and solid materials for their applicability as column materials in the analysis of metal halides,

4. determining the applicability of gas chromatography to the analysis of specific metal halides. 3

HISTORICAL

The extension of gas chromatography into the field of inorganic chemistry was seen as a logical consequence as early as 1956 (57). Since then publications dealing with many different inorganic compounds have appeared. However, the number of publications or the number of inorganic compounds analyzed has not reached the propor- tion expected (77 ). Tadmor (77) suggests that the reasons for the limited application of gas chromatography to inorganic chemistry are that (1) there is a lack of an immediate, pressing need for new methods of analysis and (2) the corrosive nature of inorganic compounds render the application of gas chromatography to their analysis more difficult.

Most of the publications that have appeared have dealt with the separation and analysis of non -corrosive permanent gases and liquids, a more direct extension of gas chromatography since existing com- mercial instruments are usable without extensive modifications. There have been fewer applications to corrosive compounds. Several distinct areas exist where both interesting and useful work has evolved.

One of these is in the separation and analysis of metal chelates. So far the work has mainly involved metal complexes of acetylacetonates and more volatile trifluoroacetylacetonates and 4

hexafluoroacetylacetonates. Bierman and Gesser ( 4 ) have found

that many metals form stable complexes with acetylacetonates, and they were able to use gas chromatography for the separation of ace-

tylacetonate complexes of chromium, aluminum and berylium. A

column of Apiezon L grease (0.5 "`percent) on glass beads was used at 170 °Cfor the separation. Other normally stable metal complexes decomposed at temperatures where their vapor pressures were high enough for gas chromatographic separation. Trifluoroacetylacetonate and hexafluoroacetylacetonate complexes are more volatile and currently are being employed to extend gas chromatography to other metals. Ross (72) and Sievers, Moshier and Morris (74) have with some success studied the applicability of these ligands to the analysis of metals.

Gas chromatography has been extended to the analysis of phosphorous compounds by Shipotofsky and Moser (73) using a column of Kel -F 90 (ten percent) on Fluoropak 80. An all -glass system with a thermal conductivity detector was used to analyze mixtures of PC13, PSC13 and POC13. Good quantitative results were obtained.

Phosphorous pentachloride failed to elute from the columnand a yellow deposit inside the detector cell was observed, indicating that PC15 had decomposed or reacted with the system.

Metal chlorides are sufficiently volatile to be considered for gas chromatographic analysis. Keller (46) lists 20 metal chlorides 5 having boiling points below 350 °C. Furthermore, the chlorides of many metals are easily formed and are quite stable in the vapor phase. Metallurgical processes often take advantage of the volatility of metal chlorides as a means of separating the metals from bulk impurities and other metals (58).

Stationary phases widely used in the analysis of organic compounds have been employed for separations of metal chlorides.

Freiser (30) was able to resolve a mixture of SnC14 and TiC14 on a column of hexadecane (31 percent) on Chromosorb at 102 °C. The peaks were reported to be symmetrical and well defined.

Keller (46) separated SnC14, TiC14, TaC15 and NbC15 at 200 °C on a column of squalane (34.4 percent) on Chromosorb P. Chromato- grams of SnC14 and TiC14 were also obtained at 100 °C on a column of paraffin wax (38. 1 percent). Attempts to use silicone grease and

Apiezon T as liquid phases for the gas chromatography of SnC14 and TiC14 failed, except in the case of SnC14 on silicone grease, because of chemical reactions of the solutes and the system. Keller concludes that saturated hydrocarbons can be used for the chromatography of metal chlorides but that Apiezon and silicone grease cannot. Titanium tetrachloride chromatograms have a "foot" preceeding the primary peak. This "foot" is larger when the flow rate is slow, causing Keller to attribute the increase in size to an increased op- portunity for reacting with the column. It should be noted that 200 °C 6

is higher than the recommended temperature for the use of squalane in gas chromatographic work. The fact that Keller considers the

chromatograms of metal halides on squalane or paraffin, as de-

scribed, satisfactory is a testament to the difficulty of obtaining good

analyses while working in this field.

Wachi (80) reported the failure of SnC14 and TiC14 to come off

columns of silicone grease and Apiezon M grease supported on fire-

brick. Ferric chloride, not surprisingly, also failed to be eluted

from either of these columns at 3a5° C. The failure of organic stationary phases caused Wachi to shift to inorganic eutectics as stationary phases. Inorganic chloride eutectics have certain advantages over conventional partitioning solvents, namely, they are usually stable, have low vapor pressures and are not especially reactive.

Wachi (80) obtained chromatograms of SnC14 on a CdC12 -KC1

eutectic (41 percent) at 464°C, SnC14 on a A1C13 -NaC1 eutectic at

143°C. He obtained partial separations of a SbC13 -SnCl4 mixture on

the CdC12 -KC1 eutectic at 474°C and a SnC14 -TiC14 mixture on the A1C13 -NaC1 eutectic at 145°C. In all cases the solid support was

crushed firebrick. In general, these chromatograms show a considerable amount of tailing.

Euston and Martin (26)were able to obtain chromatograms of

several metal chlorides on a novel high temperature gas chromatograph. They noted that although individual samples of SnC14 and 7

FeCl3 gave satisfactory chromatograms on a column of CdC12 (50

percent) on Chromosorb, mixtures of the two completely failed.

They attribute the failure to a chemical reaction between the solutes.

A separation of a SbC13 -TiC14 mixture at 240 ®C on a column

of BiC13 -PbC12 eutectic (70 percent) was reported by Juvet and Wachi (45). Tadmor (79) has obtained numerous chromatograms of

metal halides, using an all -glass apparatus with a radio -activity de-

tector. He has also completed an excellent review (77) recently covering the gas chromatography of inorganic chemistry, including metal halides.

None of the work with metal halides has been quantitative. In

fact, the number of well formed peaks published so far has been

limited. Tadmor (79) was able to get a maximum recovery of 78 percent, and the recovery was sometimes below five percent. Since many volatile inorganic compounds are strong oxidizing

agents, they impose a severe limitation on the materials that may be used in the construction of gas chromatographs with which they are to be resolved. Efforts to overcome this limitation have generally

led to the utilization of all -glass systems, and to the use of other non -reactive materials.

An all -glass system for gas chromatography was first de-

scribed by Keppler, Dijkstra and Schols (48) for operation at high temperatures. Significant improvements made by Dal Nogare and 8

Safranski (15) have led to the use of all -glass gas chromatographs for separations and analyses of corrosive gases (73, 79, 80) and non- volatile compounds at high temperatures (12, 22, 48, 50). Most of the all -glass systems have employed thermal conductivity detectors equipped with hot wire filaments. The filaments have either been made of platinum (12, 16, 48), tungsten (22, 29) or tantalum (73).

Flame photometry was first used by Grant (33) for the detection of solutes in gas chromatography. The sensitivity was reported to be ten times as high as for thermal conductivity detectors. The sensitivity depends on the solute, of course, since a flame photometer detector is totally insensitive to many substances. Juvet and Durbin (44) used a flame photometer in the analysis of metal complexes of acetylacetónates.. Monkman and Dubois (61) developed a novel flame photometer detector for the analysis of halogenated hydrocarbons in the presence of other solutes, thus taking advantage of the selectivity of this detector. In general, factors applying to flame photometry apply also to flame photometer detectors, but with the chromatographic process, a powerful new dimension is added to the analysis. Ellis, Forrest and Allen (24) have found that the only materials. compatible with corrosive inorganic gases, i.?e. , C1F, C12, etc. , are Monel and nickel metals, polytetrafluoroethylene and polychlorotrifluoroethylene. These materials have been used at temperatures 9

up to 60°C in the analysis of fluorine containing gases.

Glass is known to be resistant to the attack of most compounds, except fluorine and strong bases. Therefore, the use of glass for the construction of gas chromatographs, including detectors, is not surprising. Glass beads have been useful, also, as the solid support

for theoretical or comparative purposes (14. 52, 63).

Glass microbeads have low surface areas, compared to most solid support materials, limiting their usefulness in gas chromatog-

raphy. Porous glass, made by crushing unfused Vycor (Code 7930), has a surface area larger than Chromosorb of corresponding mesh

sizes, and has been used in gas chromatography with interesting re-

sults. Rogers and Spitzer (71) found that when porous glass and diatomaceous earth had undergone identical treatments, they gave entirely different results when these two packing materials were used

for gas chromatography of hydrocarbons, with the retention on porous glass much greater. They also report that certain compounds, ketones, ethers, etc. , seemed to "disappear" in the chromatographic column. MacDonell, Noonan and Williams (56) studied the effect of deactivating the active sites on the glass that cause excessive tailing of the peaks.

Inorganic salts have found wide applications as active solids, liquid phases and solid supports. DeBoer (17) was able to separate metallic zinc and cadmium on sea sand coated with lithium chloride. 10

Hudson, Soloman and Doss (40) showed that inorganic salts could be used for the separation of polyphenyls at temperatures up to 500°C.

Details of the use of 21 different salts all coated on Chromosorb P are given. Lithium chloride gave the best results. Sodium chloride has been used as a solid support for organic liquid phases in several special applications (13, 36). The advantages of gas - liquid chromatography over gas -solid chromatography have led to the use of inorganic salt eutectics. These have been mentioned previously.

Kirkland (49) has published a detailed investigation of Teflon six and Fluoropak 80, in comparison with other materials, with regard to their applicability as solid support materials in gas chromatography. He concludes that although Teflon six poses some difficulty in handling, its advantage in many applications make its use quite attractive, especially for the chromatography of polar materials.

Staszewski and Janak (76) found that porous Teflon, compared to such solid support materials as Sterchamol, Celite, NaC1 and Ca3 (PO4)2, gave the lowest peak asymmetry, either when coated or uncoated.

Phillips and Owens (67) used Teflon capillary tubing, coated with Kel -F oils, for the analysis of corrosive gases. The use of polytetrafluoroethylene (PTFE) as the liquid phase in gas - liquid chromatography has not been published to date. 11

APPARATUS

An all -glass chromatograph was constructed for the gas

chromatography of corrosive metal halides. The unit was constructed entirely of borosilicate glass (Pyrex), with the exception of the platinum filaments of the thermal conductivity cells, from the sample

inlet to the point at which the gases escape to the atmosphere. The metal halides involved in this investigation are known to be unreactive to glass, so chemical reactions between the solutes and the gas

chromatograph is limited to the material making up the chromatographic column.

A schematic of the gas chromatograph is shown in Figure 1. All connections, whenever possible, are made by fusing the glass parts together in a permanent weld. Glass to metal seals are made using Teflon ferrules. Other connections are made using polyethyl-

ene unions. The components of the gas chromatograph are described in detail below.

Heating Oven

The heating oven is very similar to the one described by Wachi

(80). It consists of a heated aluminum cylinder within a larger cyl-

inder. It is insulated with high temperature insulating cement (AP. Green Fire Brick Company, Mexico, Mo.) and expanded vermiculite. A cylinder five and one -half inches in diameter and eight inches high, Metering valve Flash vaporizer E-- Sampling system Pre heater 3 -way Teflon column y_ Chromatographic column stopcock \ ------

I Flowmeter---. 11

Pressure Reference reduction column Vent valve Flame E- Photometer Detector r Mercury Oven boundary Helium - manometer Vent Supply CarrierI gas pretreatment Thermal Conductivity Detector

Figure 1. Schematic diagram of am all -glass chromatograph for corrosive compounds.

tv 13

with lids machined from one -quarter inch aluminum plate to fit

smugly over the ends, forms the inner casing. To insulate the metal .

cylinder from the heating wire, the cylinder is wrapped with a single layer of asbestos sheet, then impregnated and covered with a thin

coat of furnace cement. When dry, the cement forms a thin but

rigid electrical insulation and yet is but a mild thermal shield.

Heating elements, made from 28 AWG nichrome wire, are wound around the cylinder evenly in a double helix configuration to give a uniform heating envelope for the chromatographic columns and detector. Each heating element is 20 feet long. Insulated binding posts are used to anchor the ends of the heating wires. Connections to the heating elements are made with high temperature cable. The maximum power dissipated by each element is 165 watts. A layer of asbestos sheet is used to cover the heating wires to hold them in place and to protect them from inadvertent shorting.

The inner casing is placed in a larger aluminum cylinder, 12 inches in diameter and 14 inches high as shown in Figure 2. Ver- miculite is used to insulate around the heating elements to permit easy access for inspection and repair. For the insulation at the top and bottom, as indicated, the high temperature insulating cement is used. A removable plug is cut in the insulating cement at the top for access to the oven compartment. A slit, cut in the insulating cement, provides for the connection to the sample inlet. Second slit Filter Collimating tube Glass chimney Flame First slit Aluminum detector block Photomultiplier tube Insulating Ii cement Well for cartridge heater

Inner casing Vermiculite Heating oven

Outer casing

Insulating cement

Figure 2. Heating oven and flame photometer detector. 15

Power to the heating elements is provided by two autotrans-

formers (Superior Electric Company, Bristol, Conn. ). One gives

a variable but continuous power input to the oven and is manually

reset when a temperature change is desired. The other transformer

is wired to give "high -low" input as described by Euston and Martin

(26). A temperature controller (Minneapolis -Honeywell Regulator

Company, Minneapolis, Minn. ) is used to operate the "high -low"

switch which controls the power input to the second heating element.

Thus, temperature control within + 1 °C or better is possible within

the range of ambient to 500°C or higher, i. e. , the softening point of

aluminum. In actual practice the oven has been operated up to 480° C with no difficulty. When the oven is allowed to stabilize for several hours, the temperature change within the period of a chromatogram is usually undetectable.

Carrier Gas Supply and Pretreatment

Helium is used as the carrier gas in all experiments. When the thermal conductivity detector is used, the carrier gas stream is split as shown in Figure 1, and passes through parallel chromatographic and reference columns and thermal conductivity cells. Otherwise, only one stream of helium is required.

Gas Flow Measurement and Control. Regulation of the pressure 16 and control of the flow of carrier gas are achieved with a diaphragm reducing valve ( The Matheson Company, East Rutherford, N. J.) fitted to a cylinder of helium (Chematron Corporation, Chicago, Illinois). The reducing valves regulate the pressure, thus providing the desired flow rate to chromatographic and reference columns.

The gas flow through the reference column is regulated with a Nupro fine metering valve (Nuclear Products Company, Cleveland, Ohio). A floating ball rotameter (The Matheson Company, East Rutherford,

N. J.) with a precision bore tube (size R -2 -15 AAA) is used to moni- tor the flow rate of the carrier gas. Whenever a new column is in- stalled, or the gas chromatograph is operated at a new temperature, the rotameter is calibrated with a soap bubble flowmeter attached to the exhaust vent. The calibration of the rotameter is checked periodically. It is not possible to measure the flow rate of the carrier gas with the soap bubble flowmeter when the flame photometer is in operation because the exit of the gas stream is located inside the flame of the flame photometer burner. A mercury manometer is connected to the carrier gas stream through a Teflon stopcock to provide a means of measuring the inlet pressure of the carrier gas. There is a very small pressure drop across the Linde Molecu- lar Sieve column, which helps to damp out fluctuations in the flow rate of the carrier gas. 17

Carrier Gas Pretreatment. The carrier gas passes through a

column of Linde Molecular Sieve 5A, activated by heating under vacuum for four hours at 400°C, to remove the water from the gas

stream. In early work fine copper wire and zirconium granules,

heated to 600° C - 700° C, was used to remove both water and oxygen from the stream. Subsequently it was found that oxygen in the carrier gas stream causes no difficulty. Therefore, molecular sieve is used because it is easier to regenerate.

Carrier Gas Preheater. The carrier gas is preheated by passing through a coiled glass column (four feet long and six millimeters

outside diameter) within the heating oven, as shown in Figures 1 and

5. At normal flow rates, 25 milliliters per minute to 120 milliliters per minute, the residence time of the gas in the preheater is between 0. 95 to 0. 2 minutes, and is sufficient to bring the temperature of the gas up to the temperature of the oven. The heated gas then passes into the flash vaporizer of the sample inlet system. The re- quirement of rapid vaporization is met by the combined use of the carrier gas preheater and the flash vaporizer.

Flash Vaporizer

A flash vaporizer is constructed by winding 30 AWG nichrome wire, seven feet long, around a section of the glass tubing carrying 18 the carrier gas. The position of the flash vaporizer relative to the

sample inlet is shown in Figures 1 and 3. The wire is insulated and held in place by a coat of ceramic cement, Insulate No. 1 ( Saureisen

Cements Company, Pittsburgh, Penn. ). The glass tubing is previously covered by a thin coat of paraffin to prevent the cement from becoming bonded to the glass. An autotransformer provides the power required to control the temperature within the glass tubing.

Temperatures up to 500° C have been attained.

Liquid Sampling System

The sampling systems are designed to permit repetitive sampling in an inert atmosphere. The introduction of solute samples into the chromatograph is the most difficult and crucial operation in the chromatographic process. Because the metal chlorides are reactive, ordinary needles plug very easily and any reaction with the sampling system renders reproducible analysis of mixtures impossible. For those reasons a Teflon needle is used for the injection of the liquid samples into the sample inlet. The needle is 0. 013 inches in diameter and is eight inches long. A Kel -F hub (Kellog Corpora- tion, Jersey City, N. J. ) connects the Teflon needle to the 10 111 syringe (The Hamilton Company, Whittier, Calif. ).

The sampling chamber (Figure 3) is made by attaching a screw - cap culture tube to a three -way Teflon stopcock, which in turn is Entrance to oven 2mm Pyrex Flash Culture tube Sampling valve Culture tube capillary vaporizer screw cap Culture 3 -way Teflon screw cap tubing + tube I ll stopcock I /1111 /I // Helium in / i VINEt `` Li rirlra' Column Flanged 2mm Silicone capillary Si icone Culture rubber tubing rubber tube Glass wool plug septum septum water To Teflon cooling variable needle jacket transformer entrance Beginning Nichrome of column X V- heating wire i Pressure equalization valve 3 -way Teflon stopcock

.0 Figure 3. Liquid Sampling System 20

attached through the other arms to the sample inlet and to the sample

holder. The sample holder is not shown in Figure 3, since Figure 3 only gives the top view of the sampling chamber. Sample holders are mady by sealing one end of 12/5 glass socket joints. The connection to the sample chamber is made through the corresponding ball joint which is sealed to one of the arms of the stopcock. Kel -F 90 stopcock grease is used to grease the ball and socket joints and the stop- cocks.

The sampling chamber is attached to the sample inlet of the column as shown in Figure 3. The silicone rubber septums (DuPont

SR 5550) are replaced about once per week or as necessary. A water -cooled jacket is incorporated into the sample inlet system to provide a sharp temperature change at the point where the Teflon needle enters the flash vaporizer, in order to prevent premature vaporization of the sample. Capillary tubing, placed inside each of the culture tubes, prevents the Teflon needle from buckling as it is being pushed in through the rubber septum.

With the arrangement described, it is possible to replace the sample chamber with a simple screw cap equipped with a septum, and then make injections of non -corrosive solutes with an ordinary syringe. The syringe must be equipped with a needle at least four inches long in order to inject the solute in the carrier gas stream at the beginning of the chromatographic column. The reproducibility 21

of peaks obtained by the direct injection of the solutes into the gas stream is somewhat better than when Teflon needles with larger bores are used.

The sample chamber is taken into an inert atmosphere to at- tach the sample holder containing the corrosive metal chloride. To inject samples of corrosive materials into the gas chromatograph, a 10 µl syringe with the Teflon needle is filled to within one - fourth inch of the end of the needle with CC14 and threaded through the stopcock into the sample holder. The pressure equalization valve must be opened to ensure that the pressure in the sample holder is equal to the inlet pressure of the chromatographic column. The needle is immersed into the liquid and a measured quantity of liquid drawn into the needle. The needle is withdrawn and rethreaded through the stopcock, after the stopcock has been rotated 180°, and into the sample inlet. The solute is then injected into the carrier gas stream. A quantity of CC14 is injected along with the sample to flush the sample into the gas stream. The volume of a Teflon needle is large compared to a normal syringe needle. A four microliter liquid sample is 3. 5 centimeters long in a Teflon needle (O. 013 inches diameter) that is eight inches long. Therefore, a normal injection of the liquid is impossible. An air column between the solute liquid and CC14 displaces the sample into the chromatograph when the injection is made. If a small quantity of CC14 is not injected also, small droplets of the solute liquid 22 remain inside the Teflon needle, causing a five to ten percent error in the sample size. Furthermore, the error is not absolutely reproducible. The flushing technique averts this error.

Solid Sampling System

The solid sampling system is also designed to permit repetitive

samples to be introduced into the chromatograph in an inert atmosphere. The physical construction is similar to that of the liquid sampling system, although its operation is simpler. The solid sampler chamber and sample holder is shown in Figure 4.

The sample holder is a 125 x 15 screw -cap culture tube that has a small delivery tube (four millimeters outside diameter) attached to the bottom. A glass rod serves as a plunger to force some of the solid sample out through the delivery tube. In operation, the delivery tube of the sample holder is inserted into the sample chamber through the silicone rubber septum as shown. A glass rod with a small glass boat on the end enters through the rubber septum shown on the end of the sample chamber, at 90° to the delivery tube. Thus the solid sample may be forced out through the delivery tube by the glass plunger, and into the glass boat. Subsequently, the Teflon stopcock is opened and the boat is pushed into the sample inlet where the sample evaporates and is carried into the column. The glass boat is then retracted and the stopcock is closed. The sample Flash vaporizer Culture tube Teflon stopcock Septum screw cap 1riiimill He

1 i1111N111.

Culture tube Glass wool Septum Culture tube screw cap plug screw cap Septum

Sample holder delivery tube C J entrance

Plunger Sample holder Delivery tube Entrance for glass rod and boat

Figure 4. Solid sampling system. 24

holder is partially filled and the delivery tube is inserted into the

sample chamber in an inert atmosphere to prevent contamination of the sample.

All septums are made of silicone rubber (DuPont 5550). They are replaced as necessary.

The bore of the Teflon stopcock was enlarged to accomodate the glass boat and rod. The inlet system is capable of withstanding positive pressures up to 40 PSI.

Glass Columns

When only the flame photometer detector was being used, re- quiring no reference column, the chromatographic column was slipped over the carrier gas preheater column and attached by one end to the flash vaporizer. The other end was attached to the exhaust vent tube leading to the burner of the flame photometer. All columns and the detector were fastened to the top of the oven so that they could be inspected before being placed in the heating oven.

Later development of the thermal conductivity detector made an additional glass coil for the reference column necessary. Also required was a detector block, or heat sink. The final arrangement is shown in Figure 5. Thus the carrier gas stream passes from the chromatographic column, through the conductivity cell and into the flame of the flame photometer (not shown in Figure 5). 25

Connections for TC cells 1111 Exhaust vent

1Ìr In 11111111111111111 I111IIEiùai Pt -glass seal Flash vaporizer Oven lid Glass supports for Pt leads

Aluminum block Thermocouple - well TC cells

Sample 110) loll carrier gas Carrier gas stream preheater coil Reference 1 carrier gas stream Chromatographic column coil (5 mm o. d.)

Reference column coil ( (6 mm o. d.)

Figure 5. Arrangement of Columns and Detector 26

Both the preheater column and reference column are perma-

nently assembled as shown in Figure 5. The reference column is filled with Chromosorb P to provide a convenient pressure drop for the regulation of the flow of the reference gas stream.

Coiled glass columns are made by the method described by Wachi (80). Glass tubing (five or six millimeters outside diameter)

is wound around a section of large glass tubing. The large glass tubing, either two and one -half or three inches in diameter, depending on the diameter of the coil desired, is insulated by a triple layer of asbestos.. Coils up to 24 feet in length have been made.

The chromatographic columns are connected to the thermal conductivity cell and the flash vaporizer before they are filled with the packing material. To fill the column, the packing material is fed into the front end of the column through a section of rubber tubing at-

tached to a glass funnel. A vacuum line is attached to the column exit. A Vibra -tool (Burgess Vibracrafters, Incorporated, Grayslake,

Ill. ) is used to pack the material in the column. Glass wool is used to plug both ends of the column. After the column is packed, the entire assembly is placed in the heating oven and the chromatographic and reference streams are connected by means of ball -and- socket joints, and the necessary electrical connections are made.

To precondition the column, a slow stream of helium (one to five milliliters per minute) is passed through the column for four hours 27 or more.

Flame Photometer Detector

In the early work involving an all -glass chromatograph, a flame photometer detector was developed to detect corrosive metal

chlorides, particularly NbC15 and NbOC13. The gases emerging

from the chromatographic column are passed directly into a flame

and the spectral emission detected by a photomultiplier tube. With

this arrangement the solutes never come into contact with any sub- stance other than glass and column packing materials. A small glass tube (three millimeters outside diameter) car- ries the solute from the chromatographic column through the lid of the oven, up through the center of the burner shown in Figure 6, to the base of the flame. Air and gas flows into the burner through the indicated entrances, and up along the barrel of the burner to the tip.

Each of the partitioning cylinders is machined from 316 stainless steel tubing to fit snugly, one within the other. Protrusions on the inner cylinders hold them concentrically within the outer cylinder to give a symmetrical flame. The various parts are silver - soldered together.

To prevent the condensation of the solutes in the exhaust vent, the burner is mounted in an aluminum block bolted to the top lid of the heating oven. Figure 2 illustrates the arrangement of the burner 28

Inner cylinder (3/16 inch o. d. ) Middle cylinder (1/4 inch o. d. ) Outer cylinder (5/16 inch o. d. )

Centering protrusions Barrel stock (5 /8 inch o. d. )

Gas inlet 4- Air inlet

Silver solder

1 Entrance for gas stream (3 mm o. d. glass tubing)

Figure 6. Burner for flame photometer detector. 29

and associated parts of the detector. A cartridge heater is mounted

in the aluminum block to maintain the temperature of the block

higher than the temperature of the oven. Back diffusion of water into

the exit tube is very small because of the high linear velocity of the

gas stream. Therefore, the formation and condensation of metal oxides within the exit tube is small, although the exit tube is re-

placed occasionally because of the buildup of oxides within the tube.

A glass chimney, 25 millimeters o. d. , is placed on top of the

aluminum block to avert the wavering of the flame. Light emitted by the flame passes through the glass chimney

and into the collimating tube as shown in Figure 2. An entrance slit is made by cementing razor blades with the sharp edges side -by -side, to the end of the collimating tube. The emitted light passes along

the tube, through the filter, through another slit and into the photo - multiplier tube (RCA 931 -A). Slits were used to reduce stray light

reflected along the collimating tube. The cathode of the photomultiplier tube is biased by 12 45 -volt storage batteries connected in series.

A schematic diagram of the photomultiplier tube is shown in Figure

7. In operation, the output voltage is fed into a Heath operational amplifier, operated as a follower, to isolate the high impedance photo - multiplier circuit from the low impedance recorder circuit. The input into the recorder is regulated by a sensitivity control and bias Balance control Photomultiplier tube . 46 ohm (10 turn) Bias control Brown 185 185 2. 5 mv J ohm ohm Recorder R=440K 10K 1 10K I 0 -500 ma TC TC 1.5v Sample 50 ohm 10 -turn Referenc cell Current Ì cell Adjust 540v-= T 10 ohm 6 volt S2 Philbrick UPA - 2 Integrator

R Current 2R limit Sensitivity Bausch and Lomb 2. 2 me adjust VOM Selector switch Sensitivity Recorder 5. 6 meg selector

Figure 7. Schematic diagram of the recording and integrating components for the detectors. 31

control. A bias control is required because a small residual back-

ground light entering the photomultiplier causes a voltage to enter

the operational amplifier, thus giving a small signal even when no

sample is passing through the flame. A bias voltage bucks out this

residual voltage. A Brown 2. 5 millivolt recorder is used to record the detector response. The drift caused by the Heath operational amplifier is negligible.

The output of the flame photometer detector is never integrated because the sampling of solid samples is not sufficiently quantitative to warrant integration of the peak areas.

Thermal Conductivity Detector

Thermal conductivity cells are constructed in the manner de-

scribed by Dal Nogare and Safranski (16). At first two -mil nickel filaments were used in the construction of thermal conductivity cells, but unsatisfactory electrical connections to the leads were never realized,

Figure 8 shows the construction of one of the thermal conductivity cells. These cells are made entirely of Pyrex, excepting the filaments and leads. Three -mil platinum wire, 30 inches long, is wound around a hypodermic needle and spot -welded to 30 AWG platinum leads. The leads are threaded through the glass supports and the filaments are sealed in position as shown in Figure 8. The 32

Platinum leads I 1 <---Exhaust vent (30 AWG) 1 1 1 1

1 1 i !! 1, r

1 Glass support for II Pt lead -Platinum filament 1111 3 mil I i 11 11 II II II é Pyrex glass (6 mm o. d.) 11 II 11 II Iv

Pyrex capillary (2 mm o. d.)

Carrier gas inlet

Figure 8. Thermal conductivity cell. 33 resistance of the cells so constructed is 14. 6 ohms at 20 °C. The thermal conductivity cells are incorporated into a Wheat- stone bridge as shown in Figure 7. Power to the bridge is supplied by a high- capacity storage battery. The current control and the current limiting resistor are conventional for thermal conductivity bridges. A selector switch is incorporated in the circuit to permit the selection of either detector. The bias control is not required when the thermal conductivity detector is used. For the integration of the peak areas a Philbrick UPA -2 chopper stabilized operational amplifier is used. The integral is recorded on a Bausch and Lomb VOM recorder equipped with an automatic reset. The latter consists of a sensitive microswitch mounted on the recorder in a position such that the contracts of the switch are closed when the pen has reached its maximum excursion. The microswitch discharges the integrating capacitor. 34

INVESTIGATION OF THE GAS CHROMATOGRAPHY OF METAL HALIDES

Evaluation of the Flame Photometer Detector for the Analysis of Metal Chlorides

Introduction. The evaluation of the flame photometer detector

consists of putting the detector into an operational situation, i. e. , using the detector to detect the components of a sample as they

emerge from the chromatographic column. In addition, the detector

is evaluated for long and short term drift, noise, sensitivity and the

effect of gas and air (oxygen) flow rates. Samples of NbC15 and Nb0C13 are used as the solutes in the evaluation.

Experimental. All of the components of the gas chromatograph

are described on pages 11 -33. The apparatus consists of the carrier gas supply and pretreatment, including drying train, preheater and flash vaporizer; the solid sampling system, chromatographic column flame photometer detector and heating oven.

The chromatographic column is filled and packed as described on page 26. Glass beads, 80 -120 mesh, are used to pack the column. The glass beads are acid -washed with concentrated nitric acid, fol- lowed by washing with concentrated hydrochloric acid, and are dried at 110°C.

Pure NbC15 was obtained from Wah Chang Corporation, Albany, 35

Oregon. For the preparation of NbOC13 a long glass tube (25 milli-

meters o. d. ) is fitted on each end with a one -hole rubber stopper. Fifty grams of NbC15 are placed in the glass tube about one foot from the end. Connections are made to a stream of helium so that

the helium passes through the tube containing the NbC15. The exit end of the tube is sealed from the atmosphere by bubbling the helium through a concentrated HZSO4 solution. The tubing holding the

NbC15 is placed in a combustion furnace and heated to 250 ®C.

The NbC15 is evaporated and carried to a cool part of the tube where it condenses. The helium stream is interrupted and air is allowed to leak into the tube, then the passage of helium through the

tube is continued and the distillation is repeated. When the conden-

sate of NbC15 /NbOC13 nears the end of the tube, the flow of helium

is merely reversed, care being taken to prevent the H2SO4 from

being drawn back into the tube. By leaking air into the tube and

distilling the mixture repeatedly, all of the NbC15 is converted to

NbOC13. Eventually, Nb2O3 is formed, indicating that no NbC15 re- mains, whereupon the tube is sealed on both ends and taken into an inert atmosphere where the NbOC13 is removed and placed in a polyethylene bottle. The bottle is sealed with paraffin. The flow of the air and gas streams into the flame photometer burner is controlled by a series pressure valve arrangement consisting of a diaphragm type reducing valve on the cylinder and a simple 36

screw clamp on the section of rubber hose leading to the burner. In the cases where line gas is used, no reducing valve is required.

Results and Discussion. The nomenclature recommended by Dal Nogare and Juvet (15) is used in the following and other discus- sions.

With the flame photometer detector in order to have an "air peak ", a volatile component known to have no retardation must be introduced into the gas stream. The component must give a spectral emission when it passes through the flame of the burner.

Other components or the empty boat on the glass rod give no recorder deflection.

It is not possible to obtain quantitative data on the sensitivity of the detector because the solid sampling system includes no pro- vision for weighing the solid samples. It is possible to find the conditions under which the operation of the detector is most satisfactory, i. e. greatest sensitivity and stability of the response.

With zero input into the operational amplifier (input grounded) the recorder trace is essentially noiseless and does not drift. When the detector is restored to its normal operational order, but no light is permitted to enter the photomultiplier tube housing, the recorder trace again shows no drift, and little noise. The noise is caused by electrical pickup (a. c. ) in the electrial wiring which is. necessarily 37

long. The wiring is shielded to reduce the a. c. pickup. With the detector completely restored to normal operating order, some noise and drift is normally present, depending on the conditions of the operation of the burner.

When a cylinder of propane is used to provide the fuel for the burner, a very noisy response on the recorder results, caused by an inadequate regulation of the fuel stream. Line gas, available in

the laboratory, requires no further regulation. The regulation of

the air stream is not as crucial; small variations in the flow rate

changes the sensitivity of detector and the position of the trace on the recorder very little.

Many metals, including niobium, have greater sensitivities in

spectrographic analysis when a reducing flame is used to excite the atoms to higher electronic states (32). This effect is attributed to

the fact that as oxides these metals are very difficult to excite, but when they are reduced to the atomic state, their excitation is much easier. In this work it is found that the greatest sensitivity occurs when a cool reducing flame is used, thus corroborating the conclusions advanced above.

Therefore, it is disadvantageous to use a stream of oxygen for the combusion of the fuel, not only because of the reduced sensitivity, but also because of the greater noise level caused by the greater emission of light from the hot flame. For routine operation a pale 38 blue flame, about one centimeter high, with no inner blue cone, is used.

The two slits in the light path and the filter are used to reduce the background noise, which otherwise is quite high under conditions of maximum sensitivity. The slits are effective in preventing the admission of stray reflected light into the photomultiplier tube. A green filter, Kodak No. 61 (Eastman Kodak Company, Rochester,

N. Y. ), having a minimum absorbance of 0. 40 at 520 mµ is used to filter out light below 480 mµ and above 580 mµ, yielding a more stable background.

Because of the lack of quantitative information on the size of the samples no accurate figure on the comparative sensitivity of the detector is available. In addition, the sensitivity varies greatly with the identity of the component, as it does in flame photometry.

The response of the flame photometer detector to samples of

NbC15 is shown in Figure 9. Because the size of the solute samples are relative only, Figure 9 shows qualitatively that the peak heights and peak areas are directly related to the sample size. In this case, the smallest peak shown in Figure 9 consists of a small amount of NbC15 powder, barely large enough to be seen with the naked eye.

Figure 10 shows three chromatograms of NbC15, NbOC13 and a mixture of the two compounds. In Curve A the slight bulge on the trailing edge indicates the possible presence of a small amount of 39

Oven temperature 340 °C Flash vaporizer 360 °C Input pressure 20 psi Flow rate 33 ml /min Column Glass bead 2.0 - 80 -120 mesh Sample size about 10 mg

° g

0. 5-

0 1.0 2.0 3.0 4.'0 5.0 Time (minutes) Figure 9. Response of flame photometer to various sample sizes. 40

A NbC15 Oven temperature 340 °C Flash 360 °C B NbC15 plus NbOC13 vaporizer Input pressure 20 psi 2. 0- C NbOC13 Flow rate 33 ml /min Column Glass bead 80 -120 mesh Sample size about 10 mg

1.5- A

o á

0. 5-

0 1 2 3 4 5 Time (minutes) Figure 10. Chromatograms of NbC15 and NbOC13 on glass beads. 41

NbOC13. The sample sizes were not equal. The flame photometer detector that has been developed has both advantages and disadvantages in its application to gas chromatography. It is insensitive to changes in temperature or flow rate and may be used at temperatures above the normal operating range of many other detectors. Its sensitivity to many substances is comparable to thermal conductivity detectors. And as mentioned, the use of materials of construction that react with the solutes, especially at high temperatures, is avoided.

On the other hand, the sensitivity changes with variations in the air and gas flow rates to the burner, and certain components may be undetectable because they emit no light in a flame.

The Evaluation of an All -glass Thermal Conductivity Detector for Gas Chromatography of Metal Chlorides

Introduction. Not all metals have strong emission lines within the sensitivity range of the flame photometer. In some cases this insensitivity may be advantageous, allowing one component to be re- vealed in the presence of others. Otherwise, if the detection of all components is required, a supplementary or replacement detector may be necessary, as in the present work.

All -glass thermal conductivity cells have been used for high temperature gas chromatography and for gas chromatography of corrosive materials by many workers, as mentioned previously. 42

The thermal conductivity cells used in this work are patterned after the design of Dal Nogare and Safranski (16).

Experimental. The apparatus used in Section IV A is modi- fied to include the thermal conductivity cells, a reference column and a detector heat sink. The description of these components is given on pages 11 -33. Although the flame photometer detector is not used, the burner provides a means of visually observing the appearance of the various components as they emerge from the column and pass through the flame.

Metallic nickel is unreactive toward chlorine and many chlorine compounds. Therefore, thermal conductivity cells were constructed in which nickel wire, 0. 002 inches in diameter, was used to make the filaments. The ends of the filaments were silver -soldered to platinum leads (30 AWG) which made electrical connection through the glass walls of the cells to the external arms of the thermal conductivity bridge.

Results and Discussion. The thermal conductivity cells with nickel filaments gave unsatisfactory performance because electrical connections between the nickel wire and the platinum leads were not made satisfactorily. After only one week, the detector failed because the silver solder had reacted with samples of NbC15. No attempt was made to spot -weld the nickel filaments to the leads in a 43 reducing or inert atmosphere because the satisfactory performance of platinum filaments obviated any further need of cells with nickel filaments.

Thermal conductivity cells made with three -mil platinum wire filaments have been used for several months with no evidence that the filaments have reacted with the solutes. The background noise is very low, less than one microvolt, at filament currents up to 150 ma and at temperatures up to 480°C. Changes in the temperature of the detector block of five degrees give a change in the recorder response of only 100 microvolts.

The sensitivity factor suggested by Dimbat, Porter and Stross (18) is 21 for a filament current of 100 ma. Arsenic trichloride was used for the calculation. The above figure for the sensitivity factor is small compared with many thermal conductivity detectors (200 or higher), but the value could be increased markedly by increasing the filament current.

Many TC cells have been constructed in which platinum filaments have been used in an otherwise all -glass system. Few have used coiled filaments. Dal Nogare and Juvet (15) have pointed out that little is gained by increasing the length of the filament in the detector since the voltage output is essentially independent of the filament length. However, it is easier to match the reference and sample filaments with longer filaments since a 0. 1 inch difference in 44 length of two filaments two inches long is five percent, but is only

0. 3 percent for filaments 30 inches long.

An "air peak" is always obtained when the thermal conductivity detector is used, especially when the solid sampling system is employed. An empty glass boat causes a deflection in the recorder trace because the cool boat, entering the carrier gas stream, cools the gas until the boat reaches the temperature of the stream. The cooler gas passes on through the column and causes the deflection on the recorder when it reaches the detector. Longer columns reduce the magnitude of the deflection, but the longest columns used (24 feet long) still gave a small deflection.

If an unretarded component is present in the sample, the "air peak" is larger. In Figure 11, a large "air peak" indicates the presence of a highly volatile component in the sample, probably HCl released by the reaction of an H2O impurity with NbC15 or NbOC13.

The unretarded component gives no emission as it passes through the flame of the burner.

In the comparison of the chromatograms in Figure 11, it is apparent that NbOC13 tails much more than NbC15.

Chromatogram D was obtained for a sample of NbCl5 at an oven temperature of 240°C. Otherwise, the conditions for all the chromatograms in the figure were identical. The maximum excursion of the detector pen is 0. 6 microvolts, resulting from an apparent > Figure Recorder response E 0. 1. 1. 2. 2. 0 5 0 5 0 5 1 0 - - 11. Column Filament Flow Detector Oven Flash Chromatograms to rate temperature vaporizer NbC15 packing current 1 and NbOC13 showing 2 75 33 320° 370° 300° ma mis Time C C C the /min C response 3 (minutes) of Shoulder the 4 thermal D C B A NbC15 Mixture NbOC13 NbC15 due to 5 conductive at NbOC13 of 240° NbC15 C D detector 6 and NbOC13 7 46

saturation of the carrier gas stream by the vapors of NbC15. Either smaller samples or higher temperatures are required. The adjusted retention volume of the solutes on glass beads is very small.

The Investigation of Unfused Vycor as an Active Solid for the Gas-solid Chromatography of Metal Chlorides

Introduction. Chromatograms of NbC15 and NbOCl3 on glass

beads, obtained in the course of the evaluation of the detectors, gave some promise that metal chlorides could be resolved on glass beads if a column with a sufficiently large number of theoretical plates could be prepared. The two obvious methods, namely, using longer columns, or glass beads of much smaller diameter, lead to excessive input pressures for reasonable flow rates. A suitable alterna- tive is to use a porous glass material with a high surface area. Unfired Vycor has a large surface area for a given particle size because of many micropores throughout the glass. MacDonell, Noonan and Williams (56) have prepared columns of porous glass, both coated and uncoated, for the separation of hydrocarbons at 125°C. They report that of all compounds examined, halogenated hydrocarbons are eluted most easily, and that the deactivation of the silanol groups greatly decreases the amount of tailing normally encountered.

The lack of chemisorption of halogenated hydrocarbons points to a 47 more nearly normal behavior of these compounds with respect to the glass. An investigation was launched to determine if the metal chlorides could be resolved using porous glass as an active solid or as a solid support.

Experimental. The apparatus in this experiment is identical to that described previously in Section IV B.

A chromatographic column is made by filling a Pyrex glass column, 16 feet long and six millimeters outside diameter, with crushed unfused Vycor, Code 7930 (Corning Glass Works, Corning,

N. Y. ). The packing material is reactivated by heating under vacuum to 400°C for four hours. T o deactivate the silanol groups, a slurry of the packing material in methanol is refluxed for 30 hours, as suggested by MacDonell, Noonan and Williams (56). The material is size graded to 50 -60 mesh to remove the fine particles formed in the deactivation process.

Results and Discussion. As expected, a great increase in retention times was realized when the glass bead column was replaced by one of porous glass. In fact, the adjusted retention volume for

CC14, nearly zero on a column of glass beads, is about 200 milliliters on a column of porous glass, at equivalent oven temperatures and carrier gas flow rates.

A separation of several hydrocarbons and CC14 is shown in 48

Figure 12. The wide range of boiling points for the components of the sample makes it not surprising that they are resolved. The components are eluted in the order of their boiling points, but since the retention times vary widely with the size of the samples, a correction to zero sample size must be made before any meaningful relative retention time data can be obtained. Toluene and benzene both show some tailing even at 180°C. At 140°C the tailing is quite severe for these two compounds, and even CC14 tails badly.

Figure 13 shows the effect of the sample size on the retention times for CC14 samples. An increase in the retention times for de- creasing sample sizes is opposite to the effect normally encountered. This behavior is explained by the nature of the adsorption of gases on substances having active sites. Small samples are retained longer because there are fewer molecules per active site. As the samples become larger there are more molecules per active site, and the solute is retained less. Since the number of active sites is constant for a given column, all samples should have coinciding trailing edges because all active sites are filled as the solute maximum passes, and as the solute concentration decreases, the elution of the molecules from the active sites becomes identical for all samples. This ex- planation is dependent on having the solute enter the chromatographic column in the vapor state. Figure v ó m 12. Recorder response 0. 1. 1.5 2. 0 5 0 0 crushed Chromatographic - .. - <4 H unfused 1 Vycor. 2 Petroleum ether separation 3 Tr of petroleum 4 q a) g N a) O Q) Time 5 Sample Flash Oven Input Flow Column (minutes) temperature vaporizer ether pressure rate 6 size CC14 H o (1) G a) 7 4 250' 180°C 70 30 Crushed , petroleum benzene µl benzene mis psi C of 8 16 /min unfused feet (30 and ether %) 9 long, toluene and Vycor (30 toluene 6 %), mm 10 on code CCl44(1 o. (30%) d. 7930 Oaf, ) Column Crushed unfused Vycor code 7930 16 feet long, 6 mm o. d. Input pressure 30 psi Flow rate 70 ml /min 2. 0 Oven temperature 180oC Flash vaporizer 250oC Sample size Various >

m 1. 5

ro 1. 0-

0. 5-

0 2 4 6 13i 1b Time (minutes) 01 Figure 13. The effect of sample size on the retention time. 0 51 Although refluxing the porous glass in methanol did reduce the tailing and improve the symmetry of the peaks, it is apparent that

active sites are still present. It is probable that some of the de-

activated silanol groups are restored when the temperature is raised to 190°C.

Chromatograms of other compounds, i. e. , GeC14, SnC14 and

SbC15, shown in Figure 14, indicate that the adsorption of the samples on the active sites is similar for all three compounds. Again, the trailing edges nearly coincide, although it is not as evident as it is for CC14 samples. For these metal chlorides the retention time varies widely with changes in the size of the samples. It appears unlikely that mixtures of these compounds will be separated on columns of porous glass, unless means of deactivating the active sites can be found.

According to Hillebrand, et al. (39), SbC15 boils at 140 °C and slowly dissociates into C12 and SbC13, thus explaining the appearance of two major peaks in the chromatogram of SbC15. The first peak is attribued to C12 and the second to SbC13. The first component gives a bright white light in the flame of the flame photometer burner, indicative of C12, and the second component gives a pale blue- white light which is indicative of SbC13.

Samples of NbC15 and NbOC13 failed to be eluted from the column. The tendency for oxygen- containing compounds to become A SbC15 Column Crushed unfused Vycor code 7930 B SnC14 16 feet long, 6 mm o. d. Input pressure 30 psi C GeC14 Flow rate 70 mi /min 2. 0 - Oven temperature 180 °C Flash 250 °C A vaporizer

0. 5 -

1 2 3 4 5 6 7 8 9 Time (minutes) Figure 14. Chromatograms of SnC14, GeC14 and SbC15 on porous glass. 53

"lost" on chromatographic columns has been reported by both Rogers

and Spitzer (71) and MacDonell, Noonan and Williams (56). It is not

surprising to find that NbO G1.3 is not eluted from the column. It is

not clear why NbC15 did not come off the column, but a possible ex- planation is that NbC15 is reduced by methanol groups, or other substances, in the porous glass. Porous glass appears to have some very interesting properties. Its usefulness for the separation of metal chlorides appears to be limited.

The Investigation of NaC1 and LiCl -KC1 Eutectic as the Column Material for the Gas Chromatography of Metal Chlorides

Introduction. Metal chloride melts have found widespread application in gas chromatography as the stationary phase in partition columns. The success of these columns in separating volatile metal chlorides have been limited so far, but the inertness of alkali chlorides toward highly reactive substances and their thermal stability have caused them to be of continuing interest. In addition, solid alkali chlorides have been the subject of investigations for use in gas -solid chromatography where they have been used as active solids, and in gas -liquid chromatography where they have been used as the solid support. Solid sodium chloride has been used as a fil- tration agent in the removal of impurities from gas streams of metal 54 chlorides in metallurgical processes.

Niobium pentachloride reacts with NaC1 and KC1 as follows:

NbC15 + NaC1 NaNbC16

NbC15 + KC1 =Zit KNbC16

Many other compounds, such as AlC13, FeC13, TaC15, etc. , under- go similar reactions. Several of the compounds formed boil without

decomposition (62). Equations relating the vapor pressure with the

temperature have been found, for NaC1 and KC1, respectively(62): 5000 log p - - + 11. 80 (NaC1) T ( ) 4T log p + 8. 15 (KC1) mm - T 0 where p mm is the vapor pressure of NbC15 over solid NaNbC16 and KNbC16, expressed in millimeters of mercury. The latter equations are recognized as examples of the Antoine Equation, applicable to inorganic and organic compounds over wide ranges of temperatures. It should be noted, however, that the chemical equations given above set metal chlorides apart from other compounds because of the formation of reaction products which boil without decomposition. It is apparent that the chemistry of these compounds with NaC1 and KC1 at high temperatures is not simple.

An attempt was made to determine if the affinity of NbC15 for

NaC1 could be used as a means of separating NbC15 from other metal chlorides by using a column in which the packing material is chromosorb P coated with NaCl. 55

Gas -liquid chromatography, because of the more ideal distribution between the liquid and gas phases, usually gives more ideal chromatograms. Eutectic mixtures afford a means to carry out gas - liquid chromatography at temperatures below the melting points of the pure substances. The vapor pressure of NbC15 over any eutectic mixture used as a stationary phase will be determined by the most stable (least volatile) complex salt formed. In the case of the eutectic mixture of LiCl and KC1 (41. 5 percent KC1, 58. 5 percent LiCl, M. P. 352° C), it is not possible to calculate the vapor pressure because the equation necessary for the calculation is not available. Nevertheless, an attempt was made to obtain suitable chromatographic separations of NbC15 on a column of the eutectic salt as the stationary phase.

Experimental. The apparatus used in this work is identical to that used in the preceding section. ,

Two chromatographic columns have been prepared. The first is a NaC1 column prepared by grinding dried NaCl to a fine powder in a water -free atmosphere and mixing a known amount of the powder with a weighed amount of Chromosorb P to give a stationary phase of 17. 5 percent NaCl. The mixture is fired at 750°C in a muffle furnace to distribute the salt onto the solid support. The resultant packing material, which has an appearance similar to the uncoated 56

solid support, is size graded to 50 -60 mesh and used to fill a glass column 20 feet long and six millimeters outside diameter.

A second column has been prepared by coating Chromosorb W with a known amount of LiCl -KC1 eutectic which was dried and puri- fied by bubbling anhydrous HC1 through the melt at 370° C. The per- centage of eutectic on the solid support is ten percent. The column is four feet long, six millimeters in diameter.

Results and Discussion. Chromatograms of NbC15 on the column of NaC1 at 370°C, flow rate 88 milliliters per minute, have very short adjusted retention volumes. The air peak appears as a shoulder on the NbC15 peak. The results at 265 °C are identical.

The low retention times are attributed to the decrease in surface area that occurs when the salt plugs the pores of the solid support, and to the low adsorption of NbC15 on NaC1

Chromatograms of GeC14 and SnC14 at 110°C, flow rate 50 milliliters per minute, were obtained. The retention times of the two compounds are identical and very short.

At 370° C, flow rate 88 milliliters per minute, NbC15 and NbOC13 did not elute from the column that was packed with Chromo- sorb W coated with the LiCl -KC1 eutectic. When the column was inspected it was very apparent that the yellow color of NbC15 had travelled only eight inches down the column. Shorter columns (ten 57 inches long) gave the same results until the temperature had been raised to 480° C. When NbC15 was eluted, at 480° C, the retention time was 5. 2 minutes. There was considerable tailing and the light emitted in the flame photometer burner was purple -red, instead of the usual white, due to the presence of potassium and lithium atoms in the gas stream. After the solute had passed through the flame, the color returned to normal. Evidently, KNbC16 and LiNbC16 evaporate from the column at 480'C without decomposition and are carried from the column.

After many samples of NbC15 had passed through the column, ) the normally white packing material was observed to have turned a grey -black color. The dark color is believed to be a lower oxidation state of niobium. All chlorides of the lower oxidation states of niobium are black or dark brown.

Investigation of Fluoropak 80 as an Active Solid in the Gas Chromatography of Metal Chlorides

Introduction. Because of its chemical inertness, Teflon has found widespread applications as the solid support, but has attracted little attention as an active solid in gas chromatography probably because until Teflon-6 became available the surface area of ground Teflon was small in comparison with diatomaceous earth. Staszewski and Janak (76) found that Teflon showed remarkably little peak assymetry 58 for polar compounds having a tendency to form hydrogen bonds. In order to resolve mixtures of metal chlorides, it is necessary to reduce the tailing that frequently accompanies gas chromatography, particularly gas -solid chromatography. Accordingly, a study was undertaken to determine the possibility of separating polar, reactive compounds on Teflon.

Experimental. The apparatus used in this experiment is described in Section IV A, excepting insofar as the liquid sampling is concerned. Liquid samples are injected into the glass boat of the solid sampler by a Teflon -tipped hypodermic syringe equipped with a Teflon needle. Subsequently, the sample is pushed into the flash vaporizer as described previously.

A glass column 12 feet long and six millimeter outside diameter is filled with Fluoropak 80 by the method described on page 26. Be- cause the particles of Teflon are irregularly shaped, the packing density is not great.

Results and Discussion. Ethyl acetate chromatograms on the Teflon column at 137°C show small retention times, as expected. The width of the peak is attributed to the inlet being too large, con- sequently the sample does not enter the column as solute plug.

Stannic chloride, in comparison, gives a broader peak still. However, 59

these samples are quite small, and with a better sampling system,

better chromatograms may be realized. Chromatograms of ethyl

acetate and SnC14 are shown in Figure 15.

Chromatograms of SbC15 are shown in Figure 16, In Figure

14, a chromatogram of SbC15 on porous glass gave two peaks, attri-

buted to the decomposition of SbC15 into C12 and SbC13. In Figure 16

all three curves shown have two major peaks, substantiating the results indicated previously.

Figure 17 shows individual chromatograms of NbC15 and

NbOC13. The separation of the two compounds is not as complete as

might be expected, caused mainly by the chemical nature of the com-

pounds, namely, the tendency of the compounds to form dimers, or

inter -molecular compounds, such as NbC15 - NbOC13. Because of

this tendency, it is quite difficult to achieve complete separation

since some of one compound is carried along with the other, and vice versa, in the chromatographic process.

The formation of dimers, with oxygen bridges, also contributes to the spreading of the NbOC13 peak. In fact, studies of NbOC13 have indicated that it exists in the solid phase as a polymer with Nb -O -Nb bridges (27). Oven temperature 137° C 1. 0- Flash vaporizer 2703C Detector temperature 160° C Flow rate 25 mis /min Input pressure 6 psi

Sample size about 1 µl Column material Fluoropak 80

Ethyl acetate

1 2 3 4 5 Time (minutes)

Figure 15. Chromatograms of ethyl acetate and SnC14 on Fluoropak 80 Figure

Detector response (mv) 0,5- 1 1. 16. 01 5- 0 C B A Chromatograms SbC15 SbC15 SbC15 at at at 2 230°C, 192°C, 137°C, of flowrate flowrate flowrate SbC15 3 4 on 35 35 50 Fluoropak ml/min ml/min ml/min Time (minutes) 6 80. Column Filament Input Detector Flash Oven pressure temperature vaporizer material temperature current 8 _10 Fluoropak 100 240°C 250° various 10 psi ma C 80 12 NbC15 Oven temperature 220° C Flash vaporizer 330°C HC1 Detector 2. 0 - temperature 226°C Flow rate 50 mis /min Input pressure 10 psi Filament current 100 ma i Column material Fluropak 80

0. 5 -

0 1 2 3 4 Time (minutes) Figure 17. Chromatograms of NbC15 and NbOC13 on. Fluoropak 80 63

The Investigation of FX -45 as a Partition Agent for the Gas Chromatography of Metal Chlorides.

Introduction. The limited success of solid Teflon in separating

corrosive metal chlorides points the way to further chromatographic investigation of polytetrafluoroethylene. Gas -liquid chromatography results in a larger number of theoretical plates per unit length of column than gas -solid chromatography because more of the solute

can dissolve in the liquid than can be absorbed on the surface. Al-

though polychlorotrifluoroethylene has been used successfully in

separating corrosive fluorine compounds (24), no report of the use

of liquid polytetrafluoroethylene has been published ( 5 ).

A new fluorocarbon polymer, FX -45 (Minnesota Mining and

Manufacturing Company, St. P a ul , Minn. ) is a liquid at room

temperature and has a reported vapor pressure at 250 °C of five to

ten, expressed in millimeters of mercury. A column of FX -45 on

acid -washed Chromosorb W was prepared and used for the chromatographic analysis of metal chlorides.

Experimental. A general description of the apparatus used in

this experiment is given on pages 11 -33. For this work, and subsequent gas liquid chromatography, instead of the solid sampling system, the liquid sampling system shown in Figure 3 is used.

To prepare the packing material, a weighed amount of FX -45 64

is dissolved in a special fluorocarbon solvent, FX -78. Conventional

solvents do not dissolve FX -45 readily. The solution is placed in a

12 centimeter Petri dish and a weighed quantity of 50 -60 mesh acid -

washed Chromosorb W is added. The slurry is stirred gently for five minutes and then occasionally until the solvent has evaporated.

When the coated Chromosorb W appears dry, the Petri dish is

placed in an oven at 110 °C to expel the last traces of the solvent.

Then the material is size -graded to 50 -60 mesh and used to fill the

glass column, as described on page 26. The total length of the column is 24.5 feet. Finally the assembled columns and detector,

shown in Figure 5, are placed in the heating oven. The chromato-

graph is heated to 100 °C and preconditioned by passing helium through the column at a slow flow rate (one to five milliliters per minute) for about eight hours.

Results and Discussion. Chromatograms of AsC13, SnC14 and

CC14 were obtained at temperatures ranging from 52 °C to 120 °C.

At low temperatures AsC13 and SnC14 do not give symmetrical peaks for samples greater than 0. 5 µl. Figure 18 shows chromatograms

of AsC13 and SnC14, at 68 °C, injected by the CC14 displacement technique. Retention times for the two compounds are identical, pointing out the impossibility of separating these two compounds by gas chromatography with FX -45 as the liquid phase. FX -45 is 2. 5 Oven 2. 5- temperature 68° C Detector temperature 68° C 1 Flash vaporizer 225 °C 2. 0- Flow rate 88 mis/min Input pressure 2. 0 Filament current 100 ma Column FX -45 E Sample size 1 µl 1. 5- 1. 5 ao co a) 5-i

(1) rd 1. 0 1. o 0 U CL) P4

0. 5 0. 5

o- 5 6 7 8 9 10 11 5 6 7 8 9 10 11 Time (minutes) Figure 18. SnC14 and AsC13 on FX -45. 66

thermally stable up to 145°C, where the base line of the chromatograms begins to be quite noisy, indicating excessive vaporization of the liquid. No decomposition of the FX -45 is observed at tempera-

tures up to 200°C. Even though the resolution of AsC13 and SnC14 was not accomplished, the increase of the adjusted retention volume over comparable gas -solid columns indicate that FX -45 may well be adaptable to analysis of other materials, especially in view of the improved symmetry of the peaks.

The Investigation of Halocarbon 6 -00 as a Partition Agent for the Gas Chromotography of Metal Chlorides.

Introduction. The failure of AsC13 and SnC14 to be resolved on a fluorocarbon containing no chlorine, FX -45, indicates that these two metal chlorides are not sufficiently soluble in the liquid phase, i. e. , the distribution constant is small. Polychlorotrifluoroethylene has found applications in the separation of fluorine containing corn- pounds, and has been stable toward many corrosive compounds, such as C12, C1F, HF, etc. The possibility of enhanced solubility of metal chlorides led to an investigation of a polychlorotrifluoroethylene, Halocarbon 6 -00 ( Halocarbon Products, Incorporated, Hackensack, N. J.) as a liquid phase for the separation of metal chlorides.

Experimental. The apparatus used in this experiment is 67

identical to that used in Section IV F. .

Partition columns are filled by the method described on page 26. The packing material consisting of 24.5 percent Halocar-

bon 6 -00 on acid washed Chromosorb W, size graded to 50 -60 mesh,

is prepared by the method described in Section IV F. - Carbon tetrachloride is used as the solvent.

Results and Discussion. Chromatograms obtained using the apparatus described exhibited little of the severe tailing and other

anomalous effects that have plagued othe r workers in the field of gas

chromatography of metal chlorides. A typical chromatogram is

shown in Figure 19. The first peak appearing is GeC14 which has a retention time at the temperature of the chromatogram only one percent greater than carbon tetrachloride. Thus the flushing technique described on page 21 could not be used. Rather, the sample is injected by the simple displacement of the sample into the chromatograph by a column of air as the plunger is pushed in. All three components are nearly symmetrical and well resolved. Furthermore, the retention times of the various components, reduced to zero sample size, are reproducible to within the accuracy of the experimental measurement of time, i. e. , about one second, or 0. 5 percent.

Figure 20 shows the separation of CC14, SnC14, AsC13 and

TiC14. Only AsC13 and TiC14 are not well resolved. It may be 68 1. 5

GeC14

1. 0'_ SnC1 4

AsC13

2 3 4 5 6 7 8 9 10 11 Time (Minutes)

Figure 19. Chromatographic Separation of GeCÌ, SnC14 and AsC13 Figure

Peak Response (MV) 20. 0. 1.0 1. o 5 5 0 AsC13 Gas Chromatographic 1 and J 2 TiC14. A 3 Time S 4 (Minutes) Separation 5 6 D C B A of TiC14 AsC13 SnC14 CC14 7 CC14, 8 SnC14, 9 10 69 70 observed that all components shown in Figures 19 and 20 elute in the order of their boiling points, as would be expected when the distribution between the stationary and mobile phases is normal. Calculations of HETP were made by the method of Keulemans over the range of 92°C to 126°C. A consistant decrease in HETP occurs as the temperature increases and the peaks become sharper.

This effect is particularly noticeable for AsC13 and TiC14 which tend to broaden at temperatures much below 120°C. As given in

Table I for AsC13 the change in HETP is from 0. 83 cm at 92°C to

0. 46 cm at 126°C. For SnC14 the change is only 1. 06 cm to 0. 65 cm, indicating the higher volatility of SnC14 at 92° C. In addition, the tailing decreases as the temperature is increased, However, the ratios of retention times decrease, as the distance between peaks decreases, so that the resolution of AsC13 and SnC14 actually decreases above 120°C. For example, at 174°C the ratio is 1. 09, and the peaks are no longer satisfactorily resolved. Increasing the temperature also decreases the effect of sample size on the retention times up to about 120°C for AsC13 and SnC14, and generally improves the symmetry of the peaks. Below 120°C larger samples (greater than 4 mg) of AsC13 and TiC14 give peaks that are slightly skewed.

At 81°C the effect of sample size on the retention time is 0. 39 minutes per milligram for AsC13 but has decreased to only 0. 13 minutes per milligram at 120°C as the vapor pressure of the 71 compound increases.

Table I. HETP Values of CC14,- AsC13 and SnC14 at Various Temperatures.

HETP (cm) T(° C) CC14 AsC13 SnC14

92 - 0. 83 1. 06

100 0. 83 0. 69 0. 82

110 0.68 0.51 0.66

126 0. 49 O. 42 0. 65

Solutions of SbC13 in CC14 and AsC13, when injected into the chromatograph, give no peak other than those of the solvent. Even at 185 ®C no SbC13 peak is obtained. The only evidence of the presence of SbC13 is the severe tailing of the AsC13 peak which is signifi- cantly greater than it is for a pure sample of the AsC13. This effect may be caused by the formation of a SbC13 -AsC13 dimer which is eluted from the column, or decomposes as it passes down the column, releasing AsC13 which is subsequently eluted normally.

Because analysis of mixtures of metal chlorides by gas chromatography offers definite advantages over many other conventional methods, an attempt was made to render the chromatographic separation of AsC13 and SnC14 quantitative. The conditions of the calibration and analysis are as follows: Corrected flow rate 88 72 millimeters per minute, oven temperature 109°C, flash vaporizer temperature 225°C, detector filament current 100 ma. The peak areas, obtained by electrical integration, are plotted against the sample size. Straight lines are obtained, as shown in Figure 21. Table II gives precision data for the calibration. Most of the error in the calibration is caused by the sampling. While the precision shown is considered quite good, a great deal of experimental technique is required for such reproducibility.

Solutions of AsC13 and SnC14 are prepared by mixing measured quantities of pure compounds together in an inert atmosphere. A precision syringe is used to measure the volume of the two liquids. A typical chromatogram of the resolution of the mixtures is shown in

Figure 19. The results of the integration are given in Table III. The accuracy and precision of the analysis offer considerable promise for the analysis of metal chlorides by gas chromatography.

By comparing the chromatograms of the mixtures with those of pure compounds, it was found that about 0. 1 milligrams of SnC14 emerged with the AsC13 peak as a contamination, and the amount of contamination is almost independent of sample size. Thus, larger samples, up to 15 milligrams, give greater accuracy. No attempt was made to correct the calibration curve for the inaccuracy caused by this contamination, because the contamination error is still less than the sampling error. AsC13

16_ SnC1

"a12-

8- x co

6 8 10 12 14 Integral of peak area (volts) Figure 21. Calibration plot of AsC13 and SnC14 on Halocarbon 6 -00. 74

Table II. Calibration of Peak Areas for AsC13 and SnC14

SnC14

Sample size (µl) 1.0 2.0 3.0 4.0 5.0 Weight of Sample (mg) 2. 23 4. 46 6. 69 8. 92 11. 13 Integral of 1. 98 4. 48 6. 45 8. 62 10. 40 Peak Area 2. 15 4. 33 6. 20 8. 54 10. 62 (volts) 2.07 4.36 6.50 8.85 10.58 2.00 4:40 6 50 Mean 2.05 4.40 6.41 8.67 10.53 Standard Deviation 0. 07 0. 06 0. 12 0. 13 0. 10 Slope = 2. 14 volts /µl

AsC13

Weight of Sample (mg) 2. 16 4. 32 6. 48 8. 64 10. 80 Integral of 2. 41 4. 60 7. 00 9. 63 12. 30 Peak Area 2. 64 4. 78 7. 47 9. 77 12. 39 (volts) 2.31 4.80 7.14 9.60 12. 18 2.19 4.86 7.32 9.59 12.13 Mean 2.39 4.76 7.23 9.65 12.24 Standard Deviation 0.16 0.08 0.18 .07 - 0. 10 Slope = 2. 41 volts /µl 75

Table III. Analysis of SnC14 /AsC13 Mixtures

SnC14 AsC13 m g F(mg) Error Kfmg Found Error Sample 1 1. 11 0.96 -0. 15 9.73 9.50 --0.23 1.16 +0.05 9.60 -0. 13 1.16 +0.05 9.88 +0.15 1.02 -0.09 9.49 -0.24 1.11 0.00 9.30 -0.43 1.00 -0.11 9.60 -0.23 Mean 1.07 -0.04 9.56 -0.22 Standard Deviation 0. 09 0. 19

Sample 2 5. 48 -0. 07 5. 60 +0. 19 5.40 -0.15 5.43 +0.02 5.55 5.48 -0.07 5.41 5.53 +0.12 5.54 -0.01 5.51 +0.10 5.20 -0.35 5.63 +0.19

Mean 5.42 -0. 13 5.54 +0.12 Standard Deviation 0. 13 0. 08

______MO =Ill IMP GO IN Sample 3 10. 00 9. 81 -0. 19 0. 99 -0. 09 9. 91 -0. 09 1. 08 1. 12 +0. 04 9. 96 -0. 04 0. 99 -0. 09 9. 90 -0. 10 0. 99 -0. 09 Mean 9.90 -0.11 1.02 -0.06 Standard Deviation 0. 06 0. 06 76

The log retention volume has been plotted against the reciprocal of the absolute temperature, as shown in Figure 22. The plots gave straight lines for all compounds, although there is an evident deviation for AsC13 and SnC14 at higher temperatures, indicating a tern - perature dependency of the heats of solution. Carbon tetrachloride shows a slight change in slope about 600C, the melting point of the liquid phase. Molar heats of solution calculated by least squares analysis of the data, are given in Table IV. Molar heats of vaporization were obtained from the Handbook of Chemistry and Physics (9).

Table IV. Heats of Solution and Vaporization of Metal Chlorides Molar Heat of Molar Heat of Compound Solution (Kcal /mole) Vaporization (Kcal /mole)

CC14 6. 3 (60°C< ) 7. 0

GeC14 5. 6 7. 0

SnC14 7. 8 7. 9

AsC13 8. 9 7. 6

TiC14 8. 7 8. 3 77

100 TiC14 AsC13

SnC14 60 CC1

20 bo

4 2.4 2.6 2,8 3.0 3.2 1/T x 103 Figure 22, Log V as a function of 1/T for inorganic chlorides. 78

Investigation of the Gas Chromatography of Metal Bromides on Halocarbon 6 -00.

In the analysis of mixtures of AsC13, SnC14 and SbC13, the compounds are usually separated by their selective distillation as chlorides. Arsenic trichloride is distilled at 95°C (64) or 110° C

( .3 ), SbC13 at 155°C in the presence of H3PO4 to prevent the distillation of SnC14, and SnC14 at 140°C upon the of a HC1 /HBr 4 addition solution. It is interesting to note that when HBr is added to a solution containing tin at 140°C, tin distills apparently as the tetrabromide

(39).(39 Since SnBr4 has a higher boiling point than SnC14, this effect is surprising, indeed.

Gas chromatography affords a method not available heretofore for investigating the nature of the distillation of tin chlorides and bromides in the absence of water vapors. A column of Halocarbon

6 -00 on Chromosorb W has proven thermally stable to 185°C and can be used for the gas chromatography of stannic tetrabromide, and other metal halides having vapor pressures that are sufficiently high.

Experimental. The apparatus for this investigation is identical to that used in the preceding section.

The arsenous and stannic bromide reagents used in this investigation were obtained from City Chemical Company, New York,

N. Y. They were used without additional purification. 79

Results and Discussion. Chromatograms of AsC13 and SnC14 at temperatures up to 185 °C show no anomalous behavior, as shown in Figures 23 and 24. The corresponding bromide chromatograms do not give symmetrical peaks as shown in Figures 23 and 24. It is possible that there are impurities in the reagent causing the asym- metric peaks, but more likely the preceding shoulder is a reaction product between the reagent and some component in the column. Be- havior such as this has been experienced by Keller (46) in his work with stannic and titanium chlorides and hydrocarbon liquid phases.

When a mixture of SnC14 and SnBr4 are injected into the chromatograph a totally unexpected result is obtained as shown in Figure 23. The SnC14 and SnBr4 peaks are drastically altered and the recorder trace never returns to zero as it does when either pure SnC14 or SnBr4 is injected into the chromatograph.

Figure 24 shows that AsC13 and AsBr3 give very similar results. Apparently the phenomenon being observed does not depend on the nature of the metal involved. The inability of the recorder trace to return to zero until the second major peak passes indicates that the change in the SnC14 and SnBr4 peaks, or corresponding in the AsC13 and AsBr3 peaks, is not due to a chemical reaction with the column material but to a reaction between the solutes themselves. It is suggested therefore, that the following chemical exchanges take place, either in the liquid or gas phases Figure Recorder resp 1. 5 23. 0 -A C B SnC14 SnBr4 SnC14 Chromatograms + SnBr4 2 of SnC14 3 and Time SnBr4 4 (minutes) on Halocarbon 5 6 6 -00. 7 8 9 10 Figure

Recorder response 0. 1. 1. 0 5 0 5 24. C B A Chromatograms AsC13 AsBr3 AsC13 + AsBr3 2 of AsC13 3 and Time AsBr3 4 (minutes) Column Filament Sample Input Flow Detector Flame Oven temperature on pressure rate temperature Halocarbon 5 vaporizer size temperature current 8 6 -00. B 24. 4 100 20 84 185° 300° 185 7 µl psi mis 5% 'C ma C C Halocarbon /min 8 9 6 -00 ro 82

SnC14 + SnBr4 SnC13Br + SnBr3C1

SnC14 + SnBr4 2 SnC12Br2 and so forth. Similar reactions in the case of arsénic would give corresponding exchanges:

AsC13 + AsBr3 r AsC1Br2 + AsBr2Cl

Further reaction between the reaction products and the starting compounds may also take place. Thus, compounds having intermediate volatilities would be eluted from the chromatograph in between the pure chlorides and bromides, preventing the return of the recorder trace to zero. 83

CONCLUSIONS

Grant (33) reported that the flame emission detector (flame photometer) had a sensitivity about ten times greater than an equivalent thermal conductivity detector. The flame photometer detector developed in the course of this work is also more sensitive than many .thermal conductivity detectors, for compounds having a strong flame emission, but the noise level is higher. In cases where there is no thermal drift in the thermal conductivity detector, it is doubt- ful that an increase in sensitivity, with the increase in the noise level, is to the advantage of the flame photometer detector.

The advantages accruing to the user of a flame photometer detector, such as the one described in this work, are the following:

1. A flame photometer detector may be operated in such a way that the solute does not come into contact with the sensing element. Therefore, there is no difficulty in the detection of corrosive substances that have a strong flame emission.

2. The detector is completely insensitive to variations in the flow rate of the carrier gas.

3. The flame photometer is not only almost completely insensitive to changes in the temperature of the burner, but the detector may be operated at temperatures higher than most other detectors. The upper limit is determined by the materials used to construct the burner, and ultimately to the effect the temperature has on the combustion of the fuel. The detector used in this work is capable of being operated up to 700 ®C, below the melting point of silver solder. 84

4. A flame photometer detector is selective in that it is totally insensitive to some substances (such as HC1, H2O, etc.) and with the use of filters or a monochromator can be made more selective still. Monkman and Dubois (61) used this selectivity to detect halogenated hydrocarbons in the presence of other components, a feat impossible with most other detectors.

On the other hand, the sensitivity of the detector is dependent on the position of the photomultiplier tube housing with respect to the burner, and the housing must be firmly anchored to the outer casing of the oven to prevent any mechanical movement. The most serious limitation, however, is the dependency of the sensitivity on the flow of fuel and air to the burner. Because of the day -to -day change in the sensitivity, quantitative results are very difficult, unless in- ternal standards are developed.

Most of the data presented in this thesis was obtained in experiments where the thermal conductivity detector was used. Of the two detectors, the thermal conductivity detector gave the most satisfactory results because the noise level was exceptionally low, all components in the gas stream were detectable and there was no change in the sensitivity from day -to -day for a given detector temperature and filament current. The performance of the thermal conductivity detector is considered most satisfactory in view of the corrosive nature of the solutes.

Some of the most interesting chromatograms in this work came from experiments where uncoated porous glass was used as the 85 packing material in the preparation of columns. If porous glass can be treated in such a way that the active sites remain deactivated at high temperatures (up to 500°C) it may be possible to separate components with very high boiling points, not heretofore separable by gas chromatography.

The success in separating metal halides on columns of solid alkali halides in this work was very limited, and it appears unlikely that future developments will lead to greater success. Inorganic salt eutectics offer some promise but it now appears that much work needs to be done before one can be truly optimistic in regard to the use of these melts as liquid phases in gas chromatography.

Arsenous trichloride and stannic tetrachloride were not separated on a column where polytetrafluoroethylene (FX -45) was used as the liquid phase. However, the greater temperature stability of tetrafluoroethylene polymers, in comparison with polychlorotrifluoroethylene (Kel -F, Halocarbon), may well lead to the use of liquid PTFE for high temperature gas- liquid chromatography.

The use of Teflon as a solid support in the analysis of inorganic compounds has already been widely reported. In view of recent ad- vances in making Teflon with much higher surface areas, the applications will probably increase.

Work where Halocarbon 6 -00 was used has shown conclusively that this material is suitable for the analysis of many metal chlorides 86 and may be extended to many other compounds. At present the limitation imposed by inadequate sampling systems, especially for very

small samples, restrict the applications of Halocarbon 6 -00 in the analysis of metal halides more than any other factor.

The success of Halocarbon 6 -00 in the analysis of metal halides may best be evaluated by comparing chromatograms obtained in the

course of this work and those published previously with regard to the

symmetry and the quantitative reproducibility of the peaks. 87

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