A Review of EPA Sample Preparation Techniques for Organic Compound

1120 LCGC VOLUME 19 NUMBER 11 NOVEMBER 2001 www.chromatographyonline.com

A Review of EPA Sample Preparation Techniques for SampleSample PrepPrep Organic Compound Analysis Perspectives of Liquid and Solid Samples

nvironmental analysis often involves methods), high performance liquid chro- analytes in a wide variety of matrices, matography (HPLC) (8300 series meth- ranging from air to sewage water to ods), and GC–Fourier transform infrared Guest Author E Greg LeBlanc polluted soil samples. Proper sample prepa- (8400 series methods). Organic analysts are ration procedures are necessary to achieve concerned with more than 450 analytes. optimum analytical results. The U.S. Envi- Compared with inorganic analytical lab- ronmental Protection Agency (EPA) is the oratories, organic laboratories face a major government body responsible for the defini- challenge to cost-effectively prepare and tion, development, and enforcement of analyze the wide variety of analytes from Collecting, preserving, analytical measurements for specific pollu- environmental samples. As with any and preparing samples tants that are deemed to be harmful to the process, the primary focus is on the deter- environment. The EPA’s Test Methods for minative step that produces the result. are critical to producing Evaluating Solid Waste — SW-846 — pro- However, the front-end work of sampling, accurate and reliable vides a comprehensive source of informa- preservation, and sample preparation is crit- results in the analysis of tion about sampling, sample preparation, ical to producing accurate and reliable organic compounds. This analysis, and reporting for compliance with results. In this report, I will review the sam- the Resource Conservation and Recovery ple preparation techniques — 3500 and “Sample Prep Act. Furthermore, SW-846 outlines test 3600 series methods — that are available to Perspectives” column procedures used to characterize solid waste organic laboratories under SW-846 for the reviews sample in accordance with 40 Code of Federal Reg- analysis of non- and semivolatile com- ulations (CFR) Part 261, Identification and pounds from environmental samples. The preparation techniques Listing of Hazardous Waste. The sample 3500 series methods cover the extraction that are available to preparation and analytical procedures or steps, and the 3600 series methods include organic laboratories determinative steps are categorized by the the cleanup steps. under SW-846 regulations analyte, either inorganic or organic. Inorganic analyte procedures are charac- Extraction Techniques for the analysis of non- terized by acid digestion steps using con- The sample matrix and analytes define and semivolatile ventional or microwave heating (3000 the 3500 series sample extraction methods. compounds from series methods), followed by atomic absorp- The matrix is aqueous, solid, an air sam- tion or emission spectroscopy (6000 and pling train, or nonaqueous soluble. The environmental samples. 7000 series methods). Inorganic analysts are analytes are characterized as either non- or concerned with approximately 30 analytes semivolatile organic compounds. All sam- or elements for environmental analysis. ples analyzed for nonvolatile or semivolatile Organic analyte procedures are char- organic compounds require a solvent acterized by solvent extraction steps for extraction step, with the exception of nonvolatile and semivolatile analytes (3500 nonaqueous solvent–soluble samples. The series methods) and postextraction cleanup solvent-soluble samples use a simple solvent (3600 series methods). Sample preparation dilution step, a so-called dilute-and-shoot methods for volatile compounds define method. Because both solid and liquid methodologies such as purge-and-trap, dis- samples are injected as an extracted liquid, Ronald E. Majors tillation, headspace, or dilution in the 5000 I first will discuss sample preparation tech- Sample Prep Perspectives Editor series methods. The analytical steps are gas niques for solid samples and later those for chromatography (GC) (8000–8200 series aqueous samples. www.chromatographyonline.com NOVEMBER 2001 LCGC VOLUME 19 NUMBER 11 1123 Solid samples: The technologies used method used to enhance the action of the ume to 1–2 mL. This three-stage approach for the extraction of non- and semivolatile solvent for the extraction. They range from shortens the extraction step to 2 h, because organic compounds from solid samples are classic Soxhlet extraction to modern micro- it provides direct contact between the sam- more diverse than for water and other liq- wave extraction. For this discussion, I will ple and solvent at the solvent’s boiling uid samples. The techniques vary by the define a solid sample as clay, soil, sludge, point. It also reduces the consumption of sediment, or waste. solvent. For more details about automated Soxhlet extraction (EPA Method 3540C): Soxhlet extraction, please see Arment’s Analytical chemists have used Soxhlet review (1). extraction for more than 100 years (1). Pressurized-fluid extraction (EPA Method (a) (b) (c) This method is the classic approach to 3545A): Pressurized-fluid extraction is one extracting solid samples for a spectrum of of the latest technologies to be approved for non- and semivolatile organic compounds. solid-sample extraction. The method per- It works in a manner analogous to continu- forms extractions at elevated solvent tem- ous liquid–liquid extraction, except the peratures and pressures to achieve perfor- sample is solid instead of liquid. The sam- mance comparable to the Soxhlet technique ple, held in a porous cellulose thimble, is with a significant reduction in time and sol- extracted continuously with a fresh aliquot vent consumption. The instrumentation to of distilled and condensed solvent. Thus, perform pressurized-fluid extraction, more the extraction is performed at temperatures commonly known by its trade name of below the solvent’s boiling point. In prac- accelerated solvent extraction, is semiauto- tice, the method is simple to perform. The mated (see Figure 2). After loading a sam- technique is time consuming but can be ple into the extraction cell and sealing it, automated, and it has a low acquisition the instrument performs the extraction, cost. Typically, the extraction step requires separation, and collection steps automati- 16–24 h at 4–6 cycles/h. cally. Samples are processed sequentially in Automated Soxhlet extraction (EPA batches of as many as 24 samples. Equip- Figure 1: Three-step extraction procedure Method 3541): This technique is an auto- ment is available that will perform the using the Foss-Tecator Soxtec Avanti automated version of the classic Soxhlet extraction of six samples simultaneously mated extraction system. Shown are (a) the sol- approach to extracting solid samples, with (2). ubilization of extractable matter from sample immersed in boiling solvent, (b) rinsing of two modifications (Figure 1). This The principle of pressurized-fluid extrac- extracted solvent (similar to conventional Soxh- approach initially immerses the thimble tion is simple. The sample (or a sample let extraction), and (c) concentration of the that contains the sample directly into the mixed with a drying agent) is loaded into a extracted sample by evaporation and collection boiling solvent. Then, the thimble is high-pressure, high-temperature extraction of distilled solvent for reuse or disposal. During moved above the solvent to mimic the cell, which is sealed. The cell is heated to evaporation, solvent is blocked from returning to the extraction cup and flows into a collec- rinse-extraction step of Soxhlet extraction. the extraction temperature, which often is tion tank. (Courtesy of Foss North America, Finally, a concentration step using modern two- to threefold the atmospheric boiling Eden Prairie, Minnesota.) automated equipment reduces the final vol- point of the solvent; the extracting solvent is added and held in contact with the sample for 5–10 min; the extract then is flushed from the cell into the collection vessel with a volume equal to 60–75% of Load sample the cell volume; and finally the extract is into cell purged with nitrogen. In pressurized-fluid extraction, the sample is diluted by the vol- Fill cell ume of extraction solvent and must be con- with solvent Pump centrated before analysis. For more details about the pressurized-fluid extraction tech- Heat and pressurize cell nique, please see the review by Richter (3). Microwave extraction (EPA Method Hold sample at pres- 3546): Microwave extraction is the latest sure and temperature technique to be included in SW-846. The Solvent microwave extraction method is the process Pump clean solvent Oven into sample cell Extraction of heating solid sample-solvent mixtures in cell a sealed (closed) vessel with microwave Purge solvent from Nitrogen Vent energy under temperature-controlled condi- cell with nitrogen gas tions. Although used less frequently, the Collection vial extraction also can be performed in an Extract ready open vessel at atmospheric pressure. Figure for analysis 3 depicts a typical microwave extraction cell used in a closed extraction system. This sys- Figure 2: Schematic diagram of a pressurized-fluid extraction system. (Courtesy of Dionex Corp., tem provides significant temperature eleva- Sunnyvale, California.) tion above the atmospheric boiling point of 1124 LCGC VOLUME 19 NUMBER 11 NOVEMBER 2001 www.chromatographyonline.com the solvent, accelerates the extraction Supercritical fluid extraction (EPA Meth- modifier exits the system, and the target process, and yields performance compara- ods 3560, 3561, and 3562): These three compounds are collected in a vessel that ble to the standard Soxhlet method. Sam- methods use supercritical carbon dioxide contains a suitable solvent or sorbent mate- ples are processed in batches of as many as or carbon dioxide with a modifier to rial. For more information about SFE, 14 samples per run. The microwave energy extract total recoverable hydrocarbons, consult reference 5. provides very rapid heating of the sample polycyclic aromatic hydrocarbons (PAHs), Comparison of solid sample extraction batch to the elevated temperatures, which polychlorinated biphenyls (PCBs), and techniques: Table I compares the EPA sam- shortens the extraction time to 10–20 min organochlorine pesticides. Supercritical car- ple preparation methods for solid samples. per batch. Solvent consumption is only bon dioxide or carbon dioxide–organic It compares the above techniques with 25–50 mL per sample. After the heating modifier extracts the sample, which is held regard to solvent use, extraction time, cycle is complete, the samples are cooled in an extraction vessel within a closed sys- acquisition costs, and operating costs. and the sample is filtered to separate the tem. Supercritical fluids such as carbon Clearly, the modern techniques provide sample from the extract for the analytical dioxide have properties of both liquids and more rapid extraction with a minimal step. The technique was reviewed in gases, which make them desirable for amount of organic solvent required. How- LCGC (4). extraction. When its temperature and pres- ever, some of them are expensive compared Ultrasonic extraction (EPA Method sure are controlled, carbon dioxide has the with the classic methods. 3550C): This method uses mechanical penetrating characteristics of gases and the Aqueous samples: Several solvent energy in the form of a shearing action, solvating properties of liquids. An organic extraction techniques for the analysis of which is produced by a low-frequency modifier such as methanol, acetonitrile, non- and semivolatile organic compounds sound wave. The sample is immersed in an or isopropanol can be used to assist the in a liquid state are available under SW- ultrasonic bath with solvent and subjected extraction of polar analytes. The primary 846. Separatory funnel liquid–liquid to ultrasonic radiation for 2–3 min. The operating parameters are the carbon diox- extraction, continuous liquid–liquid sample is separated from the extract by ide or carbon dioxide–modifier flow rates, extraction, and solid-phase extraction vacuum filtration or centrifugation. The temperature, pressure, and dynamic or sta- (SPE) techniques most often are used for process is repeated 2–3 times, and the tic mode of extraction. liquid matrices. The solvents used for extracts are combined for the analytical Figure 4 shows a schematic of a typical liquid–liquid extraction techniques are step. This technique has the benefit of supercritical fluid extraction (SFE) system. insoluble in the aqueous sample. The tech- shortened extraction times, but it sacrifices In the static mode, the extraction cell fills niques are applicable for the extraction of performance relative to the Soxhlet tech- the extraction vessel with the supercritical water-insoluble and slightly water-soluble nique. The solvent receives only minor fluid and holds it in the vessel for a speci- organic compounds. heating of a few degrees above room tem- fied period of time. In the dynamic mode, Separatory funnel liquid–liquid extraction perature and, thus, cannot provide as thor- the supercritical fluid passes through the (EPA Method 3510C): This technique is a ough extraction of difficult matrices such extraction vessel continuously. The depres- classic approach to extraction for liquid as aged soil samples. surized carbon dioxide or carbon dioxide– samples for a spectrum of non- and semi-

Temperature probe Cryogenic zone 4

Cryogenic zone 3

Restrictor Seal Chamber cover Cryogenic with zone 2 sample Impinged surface or region Cryogenic zone 1 Liner Preheat Microwave energy Carbon dioxide pump Sample and solvent Liquid carbon dioxide Vessel support module Extraction Expansion Collection Figure 3: Sample and solvent in a Reconstitution GreenChem extraction vessel. Contents are rapidly heated to elevated temperatures and pressures using microwave energy. (Courtesy of CEM Corp., Matthews, North Carolina.) Figure 4: Schematic diagram of a generic SFE system showing four cryogenic zones. (Courtesy of Agilent Technologies, Wilmington, Delaware.) www.chromatographyonline.com NOVEMBER 2001 LCGC VOLUME 19 NUMBER 11 1125

Table I: Comparison of 3500 series extraction techniques for solid samples*

Average Solvent Use Average Extraction Operating Cost EPA Method Number Extraction Technique (mL/sample) Time (min/sample) Acquisition Cost per Sample 3540B Soxhlet 300 960–1440 Very low Very high 3541 Automated Soxhlet 50 120 Moderate Low to moderate 3545A Pressurized-ﬂuid extraction 10–30 10–15 High Low 3546 Microwave-accelerated extraction 25–40 10–20 Moderate Low 3550C Ultrasonic nebulization 300 30 Low High 3560, 3561, and 3562† SFE 10 20–50 Moderate to high Moderate to high

* Examples of solid samples include soils, sediments, fly ashes, sludges, and solid wastes that are amenable to extraction with conventional solvents. † SFE is limited to the analysis of total recoverable hydrocarbons, PAHs, organochlorine pesticides, and PCBs. volatile organic compounds. An aqueous semivolatile organic compounds. Figure 5 Solid-phase extraction (EPA Method sample is mixed in a separatory funnel illustrates the construction principles of 3535C): This extraction technique for with an immiscible organic solvent that is two types of continuous liquid–liquid aqueous samples is the latest to be added denser than water. After standing, the mix- extraction systems. The solvent is added to to the SW-846 manual, and it involves the ture will separate into two phases with the the top of a liquid–liquid extractor, which most recent advances in technology. SPE analytes partitioning toward the organic contains the aqueous sample. The solvent isolates analytes using the same principles phase. The solvent is drawn off and saved, extracts the analytes as it passes through as those used in liquid chromatography, and the extraction step is repeated multiple the sample. The extract is collected in a though much less efficiently. As Figure 6 times. The solvent extracts are combined boiling flask and distilled, and fresh solvent depicts, in SPE, compounds are retained for the analytical step. For a basic discus- is sent to the top of the extractor to create and eluted as a mobile phase transports sion of liquid–liquid extraction, please see a continuous process. This process runs for them over a stationary phase (sorbent) that reference 6. 12–24 h, and it is used in situations in has been conditioned with an organic sol- Continuous liquid–liquid extraction (EPA which large sample sizes with low analyte vent to activate it. In the most common Method 3520C): This technique is an auto- concentrations are needed. The extract use of SPE, the mobile phase is the aque- mated version of the separatory funnel contained in the boiling flask is used for ous sample to retain the analytes onto the technique for a spectrum of non- and the analytical step. sorbent. This step is followed with a solu-

Circle 16 1126 LCGC VOLUME 19 NUMBER 11 NOVEMBER 2001 www.chromatographyonline.com bilizing solvent as the mobile phase to This technique’s benefits are that it sig- Water removal: Water is extremely polar elute the analytes, which are collected for nificantly reduces extraction times and sol- and will adversely affect most column analysis. vent consumption and has a concentration packing materials, especially GC stationary The SPE packing is housed in a car- step. With automated filtering systems, phases and some normal-phase HPLC tridge or disk. The cartridge is a disposable multiple samples can be processed simulta- packings. Therefore, analysts should syringe with a frit on each end of the pack- neously. The downside of SPE is the cost remove water from the extract before ing, and the disk is a membrane filter. The of the cartridges and disks. For a series of injecting it into the analyzer. A common smaller length-to-diameter ratio of a disk reviews of various aspects of SPE, please technique to remove any water from the allows greater flow and extraction rates rel- see reference 7. sample or extract is to pass it over anhy- ative to the cartridges. drous sodium sulfate. The sodium sulfate Postextraction Handling is a water scavenger, and it will dry the and Cleanup sample solvent without absorbing any of After the extraction step, chemists rarely the analyte of interest. Sodium sulfate perform analysis directly without further water removal usually is performed in con- (a) sample handling. Postextraction handling junction with a filtration step. The sodium Condenser includes steps as simple as sample–extract sulfate is added to the filter before filtering separation, water removal, and solvent the sample–extract mixture. Another exchange or a more involved, multiple- approach is to mix and swirl the sodium step cleanup. The cleanup methods are sulfate with the mixture solution before fil- Condensed designed to remove interferences that cause tration. solvent poor analytical results and increased analyt- Solvent concentration: This technique ical instrument downtime. Postextraction concentrates the analyte of interest, so the handling steps are dependent upon the analytical signal intensity is increased. This matrix, the analytes of interest, and the task is performed by evaporating the sol- solvent. vent to a 1–2 mL volume and then making Sample–extract separation: The objec- it up to a 5-mL volume in a volumetric tive is to separate the original matrix from flask or GC–HPLC vials. Automatic sol- Concentrated the extract. Two approaches are available: vent concentration systems are commer- solutes filtration and centrifugation. cially available. Filtration: The sample–extract mixture is Solvent exchange: This technique sepa- passed through a filter to remove the solid rates the extracted molecules by their sample from the solvent. Fresh solvent polarity to eliminate extraneous peaks in Solute solution washes the solid sample on the filter to subsequent analysis or to move the analytes ensure all the analyte goes into the col- to a different solvent that is more compati- Heating mantle lected solvent. Two or three wash steps can ble with the subsequent analytical tech- (b) be used with minimal solvent to prevent nique. Solvent exchange is performed as a Condenser further dilution. liquid–liquid extraction in a separatory Centrifugation: The sample–extract funnel. This step is one most analysts mixture is centrifuged, and the extract is would prefer to avoid. However, they may decanted and removed. The residual sam- need an aggressive solvent to extract the Condensed ple is washed two or three times with min- analytes from the matrix and remove extra- solvent imal solvent to prevent further dilution. neous analytes. Sometimes, a polar solvent

Solute solution (a) (b) (c) (d)

A A A I I AI IA Sample I A AI AI I I I I I AIA A A A I I I A Conditioning A AA Washing Eluting solvent solvent solvent Concentrated solutes A A Analytes A A A A A A A AA A AA SPE A AAA cartridge

I I I I I I I Collection I I II I I I Heating mantle I I I AA AA I I I I A AA reservoir I I I AAAA AA Interference Analytes Figure 5: Schematics of a continuous liquid– liquid extraction system in which the extraction solvent is (a) less dense and (b) more dense Figure 6: Steps in an SPE experiment: (a) sorbent conditioning; (b) sample loading; (c) washing, than the solution from which the solute is in which the analytes are retained and the interferences are washed into the collection reservoir; being extracted. and (d) elution, in which the analytes are eluted with a strong solvent. 1128 LCGC VOLUME 19 NUMBER 11 NOVEMBER 2001 www.chromatographyonline.com is necessary to remove the analytes of inter- points, acid–base partitioning to separate cleanup of nonpolar compounds such as est that can not be used in the chromato- acidic or basic organic compounds from organochlorine pesticides and PAHs. In graphic analysis. neutral ones, and oxidation of interfering addition to removing interferences, adsorp- The cleanup methods are covered by the components with acids, alkalis, and oxidiz- tion chromatography can be used to frac- 3600 series methods of SW-846 (see Table ing agents. tionate complex mixtures of analytes. II). They include adsorption chromatogra- Adsorption chromatography: This tech- Gel-permeation chromatography: This phy to separate compounds based on dif- nique is used to separate analytes of a rela- technique is used to remove high molecu- ferences in polarity, gel-permeation chro- tively narrow polarity range from interfer- lar weight or high-boiling-point interfer- matography to remove interferences with ing peaks of different polarity. Adsorption ences from the target compounds. High high molecular weights or high boiling chromatography is used primarily for the molecular weight compounds can contami-

Table II: 3600 series cleanup method summary

EPA Method Method Name Number (Technique) Objective Procedure Comments 3610B Alumina cleanup To separate analytes from Elute sample through basic- to Suitable for extracts that contain (adsorption interfering compounds of neutral-pH alumina with nitrosamines and phthalate chromatography) different polarity suitable solvents to leave esters interfering compounds on the column 3611B Alumina column To separate petroleum Elute sample through neutral-pH Not recommended for extracting cleanup and separation waste extracts into base– alumina with suitable solvents petroleum wastes with of petroleum wastes neutral aliphatic, to leave interfering compounds predominantly polar solvents; (adsorption aromatic, and polar on the column perform acid–base partition chromatography) fractions cleanup on extract before alumina cleanup 3620C Florisil cleanup* To separate analytes from Elute extract through Florisil to Suitable for extracts that contain (adsorption interfering compounds of leave interfering compounds on aniline and its derivatives, chromatography) different polarity or the column or cartridge or to chlorinated hydrocarbons, fractionate groups of fractionate target compounds haloethers, nitroaromatics, target compounds nitrosamines, organochlorine and organophosphorus pesticides, organophosphates, PCBs, and phthalate esters 3630C Silica-gel cleanup† To separate analytes from Elute extract through silica gel to Primary use is for extracts that (adsorption interfering compounds of leave interfering compounds on contain PAHs, derivatized chromatography) different polarity the column or cartridge phenolic compounds, organochlorine pesticides, and PCBs 3640A Size separation (size- To remove high molecular Elute extract through column Universal technique for exclusion weight, high-boiling-point packed with hydrophobic gels of semivolatile organic compounds chromatography) materials from target varying pore sizes to separate its and pesticides analytes components by molecular weight 3650B Acid–base partition To separate acid analytes Mix extract with methylene Useful for separating neutral PAHs cleanup (liquid–liquid from base to neutral chloride and water at pH 12–13 from acidic phenols; base–neutral partitioning) analytes in petroleum in separatory funnel; separate fraction may require an alumina waste extracts aqueous (acidic) and organic column cleanup before analysis (base to neutral) fractions 3660B Sulfur cleanup To eliminate sulfur from an Mix sample with either copper or Sulfur has solubility characteristics (oxidation and extract and prevent the tetrabutylammonium sulﬁte, similar to organochlorine and reduction) masking of organochlorine shake, and separate the sample organophosphorus pesticides; pesticides and organo- from the sulfur cleanup reagent typically used for sediment, phosphorus pesticides in marine algae, and industrial GC analysis waste samples 3665A Sulfuric acid– To decompose organic Exchange extracting solvent with Decomposes most other organic permanganate cleanup compounds that cause hexane, sequentially treat with chemicals, so it is not applicable (oxidation and baseline elevation or 98% sulfuric acid and, if for other target analytes reduction) complex chromatograms necessary, 5% potassium and prevent the accurate permanganate quantitation of PCBs

* Florisil is magnesium silicate with basic properties. † Sulfuric acid with sodium silicate. 1130 LCGC VOLUME 19 NUMBER 11 NOVEMBER 2001 www.chromatographyonline.com nate HPLC columns and be difficult to waste samples. Acid–base partitioning also Summary remove by washing. High-boiling-point can be used to fractionate base–neutral Sample preparation is a critical step in the compounds can contaminate GC injection compounds. overall process of obtaining reliable and ports and column heads, thus requiring Oxidation of interfering components: accurate data, especially in the environ- more instrument maintenance. Gel- Copper or tetrabutylammonium sulfite is mental analysis of nonvolatile and semi- permeation chromatography, also known used to eliminate the sulfur contamination volatile organic compounds. Extraction as size-exclusion chromatography, is the that can mask pesticide peaks in certain techniques are devised to remove a spec- most universal cleanup method for semi- GC detectors. Sulfuric acid and potassium trum of compounds. This removal requires volatile organic compounds and pesticides. permanganate are used to oxidize organic subsequent handling and cleanup of the Acid–base partitioning: This technique compounds that cause interferences for extract before analytical measurement. is used to separate neutral PAHs from the PCB analysis. Oxidation is a very rigorous In this “Sample Prep Perspectives” col- acidic PAHs that can appear in petroleum but nonspecific technique. umn, I attempted to review the extraction and cleanup techniques available to analysts according to SW-846 requirements for nonvolatile and semivolatile organic compounds. I have observed a noticeable improvement in sample preparation capa- bilities with SW-846’s inclusion of extraction techniques such as SPE for aqueous samples and pressurized-fluid extraction, SFE, and microwave extraction for solid samples. These newer methods reduce extraction times and solvent consumption.

References (1) S. Arment, Current Trends and Developments in Sample Preparation, LCGC 17(6S), S38–S42 (1999). (2) R.E. Majors, Current Trends and Developments in Sample Preparation, LCGC 17(6S), S8–S13 (1999). (3) B.E. Richter, Current Trends and Developments in Sample Preparation, LCGC 17(6S), S22–S28 (1999). (4) G. LeBlanc, Current Trends and Developments in Sample Preparation, LCGC 17(6S), S30–S37 (1999). (5) J.M. Levy, Current Trends and Developments in Sample Preparation, LCGC 17(6S), S14–S21 (1999). (6) R.E. Majors, LCGC 14(11), 936–943 (1996). (7) R.E. Majors, Current Trends and Developments in Sample Preparation, LCGC May 1998, S8–S15 (1998).

Greg LeBlanc is the new business development manager at CEM Corp., P.O. Box 200, Matthews, NC 28106-0200, e-mail [email protected].

Ronald E. Majors “Sample Prep Per- spectives” editor Ronald E. Majors is business development manager, con- sumables and acces- sories business unit, Agilent Technologies, Wilmington, Dela- ware, and is a mem- ber of LCGC’s editorial advisory board. Direct correspondence about this column to “Sample Prep Perspectives,” LCGC, 859 Willamette Street, Eugene, OR 97401, e-mail lcgcedit@ lcgcmag.com.

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