JOURNAL OF RESEARCH of the National Bureau of Standards-A. Physics and Chemistry Vol. 68A, No.6, November- December 1964 Absolute Isotopic Abundance Ratio and the Atomic Weight of Bromine Edward 1. Catanzaro, Thomas 1. Murphy, Ernest 1. Garner, and William R. Shields

(August 4, 1964)

An absolute value is obtained fisotopes. The res ultin g absolute 13r 79/13r81 ratI,D, IS 1.02784 ± 0.00190 which yield s an atomic weight (CI2 = 12) of 79.90363 ± 0.0009.2 . . I he l.Ildlcated uncertainties are overall limi ts of error based on 95 percent con­ fid ence lunlts for t he mean and allowances for t he effects of known sources of possible sys­ tematIC error plus a coml?onent to cover possible natural variations in isotopic composition a lthough no provable varIatwns were noted among t il e 13r 79/13r81 ratios of 29 commercial and naturlll samples. Mass s pectr?metric determinations of the atomic weights of bromine and sil ver gIve a combining weight ratio of Ag13r/Ag = 1.740752.

1. Introduction known isotopic composition, prepared from nearly p~re separated bromine isotopes. The measured .The atomic weights of silver, chlorine, and bro­ bIases were then used to obtain the absolute Br79/ BrB1 ratio of a reference sample of commercial so­ mme form the classical basis for establishino . atomic weights of many of the elemen ts. Rece~1t mass dium bromide. In addition, the Bri9/BrB1 ratios of a spectrometric determinations of the atomic weio'hts number of sR.mples of commercial purified bromine and bromide from brines and minerals were also of silver [1) I and chlorine [2) have yielded valu:s of measured. 107.8682 ± O. 0010 2 and 35.45273 ~ ~:~~~~~ ~ re- spectively. The present work extends the study to 2. Experimental Procedure bromine. A number of mass spectrometric determinations 2.1. Mass Spectrometry ?f bro~ine isotopic abundances have been reported m the hteratme. Blewett [3), Williams and Yuster All is?topi? meas~rements were made using two [4), White and Cameron [5), and Cameron and nearly IdentlCal sohd-source single-focusing mass Lippert [6) used electron bombardment ion SOUl"ces spectromet,ers equipped with 68-deg analyser tubes, 60-deg magnet pole pieces and 12-in. radii of curva­ and obtained values of Br79/Br8 1 = 1.026 ± 0.026, 1.021 ::J;: 0.004, 1.0210 ± 0.0020, and 1.0217 ± 0.0002, ture. Triple-filament rhenium. ribbon (1 X 30 mils) respectIvely. However, none of these studies in­ sources were used and ion currents were measured by cluded a direct meaSUl"ement of instrumental bias means of a vibrating reed electrometer with an and, therefore, the resulting ra,tios were not absolute. expa~lded-scale reco~~ der. Ratios were measured by White and Cameron (5) recognized that discrepancies varymg the magnetIc field at constant ion-accelerat­ between observers and instruments were probably ing voltage. due to mass discrimination OCCUlTing in the ion . The bromide was d~posited on the sample filaments lenses of the sources, but were unable to meaSUl·e or III the form of ammomacal solutions of silver bromide. correct for this discrimination. Cameron and Lip­ Preliminary experiments showed that AgBr was far superior to N aBr with respect to signa.! stability pert [6) took care to avoid fractionation dmino· the chemica.l pr e para~ion of their samples, but "'only during the mass spectrometric analyses. One drop asserted that thmr method of measmement sub­ of a AgBr solution containing 3 mg Br/ml (",,0.06 limation of sodium bromide, was free of any instru­ mg Br) was deposited on each filament and dried u~de!' meJ?-tal (!iscrimil~ati~n. They did not attempt to il: hei!'t lamp. To minimize the variability of dlscnmmatIOn, all analyses were made in an identical venfy thIS assertIOn lt1 any manner. manner. A strict pattern of fil ament heating was In th~ present stu~y , both mass spectrometers were cahbrated for bIas by the use of sampLes of followed and a set of 10 measurements was made on a growing signal (3-5 X 10- 13 A) between 38 and 52 min after the filaments were turned on. Analyses ! Figures i~l ~~ack e t s indicate the literature references at t he end of this paper. which did not follow the normal signal-growth pat­ ~ Overalllnlllt of error based on 95 percent confidence limits for the l11can and allowances ror effects of known sources of possible systelnatic error. tern were discarded. 593 2 .2. Puriiication of the Se para ted Isotopes hydrogen peroxide was ~ecomposed . This oxi~a­ tion by hydrogen perOXIde rem.oved any cya!lIde Electromagnetically separated isotopes in the form [10] or thiocyanate [11] that mIght ha-ye dIst~l~ed of sodium bromide were obtained from the Isotopes with the bromim'. Tpsts, based on the msolubIhty Division Oak Ridge National Laboratory of the of silver cyanide and silver thiocyanate, showed that Union Carbide Nuclear Company. The NaBr79 soluLions prepared in this manner contained less th~n and the N aBr8! were designated Series LM, Lot 0.001 percent (CN)- or 0.001 percent (SCN)- 111 Number 1391(a) and Series LM, Lot Number terms of the N aBr present. . 1392 (a), respectively. The. ce!tificate o.f analysis The solution was then transferred to a platmum accompanying each sample mdlCated a hIgh de~ree dish and evaporated to dryness. The dish and con­ of cationic purity but did not exclude ~he pos~Ible tents were covered and heated to 550 DC for } ~ hI' presence of other halides .01' pseudo~ahdes. Smce in an electric furnace to convert any bromate present the bromide ion concentratIOn of solutIOns was to be to bromide. Any nitrate present would be converted determined by silver coulometry and si~ce the hali~es to nitrite and cause difficulty in the bromine titration. iodide and chloride and pseudo-halIdes, cyamde Therefore the salt mixture, which contained sodium and thiocyanate, w~uld reac~ with. silver to form bromide 'sodium nitrite, and the excess sodium insoluble compounds [7], the IOStoplC sampl~s were carbonate, was dissolved in 50 ml of H 20 and 1 drop further purified to insure the removal of these of phenolphthalein indi?ator solution was adde~ . impurities. The solution was neutralIzed to the phenolphthalem Each separated isotope sample (abou~ 5 g) .was end point with (1: 9) acetic acid. An equivalent divided in half and treated as follows: 'Ihe sodmm amount of tbe dilute acetic acid plus a 1-ml excess bromide (about 2.5 g) was dissolved in a small amoU?t was then added to neutralize the bicarbonate pro­ of water and transferred to a 300 ml three-neck dIS­ duced and make tbe solution slightly acid. Two tilling apparatus like that described b:y Murphy, milliliters of 30 percent hydrogen peroxide was then Clabaugh, and Gilchrist [8]. The solutIOn ,:"ol~me added and tbe solution was heated overnight on a was increased to 100 ml and 0.2 ml of redIstIlled steam bath. Under these conditions nitrite is oxi­ nitric acid was added. Twenty milliliters of dilute dized to nitrate [12] and the prolonged heating ammonium hydroxide (1.: 9) was added to the destroys the excess peroxid.e.. . receiver flask. The solutIOn \vas then heated. to Analyses of sodium bromIde solutIOns prepare~ m boiling, and refluxed for 2 hI' while a st,ream of halIde­ the above manner have shown that the solutIOns free air was drawn tln'ough the system. The h~at contained less than 0.0005 percent bromate ion, was then increased and about 10 ml of th~ solutIOn less than 0.0005 percent nitrite ion, and less than was distilled into the dilute NH40H solutIOn. 0.0005 percent hydrogen peroxide in terms of the This procedure wil~ oxidiz~ iodide to iodine [9] and sodium bromide present. Tbe brOl;nate tes~ w~ s remove it from solutIOn whIle only a small amount based on the reaction of bromate WIth bromIde III of bromide is lost. Tests based on the insolubility acid solution to produce bromine whi.ch was. detected of silver iodide in ammoniacal solution have shown with o-tolidine. Nitrite was determmed WIth phen­ that when 0.025 mg of iodide ion was added to a ylenediamine [~3]. Th.e test. for ?yd~'ogen p~roxide solution containing 2.5 g of NaBr and treated as was based on Its reactIOn wItb titamum to form a above, the recovery of io~in~ was complet~, s~ that colored complex [14]. in terms of the NaBr the IOdme concentratIOn m the This purification procedure was r:peated on the solution would be less than 0.001 percent. Tests remaining portions of the separated Isotope samples based on the insolubility of silver cyanide have al~o for groups II. . . . shown that if cyanide were present, almost ~ll of It Iodide was not detected m eIther of the startmg would be removed by the above procedure either as isotopic samples. Chloride was found in both the hydrogen cyanide or as cyanogen. . . NaBr79 and the NaBr8! to the extent of 0.13 percent Ten milliliters of water and 20 ml of redIstilled and 0.11 percent, respectively. As stated previously, nitric acid were added to the sodium bromide solu­ tests have shown that the purification procedure tion and the solution was refluxed while a stream of reduced the chloridc con ten t of the sodium bromide halide free air was drawn through the solution. to less than 0.001 percent. Cyanide and thiocyanate The bromine liberated was slowly distilled into a were not determined, but if they had been present solution containing a 20 percent excess of the stoichi­ originally, the concentration of each would have been ometric quantity of sodium carbonate and 5 ml of reduced to less than 0.001 percent. 30 percent hydrogen pero~ide. The distillati?n was continued until only a slIght color of bromme re­ 2.3 . Preparation and Bromide Concentration of mained in the distilland. Separa ted Isotope Solutions Dilute nitric acid (1: 5) has been shown to oxidize bromide to bromine quantits.tively [8] without oxi­ The solutions of the purified N aBr79 and N aBr8! dizing chloride to chlorine. Chloride analyses .l8] were filtered and transferred to 100 ml volumetric of the distillands after removal of the bromme flasks whose necks had been cut off so that only about showed that the chloride concentration was less 1 cm remained. The solutions were diluted to about than 0.001 percent in terms of the NaBr present. 65 ml and thoroughly mixed by swirling the fla ~ks After the distillation of bromine was completed, for several minutes. Each flask was then sealed WIth the distillate was heated on a steam bath until the a rubber serum septum and allowed to stand over- 594 night in the case of a semi-microbalance to insure therefore 2.37 X 10- 5 meq. Brig solution and that of thermal equilibrium. The fl asks and contents were five determination s is 2.12 X lO- 5 meq. Brig solution. then weighed on the balance to ± 0.02 mg. Samples were withdrawn from each flask: by inserting a stain­ TABLE la. Groups I less steel needle attached to a glass hypodermic syringe through the rubber septum and withdrawing Sample No, I Wt. Sol I Bromide I Cone Br the desired amount of solution. A second needle which just punctured the septum served as a vent. Concentration of bromide iOIl in NaHr n solution The syringe and needle were then washed with dis­ g meg. m eg, Brig Sol tilled water and the washings were combined with the A ______._._ 7.53019 2, 56406 0. 340504 B . ______8.21278 2. 79583 . 340424 bulk of the sample. The weight of the sample C _. ______._ D ______8.54475 2. 90845 , 340379 withdrawn was determined from the weight of the E ___ _. ___ . __ _ 8.26555 2, 81273 .3'10296 flask before and after the withdrawal of solution. 7, 77453 2. 646J 8 .340365 Four samples of from 7 to 9 grams each were with­ MealL ___ _. ______drawn from each solution by this method. The ' , 3'10394 quantity of bromide in each of these samples was Concentration of bromide ion in NaBr81 sol ution from 2 to 3 meq. Each sample was transferred to a A . ______100 ml beaker and the syringe and needle were 9. e9645 2. 97587 0. 327J46 B . ______._ ._ 8.65398 2. 83156 . 327J97 washed with distilled water, the washings being C ______. _._ 8. 07874 2, 64328 . 327190 caught in the beaker with the bulk of the aliquot. D . ______._ 7. 817J 2 2. 55753 . 327170 The volume was adjusted to about 15 ml by evapora­ lVlean . ______tion on a steam bath. ', 3271 76

The bromide ion concentration of each solution a ~ e l l C standard error of the mean is estimated to be was determin ed by constant-current coulometry 0,000024 m eq/g sol. for the group with four analyses an d 0.000021 for the group witb fi ve analyses, based 011 se ven using electrically generated silver ions. The end groU I)S of data including the sets shown here. point or the silver titration was determined ampero­ metrically. The details of the method arc described TABLE lb. Groups II by Marinenko and Taylor [15]. This procedure was first applied to solutions pre­ Sample No. 1 Wt. Sol I Bromide I COll e Br pared from sodium bromide low in iodide and chloride. This sodium bromide was prepared in our Concentration of bromi de ion in NaBr 7 ~ soluLion laboratory since all of the commercially available g nuq. meg, Brio Sol sodium bromide was found to bE' high in chloride A . ___ . ______. 7. 77 112 2.810027 0. 36J599 "B ______._ .. 7.88535 2.851350 . 36J60 1 content. An excess of redistilled bromine was re­ C ____ . ______7, 32444 2. 64 8832 .361 643 acted with sodium carbonate solution. The resulting D __ . _. ______7,73096 2. 795487 . 361596 solution was evaporated to dryness and the mixture of sodiilln bromide and sodium bromate was heated Mean. ______. ______' .361610

to 550 DC to convert the bromate to bromide. The Concentration of bromi de ion in NaBr81 solution sodium bromide was then [used by heating in dry nitrogp.n to about 800 DC in a tube furnace. The A ____ . ______. 7, 78525 2.74700 0. 352847 C . ___ . ______7. 78655 2. 6768 2 . 3528 38 iodide and chloride content or this NaBr was found D ______7.09924 2. 5[502 . 352857 to be less than 0.001 percent. E . ___ . ______7.47154 2.63715 . 352959 Three solutions o[ sodium bromide were preparp,d in the approximate concentration of the isotope solu­ Mean. ______. ______. __ ' . 352875 tions. Five to six samples each con taining from 2 to a '"l'be standard error of the lucan is estimated to be 3 meq. of bromide ion were withdrawn from each 0,000024 m eq/g sol. based on seven groups of data in clud­ solution and analyzed for bromide ion by the ing the sets shown here. described method. Data resulting from the analyses of these three 2.4. Isotopic Analyses of the Solutions of the prelin1inary bromide solutions showed that: (a) The Separated Isotopes meq. of bromide ion found by this method agreed to within 0.1 percent of the meq. calculated, and the To avoid memory problf'ms, one of the two assayed percentages were independent of sample solutions of the sepiLriLted isotopes was aniLlyzed on size and concentration; and (b) The analyses of the one mass spectrometer iLnd the other solu tion on three solutions were of equal precision. the other mass spectrometer. The sources were dis­ The results of the bromide analyses of the separated mantled and thoroughly clea ned before nnd after isotope solutions are shown in table 1a for Groups I each series of measurements. Blank annlyses showed and table 1b for Groups II. Pooling the results of that clean sources yielded no bromine signals. these four sets of analyses with the three described The isotopic compositions of the separated isotope above yields a value of 4.74 X lO - 5 meq. Brig solu­ solutions are given in table 2. The respective Br79 tion as the standard deviation for an individual and Br81 isotopic compositions as reported by ORNL determination (2 7 degrees of freedom). The stand­ are: "Br79", 99.74 ± 0.02 atom percent B1' 79 , 0.26 ard error of the mean of four determinations IS ± 0.02 atom pel'cent Br81 ; "Br81 ", 0.38 ± 0.02 atom 595 percent Br7Y , !H:l.62 ± 0.02 atom percent Br 81. The where ORNL limits quoted express the precision of the gl =meq. Br from Br79 soln meaSUl·ements. From known sources of systematic g2=meq. Br from Br81 soln error, the absolute error is estimated by ORNL to .II =mole fraction of 81 in Beg soln = 0.00264 be less than 1 percent. (l-jl) = mole fraction of 79 in Br79 soln = 0.99736 j2=mole fraction of 81 in Br81 soln = 0.99614 (1-j2) =mole fraction of 79 in Br 8! soln =0.00386.

TABLE 2. Isotopic composition The values of 9 and }J. are tabulated in table 3a for of separated bromine isotopes group I and in table 3b for group II. used in calibration samples

Isotope Isotopic COlllpositioD II. TABLE 3a. Group I -composition of calibration samples (atom %)

Calibration NaDri 9 so lution NaBr81 solution Isotopic :l3r"______Br79=99.736 sample No. ratio Br" = 0.264 ±0.008

Br"______:l3r 79 = 0.386 ± 0.008 meq. Br meq. Br :l3r"=99.614 wt 801 Yl wt sol Y2 JJ. L ______2. 20305 0.749905 2.23035 0.729717 1. 03000 3 ______2.03553 . 692882 2.08166 . 681069 1. 01972 4 ______II. The limits express the Inax illlU111 2.07995 . 708003 2.11262 .691199 1. 02666 uncertainty as estimated from tbe 95 5 ______2.11338 . 719382 2. 11904 . 693299 1. 03992 percent confidence limits of the mass 6 ______2.17520 . 740425 2.24607 . 734860 1. 00999 spectrometric dctermulatiolls and possi­ I ble errors in tbe correction factors.

TABLE 3b. Group II- composition of calibration samples

2.5. Preparation of the Calibration Samples Calibration NaBr79 solution Nanr~ l solution Isotopic sample No. ratio Six calibration samples were originally prepared meq. Br meq. Br (group I), but the results of sample No.2 were subse­ wt sol ljl wI sol Y2 JJ. L ______I. 04618 0. 378309 1. 08450 0.382693 0. 99104 quently discarded when the mass spectrometric 2 ______1. 09963 .397637 1. 09671 .387002 1. 02982 data did not conform to the general pattern. In 3 ______I. 09990 .397735 1. 10046 .388325 1. 02658 4 ______I. 09030 . 394263 1. 09721 . 387178 1. 0206R view of this it was considered desirable to prepare 5 ______I. 18382 .428081 1. 07291 .378603 1. 13256 a completely new set of six calibration samples 6 ______1.10534 .399702 1. 20550 . 425391 . 94230 (group II). All calibration samples were prepared by mixing portions of the Br79 and Br81 solutions, which were 2.6. Isotopic Analyses of the Calibration Samples withdrawn and weighed in the manner already Although the bromine background signals were 7g 81 described. The ratios of Br /Br ranged from 1.01 completely negligible during the analyses of natural to 1.04 for gTOUp I and 0.94 to 1.13 for group II. samples, slight memory effects became evident dur­ For each determination, the portions for the cali­ ing the analyses of the calibration samples. These bration samples and the samples for the determina­ samples were run alternatingly with the reference tion of the bromide concentration were withdrawn sample and memory effects on the order of 0.2 per­ on the same day with the exception of sample E of cent were evident when the calibration sample the Br79 solution of group I and sample E of the differed by 10 percent from the reference. To Br81 solution of group II which were withdrawn two eliminate memory, a uranium sample was run before days after the rest of the group. and after every sample that differed from the refer­ Each calibration sample was thoroughly mixed by ence by more than 1 percent. The very high tem­ stirring and 0.5 ml of nitric acid was added. Twenty perature achieved during the uranium runs served milliliters of 0.1 N AgN03 solution were added to to remove any bromine from the previous analysis. precipitate the bromide as silver bromide and the solution was allowed to stand overnight in the dark. 2.7. Natural and Commercial Samples The solution was filtered through filter paper and the precipitate of silver bromide was washed with The reference sample is a commercial sample of dilute (1:500) nitric acid. The paper was carefully sodium bromide designated as NBS Isotopic Refer­ folded over the precipitate and both were dried in ence Sample No. 106. A portion of this sample was an electric oven at 110 °C. A weighed portion of the converted to silver bromide in the same manner as silver bromide was then transfened to a 4 ml screw­ the calibration samples. cap vial and sufficient concentrated ammonium The samples of commercial bromine were reacted hydroxide was added so that the resulting solution with ammonium hydroxide solution and converted contained 3 mg of bromide per n1.illiliter of solution. to silver bromide in the same manner as the cali­ The isotopic ratio, }J. , of each calibration sample bration samples after making the solutions acidic was calculated from with nitric acid. The sylvites (KCl) , carnallites (KMgC13·6H20 ) , gl (1-.I1) + g2 (1-j2) brines, sea water, and bittern were treated as fol­ gli!+gdz lows: A measured quantity was dissolved in 500 ml 596 TABLE 79 sl of H 20 and 1 ml of nitric acid was added. The solu­ 5. Ob served and corrected values of the Br /Br ratio tion was transferred to a distilling apparatus and, f or the reference sample' to remove iodine, 50 ml of the solution was distilled Observed Correction Corrected ratio into dilute ammonium hydroxide solution. Seventy­ ratio factor five milliliters of nitric acid were then added and the bromine produced was distilled into dilute am­ Group I M S-l 1. 028792 0.9990390 1. 02 7807 monium hydroxide. Since chloride was the dominant M S-4 1. 029592 .9985416 1. 028090 halide in these samples, it was necessary to repeat Group II M S- l 1. 02 7683 .9999 66 1. 027669 the oxidation and distillation to free the bromine M S-4 1. 029675 .9981807 1. 027803 from chlorine. The bromide concentration in most Mean ______• ______.•. _. ______1 1. 02784 ±O. OOlO5' of these samples ranged from 0.01 percent to 0.1 percent. After the second distillation, the solution a Uncertainty components: was made acidic with nitric acid, converted to silver 95 percent confidence limits on ratio determination .. ___ • ______±0. 00051 Possible error in composition of separated isotopes ______±O.000:33 bromide, and the bromide ion concentration adjusted Possible error in calibration sampies ______± 0.00021 to 3 mg Br/ml, as in the case of the calibration samples. The bromyrite sample (AgBr) was dissolved in Table 6 summarizes the bromine isotopic-ratio ammonium hydroxide and the silver was electro­ measurements of samples of commercial bromine and deposited onto a platinum gauze electrode. The the original bromine source material as supplied by seven major bromine manufacturers in the United solution was made acidic and treated as the above States. Table 7 summarizes the results of measure­ minerals. ments on a number of mineral samples. The results 3. Results and Discussion show that there are no significan t isotopic variations among any 01' the commercial and natural samples. Table 4 compares the calculated isotopic ratios of The average Br79/Br8l ratio of the 29 samples is dis­ 11 calibration samples with the results obtained on placed from the re/'erence by - 0.00048. Most of the two mass spectrometers. Two groups of calibra­ this shift is due to the mineral samples which yield tion samples were prepared and the sources of both the lowest ratios. This result is consistent with pre­ instrumenLs were dismantled and cleaned between vious experience at this laboratory on other elements. the analyses of the two groups. Table 5 shows the It may be attribu ted to a difference in purity between results of multiple analyses of the reference sample the mineral samples and the reference. In general (12 per mass spectrometer per determination), both it is more difficult to obtain standard intensity levels uncorrected and corrected for the biases indicated during mass spectrometric analyses of natural sam­ by the calibration samples. The reasons for tIle ples as compared to reference samples [1] and it was differences in bias cannot be quantitatively evalu­ observed that the Br79/Br81 ratios obtained in the ated, but the major effect appears to be due to slight more difficult (higher filam ent temperature) analyses changes in the alinements of the source parts when were consistently lower than LllOse obtained in the they are reassembled after cleaning. In any case, less difficult (lower filament temperature) a nalyses. the excellent agreement b etween all four corrected values of the reference indicates that the calibration T A BLE 6. I sotopic abundance l'alios of bl'omine from val'ioll s method is consistent. commercial bromine and bromine source mate1'ials re lative to reference sam ple

TABLE 4. Determination of mass spec tTOmetric bias A verage observed I sotopic ratio, Br"/BrSI Correction factor (calc/M .S.) Sample So urce ratio of Calibration ------,------,--·---1------.----­ r aLios a sample No. Calc. 1'v1 S-1 1\1 S-4 M S-l M S-4 Brine, Searles Lakc ______A'illcrican Potash & Chemical O. 9088 Corp. Group I Brine______Arkansas Chemical Co ______.9996 Bromine______Arkan sas Che w ical Co ______.9995 Monroe brine ______Dow Chemical Co ______.9994 L ______1. 03000 1. 02970 1. 03035 1. 000301 0. 999670 Midland bromine, purifled ______Dow Chemical Co ______. ____ _ . 9098 3 ______1. 01972 1. 02055 1. 02120 0. 999197 . 998561 4 ______1. 02666 1. 02820 1. 02865 .998512 . 998075 Freeport bromine, purified ._____ Dow C bem ical Co ______.9995 5 ______1. 03992 1. 04105 1. 04125 . 998915 .998723 Sea Water ______Etbyl-Dow C hemical Co ______. .9992 6 ______1. 00999 1. 01175 1. 01235 . 998270 .997679 Bittern __ .______F . J\l . C. Corp ______.99\)4 Bromine ______.. F . Nt. C. Corp ______.9990 Brine ______Great L akes C bemical Corp ____ _ .9999 Mean ______- _-- ___ ------.9990390 . 9985416 Brine ______Great Lakes C hcmic" l Corp ____ _ .9998 Brine ______Ureat L akes Chemical Corp ____ _ 1. 0005 G roup TI Brinc ______Great L nkes C hemical Corp ____ _ 0. 9998 BrOTIline______Great L akes C hrlll icnl ('orp ____ _ . 9999 Bronline ______Great L akcs Chclllical Corp _____ .9998 L ______0.99104 0.99115 0.99270 0.999899 0.998328 2 ______1. 02982 1.02960 1. 03225 1. 000214 . 997646 Bromine ______Great L akes C hemical Corp ___ ._ I. 0002 3 ______1. 02658 1. 02735 1. 02875 0.999260 .997900 ]3romine ______Great L akes C helllical Corp ____ _ 0.9998 4 ______1. 02068 1. 02125 1. 022 70 .999442 . 998025 Brine, St. Louis produetion _____ :Michigan Chell1 ical Corp ______I. 0002 5 ______1.132.\6 1. 13185 1. 13425 1. 000627 .998510 Bromine, St. Louis prod uetion __ Michigan Chemical Corp ______1. 0000 6 ______0.94230 0.94185 0.94355 1. 0004 78 .998675 Bromine, :Manistic prod uction __ ~1ic hi ga n C hemical COl'p ______0. 9994 Bromine, El Dorado producLioll _ IV[i chiga n C hemical COl'P ______. 9992 M.can ______------. 9999866 .9981807 • ( I1r"/Br81) sample/(Br"/BrSl ) reference. The 95 percent confidence limit is ±0.0012.

597 TABLE 7. I sotopic abundance mlios of bromine from some ± 0.025. The uncertainties are the sum of the 95 minemls relative to reference sample percent confidence limits on the ratio determination and the estimated maximum possible errors in the Average obser ved analyses of the separated isotopes and the composi­ Sample No." Description ratio of ratios b tions of the calibration samples. Using the nuclidic masses given by Everling et al. [16], the results yield 62416 ____ . ______Carnallite, Stassfurt, Germany ______0. 9992 an atomic weight of 79.90363 ± 0.00051 on the 98011. ______Carnallite, Barcel\ona, Spain ______. 9990 106869 ______Carnallite, New M exico ______. . 9997 unified scale (CI2= 12). These calculations are ]03518 c ______Sylvite, Nebra Germany ______t . 9990 summarized in table 8 where the error statements 103518 ' . ______Sylvite, Nebra, Germany ______.9988 92665 ______Sylvite, New Mexico______. ______. 9995 include the effect of possible natural variation to the 93472 ______Sylvite, Kalusz, Galccia, Poland ______. 9993 80263 ______Bromyrite, Broken Hill, Anstralia ______. 9990 extent noted previously . The atomic weight of bromine reported here is "U.s National Museum Catalog numbers. significantly different from that accepted by the b (Brro/BrSI) sample/(Br"/BrSI) reference. The 95 percent confidence limit is ± 0.0012. International Commission on Atomic ",Veights (1961 ), o Two pieces frOln the saUle smnple. 79.909 ± O.002 (C12= 12), which was derived by the use of a combining weight for AgBr/Ag = 1.740785 The possibility of slight isotopic fractionation and the Commission's value of 107.870 for the atomic dming the extraction of the trace amounts of bromi?e weight of silver. Using the herein determined value in the natural samples cannot be completely dIs­ of 79.90363 for bromine and the silver value of carded, but is considered extremely unlikely in view 107 .8682 from Shields et al.[l] gives a combining of the high recovery techniques used. weight ratio AgBrjAg= 1.740752. Table 9 sum­ A term to cover a possible natmal variation of marizes the atomic weight results on silver, chlorine ± 0.00085 (the range of results for the natmal and bromine obtained in this laboratory using the samples) in the Br79 jBr81 ratio has been included in same mass spectrometers and the same calibration the error attached to the final atomic weight value technique. Also shown are the calculated com­ (tables 8 and 9). bining weight ratios of AgCl/Ag and AgBrjAg. The absolute ratio, Br79/Br81 = 1.0274 ± 0.00105, for the refererence sample results in the percentage abundances: Br79=50.686 ± 0.025 and Br81= 49.314

TABLE S.- S ummary calcu lation of the atomic weight of bromine The authors are indebted to George Marinenko for the coulometric titrations of the bromide in the Absolute isotopic ratio ______Br "/Br81 = 1.02784 ± 0.00190 " separated isotope solutions and to Hsein H. Ku for A bsolute isotopic composition, Atom percent- Br79=50.686 ± 0.047 " the statistical analysis of the experimental data. c: Br8!=49.314 ± O.047 " They also express their appreciation to Dr. Geo~ge N nclidic m asses (CI'=12) ______Br79=78 .91 8348 ± O.000019 b Brsl =80.91 6344 ± O.000037 b Switzer and the U. S. NatIOnal Museum for supplymg the mineral samples and to the following companies Unified atomic weight (CI'=12) ______=79.90363 ± 0.00092 Uncertainty components: for supplying the bromine and brine samples : Reference ratio determination ______=±0.00025 Composition of separated isotopcs ______=±.0001 6 American Potash & Chemical Corp., Los Angeles, Composition of calibration samples ______=±.00010 Calif.· Arkansas Chemicals, Inc., EI Dorado, Ark.; P ossible natural variations ______=±.OOO41 TotaL ______-- ___ _ =±.00092 The Dow Chemical Co., Midland, Mich. ; Ethyl­ Dow Chemical Co. , Freeport, Tex. ; F . M. C. Corpo­ " The uncertainties are overall limits of error based on 95 percent confi dence limits for the m ean and allowances fo r the effccts of known sources of possible ration, Newark, Calif. ; Great Lakes Chemical Corp., system atic error (See table 5) plus a component (. 00085, in the r atio) to cover Filer City, Mich.; Michigan Chemical Corp., Saint possible n atural variations in the Bri9/BrS! ratio. b From ref. [16]. Louis, Mich.

TABLE 9.-Summary of National Bureau of Standards mass spectrometric atomic weight determinations (0 12 = 12) of snver, chlorine and bromine

Elemcn t Absolute isotopic ratio Nuclidic mass a. Atomic weight

Ag b ______Agl 07/AgI O'= I .07597 ± 0.OOI35 AgI07 = 106.904970 ± 0.0001i0 107.8682 ± 0.001O Agl09= 108 .904 700 ±0.0001i0 CI , ______Cl"jCl37 =3.1272 +0.0079 CI" = 34.9688545 ± 0.0000028 35 .45273 + 0.00092 -0.0082 - 0.00097 CI37 = 36.9658959 ±0.0000022 BL ______Br"/Br'l = 1.02784 ±0.00190 Br" = 78.918348 ± 0.00001 9 79.90363 ±0.00092 Br" = 80.916344 ± 0.00OO3 7

Calcnlated combining weight ratios: AgCljAg AgBr/Ag 1.328667 1.74 0752

" See referen ce [16]. b See reference [1] . o See reference [2] . 598 (9] E. Abel, Monatsh. 81,339 (1950) . 4. References (10] O. Masson, J. Chem. Soc. 91, 1449 (1907). (1] W. R. Shields, E. L. Garner, and V. H . Dibeler, J . Res. [11] F. Schuster, Z. anorg. allgem. Chem. 186, 253 (1930). NBS 66A (Phys. and Chem .), 1 (1962). [12] E. Halfpenny and P. L. Robinson, J . Che l11. Soc. 1952, (2] W . R . Shields, T. J. Murphy, E. L. Garner, and V. H. 928. Dibeler, J . Am. Chem. Soc. 840, 1519 (1962). [1 3] R . Uzel, Coil. Czech. Chem . Commun. 5, 139 (1933). (3] J . P . Blewett, Phys. Rev. 40 9, 900 (1936). [14] N. Allen, Ind. Eng. Chem., Anal. Ed. 2, 5.5 (1930). (4] D. Williams and P. Yuster, Phys. R ev. 69, 556 (1946). [15] G. Marinenko and J. K Taylor, J . Res. NBS 67A (Phys. (5] J. R. White and A. E. Cameron, Phys. Rev. 74, 991 and Chem.), 31 (1963). (1948). [16] F. Everling, L. A. Konig, J . H. E., iVIattauch, and A. I-I. (6] A. E. Cameron and E. L. Lippert, Jr., Science 121, 136 Wapstra, N uclear Phys. 18, 529 (1960). (1955). (7] W. F. Hillebrand, G. E. F. Lundell, H . A. Bright, and J . 1. Hoffman, Applied Inorganic Analysis, 2d eel. , p. 726 (J ohn 'Wiley & Sons, New York, N.Y., 1953). (8] T . J . Murphy, W . S. Clabaugh, and R. Gilchrist, J. Res. NBS 53, 13 (1954). (P aper 68A6- 306)

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