The precision of the analytical data has been evaluated for those nuclides for which a statistically significant number of assays has been performed. For this purpose, data obtained in replicate analyses for some of these nuclides in a set of 35 samples have been employed. Two criteria were used to select data for evaluation of the precisions: The net counting rate in the individual assay sample was greater than 5Oy0 of the counter background, and a minimum of six sets of replicate assays, satisfying the first criterion, was available for a given nuclide. Analytical data, which fulfilled these two criteria, have been obtained for nine nuclides: P32,P5,1W4,Fe59,Co5*, CoB0, ZrP5, Se7j, and Sr9'3. The precision, a t
the !%yo confidence level, was calculated for each set of replicate analyses for the respective nuclides. The value of the mean precision for each nuclide is shown in Table I with the number of sets of replicate assays from which the mean value was derived. The values vary from a minimum of 3.4y0for Fe59 to 5.2y0 for ZnG5. These precisions are deemed adequate for most applications for which these procedures may be used. LITERATURE CITED
(1) Bate, L. C., Leddicotte, G. W.,eds., Natl. Acad. Sci.-Natl. Research Council R e p t . NAS-NS-3041 (1961). (2) Beard, H. C., ed., Zbid., NAS-NS-
3002 (1960). (3) Finston, H. L., Kinsley, M. T., eds., Zbid., NAS-NS-3035 (1961).
(4) Hicks, H. G., ed., Zbid., NAS-NS-3015 (1960). (5) Koch, R. c., Grandy, G. L., ~ ~ N A L . CHEM.33,43 (1961). (6) Leddicotte, G. W., ed.,, N a f l . Acad. Sa.-Natl. Research Counczl Rept. NASNS-3018 (1960). (7) LeddicdGe,. 6. W., ed., Ibid., NASNS-3030 (1961). (8) Leddicotte, G. W., ed., Ibid., in publication. (9) Leddicotte, G. W.,ed., Zbid., NASNS-3054 (1962). (IO) Maeck, W. J., ed., Ibid., NAS-NS3033 (1961). (11) Nielson, J. hf., ed., Ibid., NAS-NS3017 (1960). (12) Steinberg, E., ed., Zbid., NAS-NS3011 (1960). (13) Sunderman, D. N., Townley, C. W., eds., Ibid., NAS-NS-3010 (1960).
RECEIVEDfor review June 19, 1961. accepted December 11, 1961.
Radiochemical Determination of Yttrium and Promethium A Precipitation Technique M. E. PRUITT,IR. R. RICKARD, and E. 1. WYATT Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
F A procedure is presented for separating yttrium from the lanthanum group of rare earth elements b y precipitating the latter as iodates. Yttrium remains in solution and is determined separately. In fission product mixtures that have cooled a year or longer, Pm'47 can be determined readily after the separation of the lanthanum group elements from yttrium. Other applications of the general technique are suggested.
R
radiochemicsl analyses are required in the control of the proccss for the large scale recovery of long livcd fission products. The feed materials for the rccovery process most often are the 11-aste solutions from processes for the rccovrry of irradiated reactor fuels. The solutions usually have becn cooled for several years to rid them of short lived radionuclides. Some of the radionuclides recovered are: SrgO,Csla7, Ce144, and Pml47. Of these PmI47 has been the most difficult to determine because of the presence of other rare earth radionuclides in old fission product mivtures and because PmI47 is a weak beta emitter with no associatrd gamma emission. The rare earth radionuclides present in mixed fission products vary with bombardment timc., cooling time, and APID
the history of the sample. Those likely to be found in fission product mixtures that have cooled for a year or more are listed in Table I. Since classic methods (18, 96) can be used to separate cerium from the trivalent rare earth elements, it becomes necessary only to separate promethium, praseodymium, samarium, and europium from yttrium. When this latter separation is accomplished, Pm147 can be determined rather easily in the remainder of the group n-ithout further separation because Pr144 will decay within 2 to 3 hours, Sm151 is too weak to interfere with GeigerAluller beta-counting techniques, and Eu155 will be present in negligible amounts. Ion exchange techniques for separating the rare earth elements from each other have been reported by Cuninghame (5j, Ketelle and Boyd (IW), Xervik (17), Petrow (80), and many others. However, ion exchange procedures for determining Pm147 are not easily adapted to the rapid analysis of a large number of samples. Extraction techniques for separating rare earth elements have been used by Kleinberg (16), Handley (9), Stevenson and Servik (WS), and others. Various precipitation techniques have also been described (1-3, 1 1 , 1 6 , 2 2 , 2 ~ ) . The development of a procedure for separating yttrium from the lanthanum
group elements by iodate precipitation of the latter is described herein. This procedure has been used a t the Oak Ridge Xational Laboratory for the past 3 years (21j . Although the radionuclides of yttrium are not valuable from a production standpoint Y9O and Ygl are nearly always present in fission product mixtures. The separation of these radionuclides from the lanthanum group elements is imperative if PmI47 or any of the shorter lived rare earth radionuclides are to be determined v i t h any degree of accuracy. Also, it is frequently desirable to determine Y90 and/or Ye1 in certain samples. Since promethium has no stable isotope that can be used as a carrier for PmI4', it is necessary to use a stable rare earth element that has chemical
Table I. Rare Earth Radionuclides Present in Aged Fission Products
Radionuclide Y" Y91
Ce14' Pr14( PmL47 Smlbl Eu166
Half Life 64.2 h 57.5 d
285 d
Fission Yield, yo (Daughter of SPOO) 5.4
6.0
17.27 m (Daughter of Ce14') 2.64 y 2.7 -93 y 0.45 1.7 y 0.03
VOL. 34, NO. 2, FEBRUARY 1962
283
properties very similar to those of promethiurn. Hopkins (10) gives the general order of increasing solubilities of the compounds of the rare earth elements to be as follows: La, Ce, Pr, Nd, P m , Sm, E u , Gd, Tb, Dy, Ho, Y , Er, Tm, Yb, and Lu. Since promethium falls between neodymium and samarium, it would appcar reasonahlc to use a mixture of ncodymium and samarium as a carrier for promethium if one wished to separate promethium from ytt,rium b y precipitation. T o ascertain the best conditions for the precipitation of the lanthanum group iodates, a study was mad? of the solubilit'ies of the iodates of neodymium and of yttrium as a function of the concentration of hydrogen ion and of iodate ion. Varions prccipitation t'echniques were st'udic,d in an effort to prevclnt occlusion of yttrium in the iodate precipitat,c. A rapid (30 minutes) radiochemical procedurc iTas developed for separat'ing promethium and t'he other lanthanide elemcxnts from yttrium b y precipitating t'heir iodates from homogeneous solution. L-sually 75% of the neodyniiumsamarium carrier is recovered, and less than 0.1% of the radioactire yttrium is retaincd The over-all time required for a I'm147 determination is about 11,'2hours. U y the use of yttrium carrier as well as the neodymium-samarium carrier, \-t'trium can be determined separately ifter the first iodate precipitation (separation of promethium from yttrium). However, the ratio of promethium to yttrium in some samples makes this practice impracticable. SPECIAL REAGENTS
hlised Carrier. Equal parts by weight of the osides of neodymium and samarium were dissolved in dilute HCl solution. The resulting solution was diluted to give a concentration of neodymium plus samarium equivalent to 20 mg. of their oxalates per milliliter when precipitated as such. The solut,ion was then standardized b y the oxalatr precipitation method. Wash Solution. A 42.8-gram yuantity of reagent grade KIOa was added to 1 liter of a standard solution of HNOI (0.SV). The solution was warmed to dissolve the KI03. Yttrium Carrier. Yttrium nitrate hexahydrate was dissolved in dilute HC1 solution. The resulting solution vias diluted to give a concentration of yttrium equivalent to 20 mg. of yttrium oxalate per milliliter. The solution was then standardized by the oxalate precipitation method. Aqueous Suspension of Talc. One gram of U.S.P. talc (powder) was suspended in 1 liter of distilled water. The suspension was mixed thoroughly before it was used. Ethylene Glycol. Reagent grade ethylene glycol was used without further purification. 284
ANALYTICAL CHEMISTRY
Periodic Acid. Reagent grade HI04 was used without further purification. Zirconium Holdback Carrier. About 10 grams of zirconyl chloride, ZrOCla, was added to 1 liter of distilled water. The mixture was heated to dissolve the ZrOC12. PROCEDURE
Promethium-147. Place in a 50-ml. glass centrifuge tube t h e test portion of t h e aqueous sample, 1 nil. of Sd-Sm carrier (and 1 nil. of Y carrier, if yttrium is t o be determined in t h e same test portion), 1 ml. of Ce holdback carrier, 8 ml. of concentrated "03, approximately 100 mg. of solid S a B r 0 3 , and 10 nil. of 0.35M HI08. Heat the tube to hasten oxidation of cerium. Stir the mixture and digest it in an ice bath for 2 to 3 minutes. Centrifuge the mixture and decant the supernatant liquid into a clean 50-nil. centrifuge tube. Discard the Ce(IOJ4 precipitate. T o the supernatant liquid, add 5 drops of Zr holdback carrier. Digest the mixture in a n ice bath for 2 to 3 minutes. Centrifuge and decant the supernatant liquid into a new 50-ml. glass centrifuge tube. Discard the precipitate Place the tube in a n ice bath and very cautiously add a n excess of carbonate-free 1911 NaOH (-10 inl.). Centrifuge the mixture and discard the supernatant liquid. Dissolve the precipitate in a minimum of 621 HCl; then add 0.1 ml. of talc suspension, and 2 ml. of ethylene glycol. Neutralize the solution with dilute h-H40H, dilute i t to 20 ml. with water, and add 1 ml. of concentrated "03. Cool the centrifuge tubc in an ice bath for 3 minutes; then add solid periodic acid (an amount equal to ten times the weight of Sd-Sm carrier) to give a good yield of mixed iodates. Centrifuge the mixture and discard the liquid (save the liquid if a n yttrium determination is desired). Add about 20 ml. of special wash solution; then heat the mixture almost to boiling or until most of the rare earth element iodates have dissolved. Cool the mixture in an ice bath with occasional stirring, centrifuge it, and decant the supernatant liquid. Repeat the wash step. Discard the supernatant liquid. Dissolve the precipitate in dilute HCl. Dilute the solution to -15 ml. with water and add ~ 1 ml. 0 of 12M NaOH to precipitate the rare earth element hydroxides. Wash the precipitate thoroughly with mater. Dissolve the precipitate with dilute HC1 and dilute the solution to 20 ml. with water. Heat the solution and add to i t about 20 ml. of a saturated solution of oxalic acid to precipitate the rare earth elements as oxalates. Wash the precipitate with hot water and filter the mixture through a Hirsch funnel. Weigh the precipitate and mount it for counting, Allow sufficient time for the decay of the 17-minute Prld4before counting the Pml47. Count the precipitate first without a n y absorber and again with a n absorber of sufficient thickness to absorb the Pm147 (about 50 mg. cm.-2) to ascertain whether any
contaminants were carried through the procedure. Radioyttrium. Introduce into a 50ml. glass centrifuge tube 1 ml. of t h e Y carrier, 1 ml. of the Zr holdback carrier, t h e test portion of t h e sample, and 0.1 ml. of talc suspension. Neutralize t h e contents of t h e tube t o litmus with dilute K H 4 0 H solution. -4dd 1 ml. of 6 X HS03. Introduce 2 ml. of ethylene glycol; then dilute the contents of the tube to 20 ml. with water. Cool the tube in an ice bath for a t least 3 minutes; then add crystals of periodic acid (about 1 gram) to give complete precipitation of the Y carrier and Zr holdback carrier. Centrifuge the mixture and discard the supernatant liquid. Dissolve the yttrium iodate out of the precipitate by adding 20 ml. of the special rrash solution and heating the mixture. Cool i t in an ice bath for a few minutes, centrifuge the mixture, and decant the supernatant liquid into a clean 50-ml. glass tube. Discard the precipitate, which contains the iodates of Zr and the rare earth metals. Add 5 ml. of 6.11 NaOH, centrifuge the mixture, and discard the supernatant liquid. Dissolve the precipitate in 6 V HC1; thcn add 10 ml. of water. Precipitate the Y as the hydroxide with concentrated 5H40H. Wash the precipitate with water. Dissolve the precipitate with a few drops of 6M HCl and dilute the resulting solution to 20 nil. with water. Warm the solution and add to i t 20 ml. of saturated oxalic acid solution. Wash the precipitate with hot water, filter the mixture, and mount the precipitate for beta counting. The final precipitate may contain both YgOand Ygl. If a measurement of only the Y91 is desired, they should be counted together and again after Y9O has decayed out. The difference in the initial and final count (corrected for decay of Y9l) is due to Y90. RESULTS
The studies indicated by the first three subheadings immediately below were made to establish the optimum conditions for separating promethium from other fission products. It was necessary that the separated precipitate be relatively free of radioyttrium and other radionuclides that might interfere with the counting of Pm147. Since the correct formulas of the compounds resulting from the precipitation of yttrium and neodymium in the iodate forms are not kno\Tn with certainty, it was decided to prepare these iodates under conditions that could be duplicated easily. Yttrium iodate was prepared by adding reagent grade potassium iodate to a neutral solution of yttrium nitrate that contained 1 me. of Y9l. The precipitate was washed with water, and the suspension was filtered through a sintered-glass funnel. The yttrium iodate \vas washed with ethyl alcohol and with ether and mas vacuum desiccated to constant lveight.
A. N o K I 0 3 B. 0 . 0 5 M KI03 C. O . I M KIOJ D. 0 . 2 M K I 0 3 E. 0 . 3 M K I D 3
LL
0
5 2 0
+ 5CO
4
L
l
z V
00 5 CONCENTRATION
02
04
07
10
OF NITRIC ACID, M
CONCENTRATION OF tvITRIC ACID, M
Figure 1, Solubility curves for yttrium iodate in nitric acidpotassium iodate solutions a t 2 5 " C.
Seodyniium iodate was prepared in a similar "a?; Sd147 was used as a tracc,r. The results of x-ray diffraction examination of t,he iodates of neodymium and of yttrium indicated that they a r t amorphous. The results of specific activity measurements, thermal decomposition studiw, and tracer studies indicat'e that the compounds were easily duplicated. These results also suggest t,hat t'he neodymium iodate is a mixture of Kd(OH) (IO3), xHzO and Xd(OH)zIO3..zH?O. Solubilities of Yttrium Iodate and Neodymium Iodate. Yttrium iodat'e a n d neodymium iodate t h a t ryere tagged viith T91 and Sd147, respectively, n-erc used to obtain the solubility data shown in Figurw 1 and 2. The solubilit'y data of yttrium iodate (Figure 1) were obt'ained by adding the tagged yttrium iodxte to solutions of various nitric acid and iodate ion concentrations. The solutions were allowed to remain in contact viith an excess of t h p iodate pwcipitate until a change in solubility \vas no longer ohserved. This equilibrium condition was determined by counting aliquot's of the supernatant liquid over a period of several \veeks. h n aliquot of the solution in contact Iyith the tagged yttrium iodate was evaporatcd on a watch glass and u-as counted on an end-lvindow Geigrrl\luller countcr. From the previously determined sperific activity of the yttrium iodate, tho counting rate of the supernatant liquid was a direct measureinent of t'he solubility of yt't'rium iodate in each solution. The solubility of neodymium iodate (Figure 2) was determined by the same procedure, except for counting. The Sd"' was counted by a well-type gamma scintillation counter. The data of Figures 1 and 2 shorn that the optimum iodate and nitric acid concentrations for precipitating neodymium as the iodate and at the same time leaving yttrium in solution are 0.2-11 and 0.811, respectively. Under these conditions, yttrium iodate and neodymium ,
Figure 2. Solubility curves for neodymium iodate in nitric acid-potassium iodate solutions a t 25" C.
iodate are soluble to the eytent of 1.3 and 0.25 mg. per ml., respectively. Optimum Conditions for Precipitating Neodymium Iodate in the Presence of Yttrium Iodate. Several methods of precipitating neodymium in t h e iodate form were tried. T o study t h e degree of separation of yttrium and neodymium in each method, yttrium a n d neodymium were tagged with Y9l and Prnl47, respectively. The weak beta radiation from Pm147, in sharp contrast with the strong beta radiation associated with Y g l facilitates , differentiation betn-een these two radionuclideb and, therefore, determination of the degree of separation of yttrium and neodymium. The results of all the methods t h a t were studied for precipitating neodymium iodate in the presence of yttrium iodate are shown graphically in Figure 3 . The data were obtained b y counting the dried neodymium iodate precipitate through successively thicker aluminum foils b y a Geiger-llfuller counter.
b
i
. \
L
1
L l 'O,-----------d
. .. 8 . SEPARATION SI RAP13 h D D I T 8 X C F R E b i E t v T S C. SEPARATON BY HOMOSENEOdS :REClPi7AT10h 0 . SEPARAT,ON BY HOM3GEYEOLS PeECIP'TATIOk A h C INDUCED U d t L E A T l O U
io
I
1
40 60 80 IX 420 THICKNESS O ' S L ~ P ~YdPJ A 3 i 3 R g E F vg I m ~
'43
Figure 3. Promethium-1 47-yttrium-91 absorption data
Curve A, Figure 3, is the reference curve for the mixture of Pm*47 and Y9l before any separation m s made. The results of the precipitation of neodymium iodate by rapid addition of reagents are shonn in curve B, Figure 3 . They indicate that about 15yo of the Ygl is coprecipitatetl with the neodymium. A conductometric titration of ncodymium nitrate with potassium iodate showed that neodymium iodate did not precipitate whrn the solution became saturated with neodymium iodate. It was at first believed that the coprccipitation of yttrium might be avoided by a homogeneous precipitation of neodymium iodate. This \vas accomplished by the reaction of ppriodic acid and ethylene glycol in solution t o control the rate of crystal growth. The rtsults, shown as curvp C, Figure 3, were poor. The data of curves B and C indicate that coprecipitation is responsible for the poor separations. Ostwald (19) and von Weimarn (26) were instrumental in developing the classical theory of physical mechanisms for precipitation processes. From their work, it can be concluded that the rate of precipitation and the number of particles are proportional to the degree of supersaturation a t the time of precipitation. Duke and Brown (6) and Buckley (4) suggest also t h a t in any physical mechanism of precipitation the growth process must be considered. Fischer (7) has recently suggested a mechanism of nucleation that retains many of the features of other concepts but extends the theory to deal with practical applications. On the basis of these concepts, i t was reasoned that if a crystal should grow from a solution supersaturated with respect t o both yttrium iodate and neodymium iodate, then the yttrium iodate would be occluded in the crystal of neodymium iodate. If the rate of formation of iodate ion is controlled in such a manner that i t becomes the rate-controlling step, then the solution should not become VOL. 34, NO. 2, FEBRUARY 1962
285
saturated with respect t o yttrium iodate prior t o precipitation of neodymium iodate. If a sufficient number of nucleation sites were available, the precipitation would start a t the time the solution became saturated with respect to ncodymium iodate. n'ucleation processes in analytical chemistry have been studied by Klein and Gordon (13) and by Klein, Gordon, and K a l n u t ( 14, 15). Also, the addition of various foreign particles to provide nucleation sites has been reported (8). Talc (MgSiOs) was added to the solution to offer nucleation sites for neodymium iodate formed by the method of homogeneous precipitation. The results of a honiogrnrous Precipitation in the presence of 0.1 nig. of finely divided talc are shoirn as curve D of Figure 3. They indicate that only about 570 of the original yttrium remains u-ith the neodymium precipitate even without any washing of the precipitate. It could be argued that solid neodymium iodate would offer sites more receptive to the freshly przcipitating neodymium iodate than would talc. However, talc has the advantages over neodymium that the time of its addition does not have to coincide with the time a t which the solution becomes saturated, additional talc does not have to be added when neodymium iodate is rcprecipitated, and less yttrium is occluded in the crystal. By the radiochemical procedure described for PmI47, more than 99.970 of the yttrium presrnt is separated from the rare earth elements. Since about 75y0 of the neodymium-samarium carrier is recovercd, the precipitation can be rcprated if necessary to obtain the desired purity of Pm147. The retention of the small amount of yttrium is probably due t o a micro portion of the solution becoming temporarily saturated with yttrium iodate or to the rapid rate of crystal growth. If these should be the causes, then separation could be improved by using vigorous agitation to provide a more nearly homogeneous concentration of nucleation sites and /or by decreasing the rate of formation of the iodate ion. S o difference was observed in the degree of separation whether yttrium was present in trace or milligram quantities. In Table I1 is shown the degree of separation of yttrium when the precipitate is recrystallized from a solution 0.8.V in nitric acid and 0.2M in potassium iodate. The talc carries through the procedure and is available to offer nucleation sites in each recrystallization. I n this procedurp, the talc is weighed along with the final precipitate, but the resulting error is negligible in comparison with the error3 of counting. The talc can be removed by filtration before the oxalate precipitation step if it seems desirable. A study was also made to determine 286
ANALYTICAL CHEMISTRY
how much E d carrier would follow yttrium in the recommended radioyttrium procedure. Srodyniium-147 was used as a tracer, and less than 0.5% of the neodymium originally present n-as carried into the final precipitate of yttrium oxalate. Carrying of Promethium-147 by Neodymium-Samarium Carrier. -4 solution of mixed neodymium-samarium carrier was spiked with Pm147. A precipitation was carried out as outlined in the procedure. The final precipitate was dissolved, and the resulting solution was diluted sufficiently t o decrease the concentration of solids t o a negligible amount. .4n aliquot of this solution was evaporated to dryness; a corresponding aliquot of the tracer solution nas counted a t the same time. Promethium is carried quantitatively by the neodymiumsamarium solution under the conditions given. Since the beta radiation from Pmlr7 has a maximum energy of 0.27 m.e.v., much of the radiation will be absorbed in the final precipitate. If an endv\.indom Geiger-Muller counter is used, another large part of the beta activity will be absorbed by the window, air gap, and the material used t o cover the precipitate. Although it is possible to correct for these losses, the best results are obtained by starting u i t h a test portion that contains about 106 c.p.m. of Pm147, dissolving the final precipitate, and diluting the resulting solution sufficiently that an aliquot of it taken for counting has a negligible amount of solids. The counting efficiency m u d be ascertained for the instrument used, and suitable corrections must be made for the arrangement of the sample. The results obtained in drtermining Pm147 by the recommended procedure do not differ significantly from those obtained by 4-71. counting of Pm147. This agreement is alio trur for Ygl results. DISCUSSION
Thc degree of decontamination required varies rrith the initial concentrations of undesired radionuclides. These variables may necessitate the use of additional decontamination steps depending on the particular activity sought. For euample, one may desire to precipitate the rare earth elements with hydrofluoric acid first if other activities are present in far grrnter quantities than are those of the rare earth elements. The authors have used many variations of the basic separation of neodymium and yttrium, sometimes ridding the sample of cerium bcfore the neodymium and yttrium are separated, a t other timcs isolating the yttrium first. Cerium has been removed by extraction u-ith di-Zethyl-
Table 11. Effect of Recrystallization of Neodymium Iodate on Its Retention of Yttrium after Homogeneous Precipitation'
Test Portion 1 2 3 4 5 6
Tttrium Retained, yo One Two recrystal- recrystal- recrystallization lization lizations ?io
3.99 5.75 5.28 5 35 5.56 4.53
0.7 0.8 0.9 0 8 0 5 0 4
0.04 0.02 0.03 0.05 0 04 0 03
Recrystallization does not seriously affect amount of neodymium precipitate recovered. Even after two recrystallizations, yield is still greater than 607,.
hexyl phosphoric acid prior to the separation of neodymium and yttrium. The procedures for radioyttrium and PmI47 have been adapted for the determination of other rare earth elements. Seodymium-147 and La1a have been determined in fresh fission product solutions by the use of the procedure for promethium with the aid of appropriate carriers. The two are precipitated together, and each is determined by gamma scintillation spectrometry if the contribution that La140makes to the 0.09- and 0.54-m.e.v. photopeaks associated ITith NdI4" is taken into account. K i t h the aid of europium carrier instead of neodymiumsamarium carrier, Eu'55 has been separated by the promethium procedure. The Eu'j5 is determined by gamma counting to eliminate any interference from Pm147. Cerium-144 has been determined in fission-product mixtures more than one year old by use of a cerium-praseodymium carrier instead of the neodymium-samarium carrier and counting the beta activity of the precipitate by use of an absorber of sufficient thickness to absorb the radiation from Pn1'47 and from Ce'44 (the Prla4daughter of Ce144 will be in secular equilibrium with an equivalent to the Ce"4 and has sufficient energy to penetrate the absorber). LITERATURE CITED
(1) Ballou, N. E., "Radioche,yical Studies. The Fission Products, Book 111,
C. D. Coryell, K. Sugarman, eds., Paper 292, hicGra\v-Hill, New York,
1951. (2) Ballou, N. E., Ibid., Paper 296. (3) Boldridge, W.F., Hume, D. K., Ibid., Paper 294. (4) Buckley, H. E., "Crystal Growth," Wiley, New York, 1951. ( 5 ) Cuninghame, J. G., J . Inorg. & Xuclear Chem. I, 163 (1955). (6) Duke, F. R., Brown, L. hl., J . A m . Chem. Soc. 76, 1443 (1954). ( 7 ) Fischer, R. B., Anal. Chin. Acta 22, kOl (1960).
(8) Fischer, R. B., Rhinehammer, T. B., ANAL.CHEW26, 244 (1954). (9) Handley, T. H., private communication
to R. R. Rickard, 1958. (10) Hopkins, B. S., “Chapters in the Chemiapy of the Less Familiar Elements, Vol. 1, Chap. 6, p. 12, Stipes Publishing Co., Champaign, Ill., 1939. (11) Jaquith, R. H., Michigan State Univ. Microfilms (Ann Arbor, Mich.) L. C. Card No. Mic 58-5713, 72 pp., Dissertation Abstr. 19, 1554 (1959). (12) Ketelle, B. H., Boyd, G. E., J . Am. Chem. SOC.73, 1862 (1951). (13) Klein, D. H., Gordon, L., Talanta 1. 3.14 - - f1958). ~ - I
\ - - - - ,
(14) Klein, D. H., Gordon, L., Walnut, T. H., Ibid., 3, 177 (1959). (15) Ibid., 187.
(16) Kleinberg, J., “Collected Radiochemical Procedures,” Los Alamos Scientific Lab. Rept. No. LA-1721 (2nd ed.) (1958). 17) Kervik, W. E., J . Phys. Chem. 59, 690 (1955). 18) Noyes, A. A., Bray, W.C., “A System of Qualitative Analysis for the Rare Elements,” hlacmillan, New York, 1927. 19) Ostwald, K., 2. physik. Chem. 22, 289 (1897). (20) Petrow, H. G., AXAL. CHEM. 26, 1514 (1954). (21) Rickard, R. R., Wyatt, E. I., “Promethium and/or Yttrium Activity in daueous or Organic Solutions.” Method
Master Analytical Manual, TID-7015, Suppl. 3. (22) Shaver, K. J., ANAL.CHEM.28, 2015
(1956). (23) Stevenson, P. C., Nervik, W. E.,
Natl. Acad. Sci.-Natl. Research Council NAS-NS 3020 (1961). (24) S h e , C. R., Gordon, L., ANAL. CHEM.25, 1519 (1953). (25) Vickery, R. C., “Chemistry of the
Lanthanons,” Academic Press, New York, 1953. (26) von Weimarn, P. P., Chem. Revs. 2, 217 (1925).
RECEIVEDfor review August 14, 1961. Accepted December 11, 1961. Southeast-Southwest Meeting ACS, New Orleans, La., Fall of 1961.
Far-Ultraviolet Spectroscopic Detection of Gas Chromatograph Effluent WILBUR KAYE Beckman Instruments, Inc., 2500 Harbor Boulevard, Fullerton, Calif.
b A Beckman far-ultraviolet DK-2 spectrophotometer has been adapted to record the spectra of effluent from a Beckman GC-2 gas chromatograph. Heated flow-through cells of 1.0-, 5.0-, and 10.0-cm. optical path length have been used, and the effects of wavelength and cell hold-up have been evaluated. The absorptivities of almost all organic vapors are sufficiently high to permit their quantitative detection from the chromatograph and, in favorable cases, to allow their identification. M a n y materials possess such high absorptivity to allow the far-ultraviolet detector to exceed the sensitivity of the thermal conductivity detector and even rival the hydrogen flame detector. The optical absorption of effluent may b e obtained as a function of elution time or wavelength. Rapid repetitive wavelength scans are possible.
T
HE FAR-ULTRAVIOLET SpeCtrOphotometer and the gas chromatograph complement each other (6). The former allows the selective and sensitive detection of gases, while the latter provides a convenient purification of sample. The near-ultraviolet spectra of organic compounds are seldom as characteristic as infrared spectra; however, as shorter wavelengths are employed, greater utility is found. At a wavelength of 1700 A,, almost all organic compounds have high absorptivities which may be 1000-fold greater than maximum absorptivities in the infrared region.
Earlier investigations of the farultraviolet region revealed that it had greatest appeal for the study of gases (8). Because of the extreme broadening of absorption bands of condensed phases, the study of liquids and solids in this region is restricted. However, many low molecular weight organic and inorganic gases possess discrete and characteristic far-ultraviolet spectra. The samples emerging from a gas chromatograph are in an ideal condition for study by an ultraviolet spectrophotometer. The handling of hot gases is not difficult, and the isolation of sample components greatly facilitates the study of the spectra of impure samples. Fractions need not be delicately transferred or condensed and may be recovered undamaged from the cell exhaust. Comparison with Other Detectors. Detectors based on far-ultraviolet absorption, infrared absorption, nuclear magnetic resonance. a n d mass spectrometry are selective in t h a t their response t o different compounds may vary considerably. The far-ultraviolet and mass detectors are more sensitive than the other selective detectors and, for this reason, can be coupled directly to the output of the column. The response time of the far-ultraviolet detector can be very fast although timeof-flight mass spectrometers may scan faster. The far-ultraviolet detector can possess a higher quantitative accuracy than other methods, provided absorptivity values on pure compounds can be obtained. Far-ultraviolet spect r a can be partially predicted, although
group frequencies are not as characteristic as infrared spectra. Near-ultraviolet spectra have been used in the identification of fractions isolated by chromatography (8). Radiation a t 2536 A. has been used to monitor polynuclear aromatic compounds in the gas phase from a chromatograph ( 3 ) . Usually the near-ultraviolet absorptivities are lower, and the bands are broader than in far-ultraviolet spectra. INSTRUMENTATION
Figure 1 shows a block diagram of the equipment used. Two gas chromatographs] a Beckman GC-2 and a Beckman ThermotraC, were employed. The unbalance of the thermal conductivity bridge was recorded with a n adjustable recorder of 1-mv. full scale maximum sensitivity. The temperature of the detector block was always maintained equal to or above the temperature of the column. A current of 325 ma. was passed through the filaments of the thermal conductivity bridge. Samples emerging from this detector were conveyed to an absorption cell in the spectrophotometer through a heated ‘/*-inch copper tube. One section of this tube was maintained a t a known temperature which was colder than any other part of the equipment in contact with the sample. A bypass valve between the cold trap and the absorption cell permitted static isolation of any emerging fraction in the cell. A DK-2 monochromator modified for far-ultraviolet performance was used (5, 7). This instrument was purged with dry nitrogen. I n most cases, no compensator was placed in the reference path. The monochromator was equipped with a time drive accessory to VOL. 34, NO. 2, FEBRUARY 1962
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