ml. of hydrofluoric acid were added to the solution. The hafnium was precipitated as barium fluorohafniate b y the addition of 1 ml. of a solution containing 50 mg. of barium ion. The precipitate was washed several times with water t o eliminate the excess barium, then filtered through a tared molecular membrane filter ( 7 ) . The filter was dried, weighed, and mounted for counting. The vial containing the standard solution was crushed in a beaker, and 1 ml. of the carrier solution and 1 ml. of concentrated nitric acid were added, The solution was transferred to a Lusteroid tube and 2 ml. of concentrated hydrofluoric acid was added. Then the hafnium was precipitated by the addition of 50 mg. of barium ion in solution. The precipitate was washed t o remove excess barium and filtered through a tared molecular membrane filter. The fiIter was dried, weighed, and mounted for counting. A single-channel y-ray scintillation spectrometer mas used for counting. The geometry of the counting arrangement mas similar for standard and sample. The 89-k.e.v. peak of hafnium-175 and the 133- and 480-k.e.v. peaks of hafnium-181 were prominent in the scans obtained ( 3 ) . A small peak a t 750 k.e.v. due to residual niobium and zirconium \vas also apparent. T o find the weight of the hafnium in the sample, the ratio of the intensity of any one of these hafnium peaks in the sample scan to the intensity of the same peak in the standard scan was determined. This ratio was then corrected for the relative carrier yield of the sample and the standard. The corrected ratio was multiplied by the weight of the hafnium in the standard. I n seven determinations on a typical zirconium alloy sample this method
gave an average hafnium content of 77 p.p.m., with a standard deviation
of 9.
Discussion. T h e result for this method agrees reasonably well with t h e value of 69 p.p.m. (sample A, Table I) obtained for t h e same sample by t h e hafnium-175 method. T h e total time required for this procedure was about 20 hours, of which 14 hours was required for t h e ion exchange separation. Although use of these long-lived activities requires time-consuming separation before counting, rapid handling of the sample after irradiation is not required. A laboratory furnished with suitable counting equipment can arrange service irradiations in a nuclear reactor and suffer no appreciable loss of the activities during shipment. About 30% of the hafnium carrier was usually recovered from the separation process. The remainder either is not adsorbed by the resin or is discarded in the fractions which contained zirconium activities. The sensitivity of the method depends only on the amount of hafnium activities required for counting; because of the separation achieved chemically and by y-ray spectrometry, no other elements interfere. If necessary, one third of the activity produced under the conditions of this experiment could be counted. The irradiations were of 8 days’ duration, which is only a small fraction of the time required to produce the maximum amount of activity from the hafnium present. Therefore, by utilizing a smaller amount of activity and by irradiating for much longer
times, the sensitivity could be extended t o a small fraction of the 77 p.p.m. found in these experiments. Probably 10 p.p.m. is a reasonable estimation. LITERATURE CITED
(1) Aten, A. H. W., Jr., Xed. Tijdschr. Natuurk. 10, 257 (1943). (2) Birks, L. S., Brooks, E. J., ANAL
CHEM.22, 1017 (1950). (3) Burson, S. B., Blair, K. W., Keller, H. B., Wexler, S., Phys. Rev. 83, 62 (1951). (4) Heydenburg, K. P., Temmer, G. M., Ibid., 98, 1198 (1955). (5) Hudgens, J. E., Jr., Dabagian, H. J., Nucleonzcs 10, No. 5, 25 (1952). (6) Jenkins, E. N., Smales, -4. A., Quart. Reus. (London) 10, 83-107 (1956). (7) Jervis, R. E., “Improved Filtration System for Assay of Radioactive Precipitates,” Publ. 428, Atomic Energy of Canada, Ltd., Chalk River, 1957. (8) LBveque, P., Proc. Intern. Conf. Peaceful Uses Atonzac Energy, Gensva, 1966 15, 78 (1956). (9) LEvique, P., Goenvec, H., Bull. soc. chzm. France 1955, 1213. (10) illortimore, D. SI., Soble, L. A., ANAL. CHEM.25, 296 (1953). (11) Smales, h..k., “Radioisotopes Techniques,” 1.01. 11, pp. 162-71, H. M. Stationery Office, London (1952). (12) Street, K., Jr., Seaborg, G. T., J. Ana. Chem. SOC.70, 4268 (1948). (13) TaJ-lor, T. I., Havens, W. W., “Physical Methods in Chemical Analysis,” Vol. 111, Walter Berl, ed., Academic Press, Sew York, 1956. RECEIVED for review September 26, 1957. Accepted February 3, 1958. Presented in part, Division of Analytical Chemistry] 133rd Meeting, .-ICs, San Francisco, Calif., April 1958.
Io n Excha nge-S pect rophotomet ric Determination of Thorium OSCAR A. NIETZEL, BERNARD W. WESSLING,’ and MICHAEL A. DeSESA Raw Materials Development Laboratory, National Lead Co., Inc., Winchester, Mass.
b Two ion exchange procedures were developed for the separation of thorium prior to spectrophotometric determination with thorin reagent. In the anion exchange procedure, possible cation interferences are removed by adsorption of their chloro complexes from OM hydrochloric acid onto Dowex1 resin. The more specific cation exchange method consists of adsorption of cations from the sample onto Amberlite IR-120 resin, elution of most of the cations with 2M hydrochloric acid, and recovery of the thorium by elution with 3M sulfuric acid. 1 182
a
ANALYTICAL CHEMISTRY
S
b y Banks and Byrd (2)of their comprehensive review of the analytical chemistry of thorium, the spectrophotometric determination of thorium with the disodium salt of 2- (2-hydroxy-3, B-disulfo-l-naphthy1azo)-benzenearsonic acid (thorin) has been widely adopted (4, 7 , 13). Menis et al. (10) recently reviewed other published applications of the thorin method and also cited several other chromogenic reagents which have been used or proposed for the photometric determination of thorium. While these latter reagents may be more INCE THE PUBLICATION
sensitive, they are all less specific than thorin. Ion exchange separations have been reported (1, 3, 6, 11) in which the thorium was selectively eluted from cation exchange resins or in which thorium was complexed with (ethy1enedinitrilo)tetraacetic acid (6) so that it was not adsorbed by the resin. As thorium is not adsorbed by strong-base anion exchange resin from hydrochloric acid, it may be separated from the many ions which are retained (8, 10). l Present address, Kuclear Products Division, Metals and Controls Corp., iittleboro, Mass.
I n this paper the experimental work leading to two ion excliange-spectrophotometric methods for the determination of thoriurn is described. APPARATUS AND REAGENTS
Beckman Model DU spectrophotonieter and 1-cni. Cores cells. Buret, 50-ml. capacity, approsimately 1 em. in diameter to be used for a n ion exchange column. A f l o ~rate of approsiiiiately 1 ml. per minute was used in all tests. Thorium nitrate stock solution, approximately 2 Ing. per ml. Dissolve 5.0 grams of thorium nitrate tetrahydrate in 1 liter of deionized water. Standardize by the oxalate precipitation method. Prepare less concentrated solutions by appropriate dilution of the standard bliorium nitrate. Thorin, 0.27,. Dissolve 2 grams of the reagent (obtained as Thoron from Fine Organics, Inc., 211 East 19t’h St., Keiv York) in deionized water and dilute to 1 liter. Prepare a n e x calibration curve for each fresh solution of the thorin reagent (2). Aniberlite IR-120, 20 to 50 mesh, sodium-form cation exchange resin. Convert the resin to the hydrogen form by repeated washes with 4.M hydrochloric acid. Ilorrex-1 chloride-form anion esclimge rwin, 50 to 100 niePh, with divinylbenzene. (Al! resin volumes e iiieasured as wet-settled in water.) SPECTROPHOTOMETRIC METHOD
The spectrophotometric procedure of Thomason (14) for tlie determination of thorium with thorin reagent was briefly reviewed. Khile the wave length of niaxinium ahsorbance has been indicated as 545 mb, the spectrum of the complex displayed an absorbance peak between 546 and 548 mp on tlie spectrophotometer used in this laboratory. At a wave length of 547 my, the system obeyed the Beer-Lambert lam in tlie range of 0.2 t o 2.0 mg. of thorium per 100 ml. The color m-as stable for at least 24 hours. Thomason recommended that any iron in tlie sample aliquot be reduced by boiling the solution n-ith hydroxylamine hydrochloride prior t o color development. However, it n-as found t h a t the addition of 2 ml. of 10% K./v.) I-ascorbic acid solution before addition of the thorin reagent reduced iron immediately at room temperature. K h e n solutions containing 5, 10, and 20 mg. of iron(II1) were treated according to the standard spectrophotometric procedure, the resultant absorbance was equiva!ent to 0, 3.5, and 4.2 y of thorium, respectively. Thus, even for a sample a t the loner end of the calibration curve (0.2 mg. of thorium), 20 mg. of iron n-ould cause lrss than 37, error. Solutions containing 2 and 5 mg. of uranium(T’1) gave absorbances equivalent to 2.8 and 8.4 y of thorium, so that 5 mg. of uraniumIVI’I would cause less than 501, error. The following procedure was used .
I
throughout this study for the spectrophotometric determination of thorium with thorin. After the thorium has been separated, evaporate the thorium-bearing solution to dryness in a beaker. Rinse d o m the sides of the beaker with 5 ml. of 551 hydrochloric acid added from a pipet. Warm to dissolre the thorium salt, nash donn tlie sides of the beaker, and dilute to about 20 nil. vitli deionized water. Add 2 ml. of 10% (.-./v.) ascorlic acid and mi.: well. Add 10 ml. of tliorin reagent by pipet, transfer the solution quantitatively to a 100-ml. volumetric flask, dilute to volume n ith deionized water, and mi.: well. hleasure the absorbance of the solution a t 5-47 mp against a reagent blank. ANION EXCHANGE SEPARATION
The least complex samples in which thorium was to be determined u-ere mixtures of thorium, iron, and uranium in 1Jf sulfuric acid. Kraus and Nelson have reported ( 9 ) the distribution coefficients of many elements betneen hydrochloric acid solutions and Dowex-1 anion exchange resin. Thorium is not adsorbed, while elements such as iron and uranium are.
,4n aliquot of a thorium nitrate solution containing 2.42 mg. of thorium was evaporated to dryneqs and the resultant salt n a s dissolved in 10 ml. of 9 X hydrochloric acid. This solution was transferred to a colunin containing 15 ml. of Dorvex-1 resin in 9 M hydrochloric acid. T h e column wa3 vashed with 9M hydrochloric acid and the effluent collected in 15-m1. portions. ilnalyees of these effluents revealed that four column volumes (60 ml.) of 9M hydrochloric acid wash solution yielded quantitative recovery of the thorium. TTlen mixtures of thorium, iron, and uranium were treated in a similar manner, as little as 0.1 mg. of thorium could be quantitatively separated from 20 mg. of uranium(T’1) or 40 mg. of iron(III), or 20 mg. each of iron and uranium. According to the work of Kraus and Nelson (9) the following elements, n hich have been reported to interfere in tlie thorin method, should be separated b y this technique: cerium (IT’), chromiuni(VI), hafnium, iron(III), uranium(1V) and (VI), and zirconium. However, yttrium, lanthanum, cerium(III), the rare earths, and titanium would not be removed, so that these elements would interfere if the tolerable limit was exceeded. Procedure. T h e following procedure is recommended for samples containing only cations adsorbed by Don ex-1 from 9 N hydrochloric acid. Transfer a n aliquot of the sample containing 0.3 t o 1.5 mg. of thorium t o a beaker of suitable size a n d evaporate t o dryness. Add approximately 25 ml. of 9iM hydrochloric acid and
Table
1. Test of Anion ExchangeSpectrophotometric Method
Thorium, RIg. Sample Yo. Added Found Recovered KPQ2527 KPQ 2529 HGP460
HGP461
X011e 0 196 Xone 0 I96 Sone 0 196
Sone 0 196
0 215 0 409 0 485 0 635 1.13 1.39 1.10 1.29
0 194
0 197
0.20
0 19
n a r m t o dissolve t h e salts. Allow the solution to cool, and paw over a column of 15 ml. of Dowe.;-1 resin in 9 X hydrochloric acid. Vash out the beaker with several small portions of 911.1 liydrochloric acid. Pass these ~ ‘ashings r orer the column and n ash the rcsin column viith GO nil. of 9J1 hydrochloric acid. Collect the effluent in a 250-m!. beaker. Evaporate the hydrochloric acid solutinn to dryness, add 10 nil. of nitric acid and 1 or 2 ml. of perchloric acid, and evaporate to dryness. Determine the thorium by tlie spectropliotornetric procedure previously described. (Milvation data obtained 11y treating aliouots of a standard thorium nitrate sohtion by the a1)ove procedure gave a n average absorbance of 0.692 for 1 mg. of thorium in the original aliquot. Results. Several samples which were known to contain thorium were spiked Tyith 0.196 ma. of thorium. T h e analyses obtained before a n d after spiking (Table I ) indicate a good recovery of thorium. CATION EXCHANGE SEPARATION
The anion exchange separation technique may not he used for the analysis of sulfuric acid leach liquors with thorin reagent, as no separation is obtained from elements such as the alkali metals, the alkaline earths, and the rare earths (9). I n addition to the positive error introduced b y some of these ions, their presence in the effluent also introduces a n indirect interference because they are present as the sulfate salts in sufficient quantities to prevent the full development of the thoriumthorin color. Attempts to eliminate this interference b y separating the thorium from the sulfate salts by solvent extraction with mesityl oxide, as described by Banks and Byrd (@, were unsuccessful. The failure of the mesityl oxide extraction in this application was due to tn-o factors. A yellowbrown color, due to oxidation products of the mesityl oxide, was imparted to the aqueous solution used to strip the thorium from the mesityl oxide. The presence of oxidation products in the strip solution was not a serious interVOL. 30, NO. 7,JULY 1958
* 1183
Table II.
Ileain
IR-100 IR-105 IIt-120
1.7 2 7 4 2
ference in the method of Banks and Byrd, because only a portion of the strip solution was used for color development. I n the present application the thorium content of the leach liquors is such that the entire strip solution must be taken for color development. Therefore, the oxidation products had to be destroyed by fuming with nitric and perchloric acids. I n addition to this difficulty, the presence of greater than 250 mg. of sulfate in the aqueous phase of the mesityl oxide extraction system resulted in an incomplete extraction of the thorium. In the sulfuric acid leach liquors which were to be analyzed, the sulfate-to-thorium ratio was so high that the tolerable limit of sulfate for quantitative extraction was exceeded. As the anion exchange separation technique is not applicable for sulfuric acid leach liquors, the possibility of applying a cation exchange separation technique was investigated. A cation exchange resin was desired which m u l d adsorb thorium quantitatively from sulfuric acid solutions and retain it while allowing selective elution of the interfering cations. Three sulfonic resins, Aniberlite IR-100, IR-105, and IR-120 were tested to determine thcir possible application. Solutions containing 2 mg. of thorium as thoriuin nitrate in 25 ml. of water, 03.11, and 1.0M sulfuric acid were added to columns containing 15 ml. of the hydrogen form of each resin. The columns Lvere washed with water and the efluent was analyzed for thorium. The amount of thorium retained by the resin was calculated from these data. 4 comparison of the adsorption characteristics of these three resins is presented in Table 11. Because of the superior adsorption characteristics of IR-120, this resin was chosen for further n ork. Citrate (3, 11), hydrochloric acid ( 5 ) , and sulfuric acid ( 1 ) have been used to elute various cation exchange resins for the removal of cations adsorbed along with thorium. Hydrochloric acid was chosen for this application. Several columns containing 15 ml. of Amberlite IR-120 resin and 2 mg. of adsorbed thorium were prepared. The columns were eluted with 150 ml. of hydrochloric acid a t various concentrations. The results of this study are shown in Figure 1. The evident 1 184
nig. of absorbed thorium were eluted with 300 ml. of sulfuric acid a t various concentrations. The sulfuric acid in the eluate was removed by evaporating the solution to dryness, and the resulting salts were analyzed spectrophotometrically by the thorin procedure. The results of this study, also presented in Figure 1, show that 35f sulfuric acid is the optimum concentration for nearly quant'itative elution of thorium from IR-120 cation eschange resin.
Effect of Resin Capacity on Adsorption of Thorium 5,.Idsorption from Capacity, Neq. per Gram Kater o , ~ J {H,SO~ 1 , O J H,SO~ ~
ANALYTICAL CHEMISTRY
--
100 100 100
26 42
I 1
97
100
100
1 0
2
Molarity o f
4
6
8
Eluent
Figure 1 . Elution of thorium from IR120 cation exchange resin with hydrochloric acid and sulfuric acid
choice for the elution of interfering cations is 2M hydrochloric acid. Sulfuric acid ( I I ) , 1.25JI sodium bisulfate ( I ) , 0.5-11 oxalic acid ( 5 ) , and citrate a t p H 4.0 (3) have been used to recover thorium from cation exchange resins. Sodium bisulfate was obviously not suitable for this work. Oxalate is a serious interference in the development of the thorium-thorin color, and must be destroyed before color development. However, it x i s found that 150 nil. of 0.5M oxalic acid could be destroyed by evaporating the solution to dryness with nitric acid if 1 drop of saturated potassium permanganate was added to serve as a source of manganous ion to catalyze the decomposition. When 0.5N oxalic acid \yas used as eluent, up to 0.3 mg. of thorium v-as eluted quantitatively from 15 ml. of IR-120 resin. Larger amounts of thorium were not completely eluted even by doubling the volume of the eluent. Failure to obtain quantitative elution was probably due to the fact that IR-120 has a higher capacity than the resin used by Dyrssen (6) in his work with oxalic acid. As a study of the possible application of eluting with other complexing agents would require an initial investigation to determine their effect on the color development bet ween thorium and thorin, sulfuric acid was tested as an eluent. A series of columns containing 15 ml. of IR-120 resin and 2
Procedure. Pass a n aliquot of the sample, which contains 0.3 t o 1.5 mg. of thorium in no more than 25 ml. of 1-If sulfuric acid, over 15 nil. of wet-settled IR-120 resin in t h e hydrogen form. Wash the resin with 150 nil. of 2 M hydrochloric acid. Elute t h e thorium with 300 rnl. of 3M sulfuric acid. Collect the eluate in a 600-mi. beaker. Evaporate the eluate to dryness, add 10 ml. of nitric acid and 1 to 2 ml. of perchloric acid, and evaporate to dryness again to destroy any organic matter from the resin. Rinse down the sides of the beaker with 5 nil. of 5M hydrochloric acid and warm to dissolve the thorium salt. Kash down t'he sides of the beaker and dilute to 20 ml. with deionized water. Develop and measure the color as described before. Calibration Data. Aliquots of a standard thorium solution containing fioni 0.196 t o 1.96 mg. of thorium n-ere added to columns containing 1 nil. of IR-120 resin. T h e columns were washed with 150 ml. of 2 M hydrochloric acid and eluted with 300 ml. of 3 M sulfuric acid. The sulfuric acid eluates were evaporated to dryness and the thorium was determined by the thorin procedure. For the eight aliquots taken, the range in absorptivity was 0.673 to 0.699, the average was 0.681, and the coefficient of variation was 1.3%. The absorbance index is in such units that an aliquot containing 1 mg. of thorium treated according to the recommended procedure yields a solution with an absorbance of 0.681 a t 547 mw. Interferences. I n general, the affinity with which cations are held by a cation exchange resin increases with the charge of the cation (1%'). Therefore, a clean separation of thorium from mono- and divalent cations and a partial separation from trivalent cations should be achieved upon eluting a cation exchange resin with 2-11 hydrochloric acid. This expected behavior was confirmed in a study made to determine the effectiveness of separating thorium from the common elements which could be present in uraniferous leach liquors. Dilute sulfuric acid solutions containing 0.3 mg. of thorium and 100 mg. each of cobalt(II), chromium(VI), copper(II), iron(", molybdenum(VI), nickel(I1) vanadium(IV), and uranium(S'1) and 5 mg. of titanium(1V) were added to columns of 15 ~
nil. of IR-120 resin. The columns were washed with 150 nil. of 2-M hydrochloric acid and spot tests showed that the ions were being elut’ed. The thorium was then eluted, and analysis of the eluate showed no error, within experimental limits, from the presence of the respective int,erfercnces. The emluation of interferences was limited to the examination of elements which might’ be in the samples to be analyzed. The cation exchange separation procedure should provide some separation from t r i d e n t yttrium, lant8hanum,and rare earths. Hon-ever, the qundrivalent elements such as zirconium anti hafnium would tend to follow thorium closely. Results. -4s there was no standard uranium ore of knon-n thorium concentration available. a known amount of standard thorium solution was added t o aliquots of solutions from four different types of uranium ores. Aliquots of t h e ore solutions, .rvith and without’ added thorium, were analyzed 1y, the recommended procedure. The results of this test, shown
(5) Dyrssen, D., Svensk Kern. Tidskr. 62, 1.53 (1950). (6) Gordon, L., Firsching, F. H., Shaver, K. J., As.4~. CHEM. 28, 1476 (1956). ( 7 ) Guest, R. J., Can. Dept. Mines and Tech Surveys, Topical Rept. TR-98 (1952). ( 8 ) Kraus, K. A4,, Moore, G. E., Pielson, F.. J . Am. Chem. SOC.78. 2692 (1956). (9) Kraus, K. A,, Nelson, F., Proc.
Table Ill. Test of Cation ExchangeSpectrophotometric Method
Ore Type Lignite Dyson Rum Jungle Lukachukai
Thorium, Mg. RecovAdded Found ered 0 489 0 5L4 Sone 0 025 0 589 0 489 0 488 Sone Sone 0 488 0 489
Sone Uranium 0 489 concentrate Sone
0 474
Sone 0 479 Sone
0 474
0 479
Intern. Cons. Peaceful Uses Atomic Energy, Geneva 1955 7, 113 (1956). (10) Xlenis, O., Manning, D. L., Goldstein. G., .\NAL. CHEM.29, 1426
(1957).
\
in Table 111, indicate a good recovery of thorium. LITERATURE CITED
Bane, R. IT., U. S. Atomic Energy Comm., CC-3336 (1945). Banks. C. V.. Rvrd. C. H.. .\SAL. C H E 25, ~ 416 il9b3). ’ Brown, R’. E., Rieman, FY., J . A4t?i. Chern. SOC.74, 1278 (1952). Cuttitta. F., U. S. Geol. SurvelTEI-498 (1955).
’
i l l ) Radhakrishna. B. P.. Anal. Chirn. Acta 6,351’(1952).’ (12) Samuelson, O., “Ion Exchangers in I
-4nalytical Chemistry,” p. 35, Wlev, New York, 1953. (13) Smith,“RI. E., U. fi. Atomic Energy Comm., LA-1897 (1955). (14) Thomason, P. F., Perry, XI. b., Byeriy, K. RI., -1s.4~. CHEJI. 21, 1239 (1919). RECEIVEDfor review July 11, 1957. Xccepted February 16, 1958. The Raw Materials Development Laboratory is operated by the National Lead Co., Inc., for the U. S. Atomic Energy Commission. Work carried out under Contract No. AT(49-6)-924.
Chromatography of Amino Acids on S uIfo nuted Polystyrene Resins An Improved System STANFORD MOORE, DARREL H. SPACKMAN, and WILLIAM H. STEIN The Rockefeller lnstitute for Medical Research, New York 2 7, N. Y.
b Improved procedures have been developed for the chromatographic determination of amino acids on columns of finely pulverized 8 cross-linked sulfonated polystyrene resins. The use of a smaller particle size has permitted faster flow rates, and appropriate choice of eluents has simplified operations. Complete analyses of protein hydrolyzates can b e performed in about 48 hours with fraction collectors and in 24 hours with automatic recording equipment. The same system, with minor modifications, can b e used for determination of amino acids and related compounds in blood plasma, urine, and animal tissues.
70
in the earlier ion exchange procedures (8.9) make possible a complete amino acid analysis of a peptide or protein hydrolyzate in 24 to 48 hours. The modified system can be used either with a fraction colOUIFICATIONS
lector or with automatic recording equipment (1.2, IS). The method (in its manual and automatic forms) has been used for analyses reported in recent studies on histones ( I ) , hemoglobin ( I 6 ) ,and ribonuclease ( 5 ) . I n order to use a faster flox rate Ivithout undue broadening of the peaks 16), a resin of smaller particle size has been utilized. Improved resolving power and speed have been attainable with columns packed with a very finely pulverized 8% cross-linked sulfonated polystyrene resin; Amberlite IR-120 in “micropowder” form has shown good reproducibility from batch to batch over a 3-year period of test. The commercial polvder has been classified into fractions possessing the desired ranges of particle size by the hydraulic method recently described by Hamilton (2).
The mode of operation of the columns combines features dratvn from both the Dowes 50-X8 (8)and 5O-X1 (9)
methods. The neutral and acidic amino acids are separated on a 15O-cni. column of hmberlite IR-120, and the basic amino acids are applied to a 15em. column. The t n o columns may he used repeatedly nithout having to be repoured. A single temperature of operation (50” C.) has proved possible. Only two buffers are required with tht. 150-cm. column, necessitating one change of eluent. A single buffer is employed for the elution of the basic amino acids from the 15-em. coluniri, making possible a stable base line throughout the analysis. The eWuent curves obtained when a synthetic mixture of amino acids is analyzed by this procedure are shorsn in Figure 1. Except v, here noted, the directions in this insnuscript apply when the columns are used with fraction collectors. EXPERIMENTAL
Resin.
T h e finely ground sodium
VOL. 30, NO. 7, JULY 1958
1185
