DISCUSSION
The proposed procedure I\ as satisfactory for Ioutine analyses of animal tissucs. For large samples of bone (over 2 grama) the brnzohydro~amic acid complexes of both iron and vanadium should br extracted hrst from the aqucxous solution a t pH 3.0, a t n hich calcium prwhlorittc. rvmains in solution ant1 facilitatc. the, qeparation of vanadatc from calcium Separation of thc tr\ o coniplrv=s is thcn carried out subscquently as indicatcti above. 'I%(> pre-cutmetion of the iron com-
plex of benzohydroxamic acid above pH 8.5 avoids the more tedious removal by electrolysis (2, 5 ) . The removal of titanium extends the applicability of this procedure t o feed, feces, and plant material. ACKNOWLEDGMENT
The author is grateful to Camillo Artom for his interest and help in the preparation of this paper. LITERATURE CITED
(1) Das Gupta, A . K., Singh, 11. &I.,
J . Sci. Ind. Research ( I n d i a ) 11B, 268 (1952). (2) Jones, G. B., Watkinson, J. H., ANAL.CHEM. 31. 1344-57 (1959). (3) Jones, L. W.,'Hurd, C: D.,'J. Ani. Chem. Soc. 43, 2422 (1921). ( 4 ) Smith, G. F., Anal. Chim. Acta 8 , 39i-421 (1953).' 15) . 25. . , Talvitie. N. A,. A N ~ L CHEK 604-7 (1953). (6) Wise,' W.'M., Brandt, IT. iY.,Ibid., 27,1392-5(1955).
RECEIVED for review January 28, 1960. Accepted April 7, 1960. Work supported in part by grants from the United Medical Research Foundation of Xorth Carolina and the h-ational Multiple Sclerosis Society.
An Ion Exchange Selectivity Scale of Cations Based on Equilibrium Distribution Coefficients F. W. E. STRELOW Nafionul Chemical Reseurch Laborajory, South African Council for Scientific and Industrial Research, Pretoria, South Africa
b A table of equilibrium distribution coefficients, K d , for 43 cations in hydrochloric acid using the cation exchange sulfonated polystyrene AG 50W-X8 resin i s presented. K d values at various hydrochloric acid concentrations are included. The cations are arranged in a selectivity scale according to the numerical value of K d in 1.ON hydrochloric acid. Relations between K d values and elution curves, and K d values and tailing are discussed.
as used by Tompkins and -\layer (IO), and Schindewolf (8). This coefficient is not a constant like K ( d ) , but changes with compositions and concentrations of the reagents in the water phase, the nature of the resin. and the amount of cation to amount of resin ratio in the exchange systern. Temperature and pressure have a lesser influence. hlaj er and Tompkins (5,lO)developed the equation 2i = A- X
ma^ of dry resin in the column)
I
ON EXCHAXGE and ion exchange chromatography have gained extensive use in analytical and preparative chemistry during the last two decades. One of the basic concepts of cation exchange is that of affinity. Bonner ( 2 ) and his group detcrmined affinities for about 25 cations for Dowe.; 50 resin using the rquilibriuni constant K developed by Argersinger ( 1 ) and coworkers. The cations were arranged in an affinity scale according to the numerical value of K. Affinities are of limited use for the prediction of the column euchange behavior of a cation because they do not take account of the influence of the aqueous phase. More specific information about the behavior to be expected from a cation in a column elution esperiinent is given by the equilibrium distribution coefficient
K,,
=
iiniourit of ion on resin X volume of water phase, ml. amount of ion in water phase X gram dry resin (1)
(2)
where 1' stands for the volume of the eluting agent, in milliliters, which has to be passed through the column to elute the maximum of the elution peak. Good agreement was found between experimental and theoretical elution curves when the cit'rate conipleses of the rare rarths were a t tracer concentrations, and it seems reasonable to assume that the equation will apply to other cations as n ~ l l . The equation is valid only when the total amount of thc cation is less than about 3% of the total column capacity ( 3 ) . The equation shows that an increase in the ratio of the distribution coefficients K d of t\vo cations will result in an increasc of the ratio of the maximum peak elution volumes. 01/2i2. This ratio is called the separation factor, cy, and must be considered the most important parameter in ion exchange chromatography. Obviously a table of numerical values of K d for cations or, alternatively, plots of K d againEt concentration of eluent, as supplied by
Kraus ( 4 ) and his coworkers for the chloride complexes in anion eschange chromatography, nould be a valuable tool for the analytical chemist. No equivalent to their work seems to be available for cation cxchangc. chromatography. A comprehensive study of distribution coefficients of cations in hydrochloric acid was therefore undertaken and the relations between distribution coefficients and elution curvc's were investigated for a large number of cations. Up to no\v the work has been limited to the use of one resin, the AG 50 sulfonated polystyrene processed from Donex 50 by the Bio-Rad Laboratories, Berkeley, Calif. EXPERIMENTAL
Equilibrium Distribution Coefficients. Portions (2.5-gram) of B G 50W-X8 100- t o 200-mesh resin in t h e hydrogen form and dried to cons t a n t weight at 105' C., were weighed out accurately and transferred into 500-ml. Erlenmeyer flasks; 20 ml. of a standardized solution of the cation in I N hydrochloric acid was added, followed b y 230 ml. of distilled water and/or the right amount of standardized hydrochloric acid to give a final volume of 250 ml. of hydrochloric acid of the desired concentration. The flasks were stoppered and shaken in a mechanical shaking device for 24 hours (48 hours for thorium) at room temperature. The resin was then separated from the aqueous phase by filtration, and care was taken t o let it drain completely before the flask and filter were washed twice with distilled water. VOL. 32, NO.
9, AUGUST 1960
1185
These washings n'ere omitted in the case of the alkali metals. The amount of cation in the total aqueous phase combined with the washings was determined by an appropriate method, and as a check the amount in the resin was determined also after the resin had been ashed, whenever this was possible. Column Experiments. Borosilicate glass tubes, 70 cm. in length and 1.15 em. in diameter and sealed a t t h e bottom with fused-in sintered glass filters of medium porosity, were used as columns. T h e tops were fitted with 500-ml. dropping funnels connected by ground-glass joints to the columns. Weighed amounts of dried resin were treated with 1 to 1 hydrochloric acid, shaken for some hours in a mechanical shaking device, and transferred to the columns after most of the acid had been replaced by distilled water. Before use the resin columns were freed from acid by washing viith 50 ml. of distilled water. During the experiments the flow rate was kept at 2.5 + 0.5 ml. per minute for columns containing 10 grams of dry resin, and 1.2 + 0.2 nil. per minute for
columns containing 20 grams of dry resin. DISCUSSION
As a result of the u-ork, a table of Kd values was prepared for 43 cations. The numerical value of K d in 1.ON hydrochloric acid for a total _____ anwuiit of cation total resin capacity ratio of 0.4 vas chosen arbitrarily to arrange the cations in a selectivity sequence, in n-hich they are presented in Table I. As the cation-resin ratio is an important quantitj-, it is given the symbol q where total amount of cation in exchange system in equivalents Y = - - total resin capacity in equivalents The high values of q in the above experiments were chosen for practical analytical reasons. The experiments were conducted in duplicate and in some significarlt cases in triplimte to cnqurc accuratc rewlts.
Table I. K d Values a t Different Normalities of Hydrochloric Acid 3.0 2.0 Cation 1 0 0.1 0 2 0.5 61 ZrO +Y 7250 489 -105 > 1oj > 105 114 239 2049 Th+4 -106 > 105 > 105 18.8 48 La+3 > 105 105 265 1 2480 18.8 48 105 > 105 264 8 Ce + 3 2460 13.6 29.7 Y+3 144 6 1460 > 1oj > 10' 18.5 36 126 9 Ba + 2 2930 > 104 590 19.2 33 Hg+ a 94 2 640 > 104 7600 4.7 12.5 ~1+3 1900 8200 60 8 318 10.0 17.8 6r +2 217 4700 60 2 1070 3.2 7.75 Ga+3 42 58 260 >lod 3036 7.3 12.2 42 29 Ca +z 151 3200 700 6 ,8 9.8 Pb+2 a '35 66 1420 > 104 183 3 .6 5.2 35 45 Fe+3 225 9000 3400 4.8 7.9 Cr f 3 26 69' 262 1130 73 5.8 9.9 TI+ 22 32 41 173 91 4.7 7.2 Ni + 2 21 85 1600 450 70 1.2 6.7 21 29 Co +* 72 1650 460 3.5 6.2 Mg +2 20 99 1720 88 530 :3 . 9 6.0 &In+ 2 20 17 2230 84 610 2.7 4.1 Fe +* 66 19 77 370 1820 ... 10.4 cs +I 44 19 41 99 182 4.9 7 :3 19 20 UOZ +4 102 5460 860 5.4 7. 9 Ag+ a 35 18 08 156 83 2.8 4.3 17 50 cu+2 65 1510 420 3 .9 R .9 Hg+2 a 1090 121 16 85 4700 2.4 Xi 16 03 Ln +e 64 1850 510 ... 15 43 8.I Rb 33 120 7% . . 7.4 13 87 29 K+ 106 64 :3 . 3 5.2 42 Be+z 117 13 33 255 2,4 :3 . 7 Ti+' 11 86 39 > 10' 297 , . . ... 7 20 230 v +4 44 . . 3.6 ru'a + 52 12 5 59 28 3 ... 2.5 Li .3 83 18 9 33 8 1 ... 1.2 1 60 Sn+4 6 2 -10' 45 1.0 0.6 6 5 1 54 Cd + 2 84 510 0.2 0.7 I 10 5 0 13 9 V+s 7 0 0.2 0.4 0 3 Mo +j 10 9 45 0 81 . . . 1.0 0 8 Se +' 1 1 0 63 0 6 1.0 1 0 1 0 Ri +3 Ppt. Ppt. 0.1. An inspection of Table I11 shows that a t Q = 0.1 the K d value for thorium is much higher than that for zirconium, and it will probably reach extremely high yalues for very small values of Q. In I T hydrochloric acid for ‘1 = 0.01, Kd >lo6. Thorium s~erristo behai-e in t i singular way in this aspect, RP none of the other
(1) Argersinger, W. L., Davidson, A. W., Bonner, 0 . D., Trans. Kansas dead.
scz. 53,404 (1950). (2) Bonner, 0. D., Jumper, C. F., Rogers, 0. C., J . Phys. Chem. 62, 250-3 (1958). (3) Cornish, F R , ilnalyst 83, 634 (1958). (4) Kraus, A , Selson, F., International Conference on the Peaceful Uses of Atomic Energy, paper S o . 837, Geneva, 1955. (5) XIayer, S W , Tompkins, E. R., J . Am. Chem. Soc. 69, 2866-74 (1947). (6) Reichenherg, D., McCauley, D. J., J . Chem. SOC 1955,2741. (7) Robinson, R. A,, Stokes, R. H., “Electrolyte Solutions,” pp. 491-501, Academic Press. Ken, York. 1955. (8) Schindewolf, G,) Anqem. Chem. 69, 226 (1957). (9) Sen Sarma, K.S., hnders, E., Miller, J. AI.. J . Phus. (’hem. 63, 559-65 (1959); (IO) Tompkina, E. R., l\Iayer, 6. IT.> J . A m . Chem. Soc. 69, 2859 (1947).
RECEIVEDfor review January 25, 1960. Accepted April 26, 1960. Abstracted from work done for a D.Sc. thesis at the Department of Inorganic and Analytical Chemistry at the University of Pretoria, Pretoria, South Africa.
