hydroxylamine and hydroxamates in mixtures, as outlined in this paper, is based on the fact that hydroxylamine gives a color reaction by Blom’s method, both a t p H 2.3 and 3.7, and the hydroxamates react only a t p H 3.7. Because nitrite, the oxidation product of the two substances, gives full color a t both pH values, it follows that hydroxamate can only be ovidized by iodine to nitrite under less acid conditions. Therefore, to obtain a quantitative oxidation of the hydroxamate, it is essential to secure and maintain a p H of 3.7 for the duration of the oxidation reaction. K i t h hydroxylamine, the oxidation reaction is not impaired by the high hydrogen ion concentration (pH 2.3). The differences in the electrolytic dissociation of the two substances perhaps explain this phenomenon. Thus, a t p H 3.7 we get the total amount of hydroxylamine and hydroxamate present in the mixture, while by performing the same
procedure at p H 2.3, only hydrosylamine is being determined. However, while the color development a t p H 2.3 is rapid, the reaction rate is considerably slower a t pH 3.7. Kevertheless, the reaction with hydroxamate can proceed as rapidly as that of hydroxylamine if the pH of the reaction mixture is lowered to 2.8 after osidation. Calibration curves for nitrite, hydroxylamine, and 0-aspartyl hydroxamic acid (Figure 2) show that equivalent amounts of the three substances give practically the same color intensities, indicating that the oxidation of hydroxylamine and hydroxamate to nitrite is quantitative. This justifies the use of the method suggested here. The amount of hydroxamate present in a mixture is obtained by subtracting the amount of hydroxylamine found a t p H 2.3 from the total amount of nitrite determined a t p H 3.7. The simultaneous determination of
hydroxylamine and hydroxamate should be valuable in studies of biological oxidation of ammonia ( 5 ) , nitrite reduction (Y),and other reactions where, in addition to hydroxylamine, hydroxamates may be formed as intermediary metabolites. LITERATURE CITED ( 1 ) Berginnnn, F., Segal, R., Biochem. J . 6 2 , 5 4 2 (1956). ( 2 ) Blom, J., Ber. deut. chem. Ges. 50, 121 (1926). ( 3 ) ,Feigl, F., “Spot Tests,” Vol. 2, Elsevier, London, 1954.
(4) Grossowicx, N.,
Halpern, Y. S., J . B i d . Chem. 228, 643 (1957). ( 5 ) Hofman, T., Lees, H., Biochem. J . 5 4 , 5 7 9 (1953). ( 6 ) Lipmann, F., Tuttle, L. C., J . Rid. Chem. 159, 2 1 (1945). ( 7 ) Zucker, If.,Yason, A , , Ihid., 213, 463 (1R55).
RECEIVEDfor review J ~ l y 14, 1958. Accepted Kovember 23, 1959.
Adsorption of the Elements from Hydrofluoric Acid by Anion Exchange J. P. FARIS Argonne National laborafory, lernonf, 111.
b Elution characteristics for some 50 elements in a hydrofluoric acid medium were studied with a strongly basic anion exchange resin. Estimates of distribution coefficients in 1M to 24M acid were obtained by spectrographic analysis of column effluent solutions. The adsorption data observed for elements in this medium suggest many possible analytical separations.
W
ITHIX recent years the availability of stable high capacity ion exchange resins has led t o the rapidly increasing use of these materials in the analytical field. The added emphasis on ion eschang? methods of separation is evidenced by the number of detailed quantitative procedures and variety of applications being presented in the literature. The various materials available, the techniques employed, and development of the theory are described in the manufacturers’ literature, periodical review articles, and several recent books ( 7 , 9 ) . Anion exchange resins have proyed to be extremely useful for performing rapid quantitative separations. The comprehensive survey of adsorption characteristics in a hydrochloric acid
520
ANALYTICAL CHEMISTRY
medium presented by Kraus and Kelson (6) has resulted in a variety of analytical applications. Anion exchange data have also been presented for a number of the metals in nitric acid ( 1 , 2, 6, IS) and hydrochloric-hydrofluoric acid mixtures (5, IS). Hydrofluoric acid (IO), sulfuric acid (2, 5 ) , and phosphoric acid ( 4 ) systems have been reported less extensively. T o extend the scope of anion euchange-analytical separation methods and also to provide a basis for planning future experiments in acid mixtures, a general survey of the metals in a hydrofluoric acid medium was undertaken. Spectrographic analysis of the column effluent was attractive because the rapid simultaneous determination of many elements could be made and radioacthe tracers \\-ere not necessary. Results presented in this surrey were obtained by visually estimating quantities of each element found in effluent fractions from their spectral intensity. The individual determinations, while not estremely accurate in themselves, were used t o draw elution curves representing the flon- from the column; because the beginning and the end of the curves could be readily seen, the peak could usually be estimated to m-ithin several
column volumes, and approximations made as to the general shape of the curve. The principal advantage of spectrographic analysis is demonstrated in the fact that over 60 element species were studied in a few months. MATERIALS AND PROCEDURE
Resin. -4 large batch of Dowex 1-X10, 200-mesh anion exchange resin n-as converted from the chloride form b,y washing with hydrofluoric acid until a silver nitrate test for chloride 11as negative. Analytical grade resin (supplied by Bio-Rad Laboratories, Inc., Berkeley, Calif.) was found to be sufficiently free of foreign material to require no further purification. The rated capacity was 3 meq. per gram and the approximate density, determined from the displacement of benzene by the oren-dried resin, was 1.67 grams per cc. Columns. Eight polyethylene columns inch in inside diameter, each containing 2.8 grams of oven-dried resin, were used for the initial survey. T h e resin was introduced to t h e columns from a dilute hydrofluoric acid slurry and retained by finely ground polyethylene packed in the lower tip. Each column \\as used for a selected molarity of hydrofluoric acid throughout. Concentrations of 24, 20, 16, 12,
NO ADS SL ADS
- NO ADSORPTION FROM - SLIGHT ADSORPTION
I M - 2 4 M HF
STR ADS -STRONG ADSORPTION LOG DIST COEFF
MOLARITY HF
>2
R O M A N N U M E R A L S R E F E R TO OXIDATION STATE IN I N I T I A L SOLUTION
8, 4, 2, and 1X were chosen. The of which n a s replaced after 15 ml. height of the settled bed was about 20 (approximately 4 column volumes) rm., the bed volume slightly less than had been collected. As a rule, a new 0 cc. Solutions were allowed to flon group of elements n a s added after two through the resin by gravity, giving 15-ml. portions had been collected from flow rates of 8 to 10 ml. per hour. -111 the previous addition. Although the experiments were carried out a t room flow was interrupted from time t o time, temperature. it was felt that no appreciable error Solutions. A number of stock solu\\as introduced. The liquid level retions 1% ere prepared. Each contained mained near the top of the resin befrom one t o 12 elements dissolved in cause of capillary action within the dilute hydrofluoric acid, T h e introcolumn. During the investigation the duction of anions other t h a n fluoride resin in the columns was replaced n h e n \\as avoided by dissolving a metal, necessary to avoid mixing of oxidation oxide, carbonate, etc ., in hydrofluoric states. acid. Whenever other acids were used, Analysis. Spectrographic estimaas in the case of some platinum metals, tions were made of t h e elements in the solution was repeatedly taken t o t h e effluent b y t h e copper spark dryness with hydrofluoric acid before method ( 3 ) . Each 15-ml. fraction dilution t o volume. ‘The concentration n a s reduced to a volunie of 2 ml. by of each element n-as such that a 0.1-ml. evaporation under heat lamps. Alialiquot of the stock solution contained quots of 0.1 ml. of each solution were several hundred times the least amount then placed on copper electrode pairs, detectable in the subsequent effluent. evaporated to dryness, and sparked in The amount per aliquot ranged from the appropriate wave length regions 0.1 y for beryllium t o 500 y for phosunder standard conditions. A 0.1-ml. uhorus and for most elements n a s 10 portion of the original stock solution i o 4 0 y. diluted to 2 ml. was exposed a t the same Procedure. Aliauots of 0.1 ml. of time to serve as reference. Graphite a stock solution w&e diluted to about electrodes were used for the determina3 nil. 11-ith each molarity of hydrotion of copper. Individual determinafluoric acid and introduced t o t h e tions were estimated to be accurate rmpective columns. After t h e l e ~ l within +507, of the amount present. of the liquid in a column reached the top of the resin bed, hydrofluoric acid of RESULTS the proper molarity was added to the column. The effluents were received in Results for the elements inrestigated calibrated polyethylene containers, each in the hydrofluoric acid system are pre-
sented in Figure 1. Elements nhich came through quantitatively in the first 15 ml. of effluent are indicated by “no adsorption.” If> in addition, a trace appealed in the second effluent fraction it is indicated by “slight adsorption.” “Strong adsorption” denotes a n element not detected in any elution fraction. Distribution coefficients for each ionic species n ere derived from the estimated locations of the elution curve peaks. The approximate percentages of each element found in every 15-ml. effluent fraction were used t o plot corresponding elution curves. Tompkins (11, 12) and hIaycr (8) have shon n that the number of colunin volumes, F, which ha\-e passed through the column nhen the peak of the elution curve is reached is nuniericnlly equal to the distribution, C, bet n een the solution and the resin (F,,, = C). Also they proved that the relationship Kd = C x t ’m is valid for any ratio of solution volume to resin n eight n here
1’
=
u =
F
=
m
=
volume of effluent volume of liquid phase in colunin number of c’s that have passed through column, or T’ ’2’ mass of resin
Substituting To/; for C in the above, = T7/m is obtained. Thus the distribution coefficient values in Figure 1 Kd
VOL. 32,
NO. 4, APRIL 1960
521
a r e the ratios of the peak of the elution curve in milliliters to the grams of resin in the column. The actual measured volume was corrected for the first column volume of displaced liquid and the method of adding the standard solutions to the column by subtracting 5 ml. The assumption was made that equilibrium conditions existed during the operation of the columns, because the loading was low with respect to resin capacity, the flow rates were low, and the length of the column mas sufficient to provide a large number of theoretical plates. The correctness of this assumption was further borne out b y the observation that the majority of the elution curves were symmetrical. T o estimate the reproducibility of the method, additional elution curves for a number of elements were determined at selected hydrofluoric acid concentrations. Smaller columns (3/16 inch in inside diameter) containing either 1 or 2 grams of resin were used and effluent portions of 5 ml. taken for analysis. Variation of distribution coefficients derived from the spectrographic analysis was found to be generally not greater than lo%, with the exceptions later discussed. Because the gallium(II1) results were appreciably different from those reported (IO),a radiochemical determination was made of the elution of 78-hour gallium-67 tracer. I n lM, 2M, and 4&f hydrofluoric acid solutions adsorption of the activity was negligible, confirming the spectrographic results. A distribution coefficient of approximately 5.5 was found for gallium in 0.4M acid. DISCUSSION OF RESULTS
Valence states given in Figure 1 are those of the element when added to the column. While no attempt was made to determine oxidation state changes after being in contact with the resin, several elements gave evidence of reactions other than simple exchange. A lack of a definite peak in the elution curve, poor reproducibility, loss of color, random breakthrough, and excessive tailing were all indications of oxidation or reduction occurring within the column, Dotted lines are placed on the chart for elements which did not produce definite peaks in their elution. These curves n-ere generally less reproducible. The loss of color when manganese(VI1) and chromium(V1) compounds were added to the resin is evidence that these elements could have been reduced before being eluted. Tin (11) and titanium(II1) were probably oyidized during the experiments, as their elution was identical to that of tin(1V) and titanium(1V). The above observations point out the likelihood of strong oxidizing agents reacting with the resin, thereby being reduced, and the possibility of reducing agents such 522
ANALYTICAL CHEMISTRY
24
, A ,I-- %L
; I 55
75
Figure 2. tantalum
95
i
,1 ,;FL.L2*--
t
-
L
155
-_I4
-
-
-~
-
215 235 EFFLUENT COLUMN VOCUMES
_- -
2 j 5 p z i 5 - > ~ ~ 5 L 5 355
Elution curves showing separation of niobium and
-
Ta --- Nb
as phosphorus(1) and iron(I1) being eluted in a n oxidized state. Analytical procedures concerning any of the above group of elements should be given careful attention, because distribution coefficients could vary with resin loading and elution conditions. Chemistry of the platinum metals is complex and several uncertainties exist in the interpretation of the results. When palladium(I1) and platinum(1V) were added to the columns, they were strongly adsorbed, save that small percentages were found in a few effluents from the columns being washed with 8 N , 12N, and 16N acid. While rhodium (111) was eluted easily, rhodium(V1) gave indications of some reaction with the resin, because considerable tailing was noted. I n a n attempt to determine elution characteristics of iridium(II1) and iridium(1V) it was found that both were strongly absorbed in the lower acid concentrations but above 4M acid the breakthrough was somewhat erratic and the estimated yields were appreciably low, so that no distribution curves could be produced. The adsorbability of every element forming a n anionic complex in hydrofluoric acid decreased regularly with increasing acid molarity, with the exception of niobium. At about 16M hydrofluoric acid a n abrupt change in the curve for this element indicated the possible formation of a different ionic species. Elution curves of niobium and tantalum in several concentrations of acid are presented in Figure 2 to illustrate how either element can be eluted ahead of the other by proper choice of the acid concentration. Disadvantages of the method of analysis employed has led to several omissions in Figure 1. Because the analytical determination required evaporation of hydrofluoric acid solutions on copper electrodes, it was not possible to determine volatile fluorides of germanium and osmium. Mercury(I1) was not quantitatively recovered in all acid concentrations, probably because of losses due to volatilization. These results n-ere normalized for the amount recovered and the curve in Figure 1 was drawn accordingly The fluorides of several other elements are not sufficiently soluble to permit reliable analysis. The curves are not complete for elements nhich have a high affinity for
the resin, because the task of collecting the number of fractions required for their elution was prohibitive. Although data for elements having high distribution coefficients could be obtained with much smaller columns, other methods of determining adsorption would be advantageous. From a n examination of the adsorption characteristics presented in Figure 1 it is apparent that many separations can be made in a hydrofluoric acid medium with a n anion exchange resin. The analytical application should prove particularly valuable for quantitative separations n-hich include one or more of the elements niobium, tantalum, zirconium, tungsten, titanium, tin, and beryllium. ACKNOWLEDGMENT
The author thanks the several members of this laboratory who have been of assistance, in particular R. F. Buchanan for many valuable suggestions, and J. J. Hines for performing the radiochemical preparation and analyses. LITERATURE CITED
(1) .Buchanan, R. F., Faris, J. P., Orlan-
dini, K. -4., Hughes, J. P., U. S. Atomic Energy Commission, TID-7560 (1958). (2) Bunnev, L. R., Ballou, N. E., Pascual, J., Fot< S., AKAL. CHEX 31, 324 (1959). (3) Fred, M., Nachtrieb, Iy. H., Tomkins, F. S., J . Opt. SOC.Am. 37, 279 (1947). (4) Freiling, E. C., Pascual, J., Delucchi, A. A,, ANAL.CHEM.31,330 (1959). (5) Kraus, K. A , , Nelson, F., ASTM Spec. Tech. Pub. N. 195, 27 (1958). (6) Kraus, K. A, Xelson, F., Proceedings,
International Conference on Peaceful Uses of Atomic Energy, Vol. 7, p. 113, United Nations, 1956. (7) Kunin, R , “Ion Exchange Resins,” 2nd ed., Wiley, Xew York, 1958. (8) Mayer, S. R., Tompkins, E. R., J .
Am. Chem. SOC.69, 2866 (1947). (9) Nachod, F. C., Schubert, J., eds.,
“Ion Exchange Technology,” Academic Press, New York, 1956. (10) Schindewolf, U., Irvine, J. W., Jr., AN4L. CHCM. 30, 906 (1958). (11) Tompkins, E. R., J . Chem. Educ. 26, 32, 92 (1949). (12) Tompkins, E. R., hlayer, S. W., J . Am. Chem. SOC.69, 2859 (1947). (13) Wish, L., ANAL. CHEW 31, 326 (1959).
RECEIVEDfor review RIay 15, 1959. Accepted January 21, 1960. Work performed under the auspices of the U.S. Atomic Energy Commisslon.
