six samples has been tabulated as follows : Extraction of samples Concentration of extracts Transfer of extracts and GLPC Total
Hours 4 1’/2 1
61/2
With the method employing column chromatography and subsequent ultraviolet spectrophotometry, 8 hours were required to process two samples on a comparable man-hour basis. The gasliquid partition chromatography method therefore represents a considerable saving in analytical time. USE O F GAS-LIQUID PARTITION C H R O M A T O G RAPHY FOR ANTIOXIDANT IDENTIFICATION
Because the retention time of a given compound may vary when measured on two different substrates ( 6 ) . the relative retention time on two different substrates can be used as a method of resolving mixtures of antioxidants. I n Table 111, the retention times for various antioxidants, as well as three vanillin masking agents, are given for silicone and propylene glycol substrates
when operated under conditions previously described. Gas-liquid partition chromatography is a useful method for the qualitative analysis of unknown antioxidants and their mixtures but retention times should be compared on two different substrates to avoid the possibility of confusion between compounds which may have closely corresponding retention times on a given substrate.
may be used for the specific identification of antioxidants and masking compounds, but it is advisable to compare retention time on at least two different substrates.
SUMMARY
(3).hlellon, M. G., “Analytical Absorp tion Spectroscopy,” pp. 395-7, Wiley, Kew York. 1950.
Gas-liquid partition chromatography may be applied to the concentrated cyclohexane-isopropyl alcohol extract of 2,B-di-tert-butyl-p-cresol from treated paperboard. Recoveries of 100% were obtained of known amounts of t h e antioxidant from treated paperboard with a deviation of not more than = l o % for a treatment range of antioxidant from 14.4 t o 144 mg. per square foot or 0.05 to 0.5% by weight of board. The over-all time required to process six samples is 6l/, hours, which represents a substantial saving in time over previous methods. The gas-liquid partition chromatography retention time
LITERATURE CITED
(1) Anglin, C., Mahon, J. H., Chapman, T. A., J. Ag. Food Chem. 4, 1018 (1956’1.
\----,-
(2) Jennings, E. C., Jr., Edwards, D. G., A N A L . CHEM. 25, 1179 (1953).
(4)Modern ‘Packaging 29, KO. 5, 118
(1956). (5) Phillips, C., “Gas Chromatography,” p. TO, Academic Press, Kew York, 1956. (6) Phillips, &I. A., Hinkel, T. D., J . Ag. Food Chem. 5 , 379 (1957). (7) Shell Chemical Corp., Tech. Bull. SC : 55-43 (1955). (8) Shell Development Co., Emeryville, Calif., Emerpville Method Series, EMS 3 H 31/56B (1956). 1 (9) Snyder, R. E., Clark, R. O., ANAL. CHEM.22, 1428 (1950). RECEIVED for revieK February 14, 1958. .4ccepted June 30, 1958. Division of ilnalytical Chemistry, 133rd Meeting, .4CS, San Francisco, Calif., .4pril 1958.
Use of Ion Exchange Resins in the Analysis of Rocks and Minerals Separation of Sodium and Potassium LAURA E. REICHEN
U. S.
Geological Survey, Washington
25, D. C.
This procedure was developed primarily for analyses in which limited amounts of sample are available. Sodium and potassium can be separated from the other constituents of silicate rocks by cation exchange resin (Amberlite IR-120). The sample i s decomposed with hydrofluoric and SUIfuric acids and passed through the resin bed after expulsion of the fluorine. The column i s eluted with 0.1 2 N hydiochloric acid at a fast flow rate of 4 ml. per sq. cm. per minute and the sodium and potassium are recovered together within a reasonable time. Other constituents of the sample, except silica, can be determined on the same portion of sample.
C
exchange resins can separate sodium and potassium from the other constituents of a silicate rock, a i t h out the addition of reagents that interfere ATIOX
1948
ANALYTICAL CHEMISTRY
Kith the subsequent quantitative determination of those ions, as in the J. Lawrence Smith procedure ( 5 ) . The use of a resin makes possible a practically complete analysis on one portion of sample, inasmuch as the anions pass through the resin unchanged, and the remaining cations can be recovered from the column n i t h hydrochloric acid (10). K i t h ion exchange separation much less sample may be required for a complete analysis, and it is easier and quicker to perform than the J. Lawrence Smith procedure. Several methods using ion evchange resins for the separation of alkalies (1-3, 6, 7 , 11) are based on a very slow elution of 0.12 t o 0.5 ml. per sq. cm. per minute with weak acid. I n some analyses several days are required to complete an elution. Logie and Rayner ( 8 ) determined sodium and potassium in coal ash, but
the calcium and magnesium are eluted along with the alkalies. Sweet, Rieman, and Beukenkamp (la)determined the alkalies in silicate rocks, using cadmium oxide to precipitate the iron and aluminum before adsorbing the cations on the column from 0 . 7 s hydrochloric acid solution, as well as eluting with 0. hydrochloric acid. The procedure proposed is simple. After the sample has been decomposed with hydrofluoric and sulfuric acids t o volatilize the silica and then the fluorine, the cations are adsorbed on the resin. The sodium and pofassium together are then eluted rapidly (about 3.5 hours with the column used in this method) with 0 . 1 2 s hydrochloric acid, the eluent is evaporated to dryness, and the alkali chlorides are weighed. The alkalies can then be determined by flame photometry, tetraphenylboron, or chloroplatinic acid.
APPARATUS A N D REAGENTS
Ion Exchange Column. A 50-ml. buret, 11 by 600 mm., is used. Because its cross-sectional area is so nearly 1 sq. cm., t h e milliliters per square centimeter per minute and t h e volume of effluent collected per minute can be considrred t h e same. A pad of glass wool is placed in t h e bottom of the buret and the buret is almost filled with water. A slurry of Amberlite IR120 (0.45- to 0.6-mm. grain size) resin is added, allowing a free fall of the resin grains, until the volume of the resin in the buret is slightly more than 10 ml. Fifteen milliliters or more of water are drained through the column a t full speed and the volume of the resin is noted. The addition of resin and rapid draining of water are continued until the bed volume is 10 ml. The capacity of this column is 10 meq. The resin is eluted n-ith 4N hydrochloric acid and rinsed with water until the eluent is only slightly acid-about p H 5 using indicator paper. Hydrochloric Acid Elutriants. 0.12 N , 10 ml. of concentrated hydrochloric acid diluted t o 1 liter; 0.46Ar, 40 mi. of concentrated hydrochloric acid diluted t o 1 liter, and 4 N , 1 t o 2 hydrochloric acid. Standard Solutions. -4aueous solutions of sodium a n d pota'ssium chloride and magnesium and calcium sulfates were standardized gravimetrically (6) and contained approximately 0.35 meq. per ml. Ferric and aluminum chloride solutions in 0.1-Vhydrochloric acid were filtered t o remove hydrolyzed material before being standardized gravimetrically. The titanium standard solution was made by fusing about 0.5 gram of titanium dioxide with potassium bisulfate, dissolving the melt in 5y0 sulfuric acid, precipitating the hydroxide with ammonia, and filtering. The precipitate was scraped into a beaker with a stirring rod as efficiently as possible and dissolved in 25 nil. of concentrated hydrochloric mid, diluted to 200 ml., filtered, and standardized gravimetrically. EXPERIMENTAL DATA
Because the behavior of a n element in an ion exchange resin bed is the same whether only t h a t element or several elements are present, provided that the column is not overloaded and there iq no interaction betm-een the ions, it mas possible t o work with only one element adsorbed a t a time on a column. Xeutral solutions of sodium and potassium sulfate were pas*ed through the columns and the sodiurii and potassium were adsorbed. The columns were then eluted with 0.12S or 0.46.1- hydrochloric acid, or by a stepmise elution using both concentration?. The combination of the two acid concentrations reduced the volume necessary to recover potassium. but some magnesium was also eluted.
Table I.
Effect of Acid Concentrations and Rates of Flow on Elution of Sodium, Potassium, and Magnesium
0.5 HCl, Mi. 0.12N
125 225 275-300 325-350 400
500
Flow Rate, Ml./Sq. Cm./Min. -4 0.5 2 4 0.5 4 % Sodium Eluteda % Potassium Elutedb % Magnesium Eluted 1
2
c
7
73
73 90 97 100
c
d
v
10
95 97 100
72 92 97
600
700 800 850 0.46.V 100
11
9
91 96 98
78 70 96 99 100
60 84
125
95 98
150 200 250
100
52
55
84
87 97 100
Xone 8
91 94
8
280.0 mg. adsorbed oxide. 121.1 mg. adsorbed oxide. c 13.0 mg. adsorbed oxide. d 68.0 mg. adsorbed oxide. e Magnesium is present in this volume of eluent.
*
Q
The use of 0.73- hydrochloric acid solutions suggested by Sweet and others (12) was not satisfactory for the small resin bed; the adsorption of titanium n a s not complete, and magnesium began t o show in the eluent before the recovery of potassium was complete. Their large resin bed with a volume of more than 200 ml. is not practical when the cations are t o be recovered for subsequent analyses. The per cent recovery of sodium, potassium, and magnesium under varying conditions is given in Table I. The rate of flow has no significant effect on the elution of sodium. Elutions were niade a t four different speeds--0.5, 1, 2, and 4 ml. per sq. cm. per minute-and in any given volume of eluent essentially the same per cent of sodium had been eluted. -4s expected, the slom-er the rate of flow the more efficient the elution of magnesium. The recovery of potassium was also affected by the rate of flow. The slower the flow the more efficient the elution a t the beginning and throughout most of the elution, until the tailing effect became apparent. PROCEDURE
Solution of Sample. Weigh a sample not t o exceed a total of 10 cation meq. Transfer t h e sample t o a platinum crucible and moisten 11-ith water, add about 10 nil. of hydrofluoric acid. cover tightly, and let stand on t h e steam b a t h 4 hours. Remove t h e cox'er a n d evaporate to dryness. Add 2 ml of 1 t o 1 sulfuric acid and about 25 ml. of water. Swirl the contents of the cru'cible to facilitate solution and evaporate to dryness, fuming off the sulfuric acid. Add 2 nil. of 1 to 1 sulfuric acid and water a second time. When all the salts but the insoluble
sulfates are in solution, again evaporate to dryness, fuming off all the sulfuric acid. Take the salts u p in 0.5 ml. of hydrochloric acid and about 25 ml. of water. Digest for 15 minutes. If there are insoluble sulfates present, remove them by filtering the solution through Whatman No. 42 paper and nashing the precipitate and paper thoroughly with hot water. Make the final volume to at least 50 ml. to obtain a solution no more than 0.1-V with respect to hydrochloric acid. Separation of Alkalies. Adsorb t h e cations on t h e resin by passing t h e solution through the column a t 2 t o 4 nil. per sq. em. per minute. Adjust the stopcock as t h e head of t h e liquid changes t o maintain a n even rate of flon throughout the exchange. Rinse t h e column with 100 ml. of water. t h e rate of flow can be speeded up somewhat (about A ml. per sq. em. per minute) for the last half of the rinsing. Elute the sodium and potassium by passing 850 ml. of 0.12N hydrochloric acid through the column a t 4 ml. per sq. cm. per minute. Evaporate the eluent to complete dryness. Add sufficient m t e r t o dissolve the sodium and potassium salts, transfer the solution to a Teighed platinum dish, and evaporate to dryness on the steam bath. Heat the dish cautiously over R loiv flame or electric heater until the danger of decrepitation is past. Increase the heat and rotate the dish over the flame until the salt? just melt. Cool in a desiccator and neigh as mixed chlorides. Dissolre the mixed chlorides in water. If the solution is not clear, d o not add a n y acid. This insoluble material ~vill be removed n-ith the ammonia precipitate. Using thymol blue indicator, neutralize the solution with ammonium hydroxide and digest on the steam bath for 30 minutes. If no precipitate forms, the first \\-eight is used as the final one. If there is a precipitate, filter through TThatman S o . 40 paper and wash the VOL. 30,
NO. 12, DECEMBER 1958
1949
Table II.
Sample 1 Pirssonit,e
2 Gaylussite 3 Northupite 4a Feldspar, 4b KBS 99 5a Opal glass, 5b NBS 91 6a Granite,
6b USGSG1 7a Diabase,
7b
USGSTT’1 8a Std. Xa s o h .
Results Obtained Using Proposed Procedure
X!eq. Wt. of in Sample, 1 G. G.
16 13 20 11
15
0.2500 0.2500
0.2500 0.5000 0.5000 0,5000
0.1202 0.0987 0.1731 0.1044 0.1057
0.5000
12
0.5000
0.0743
0.5000 22
0.2500 0.2500
0.0125 0.2240
8b 9a
9b
Std. K s o h .
0.1911
precipitate and paper thoroughly with a 2% ammonium chloride solution to which a drop of ammonium hydroxide has been added. Catch the filtrate in a weighed platinum dish, evaporate to dryness, and carefully fume off the ammonium chloride. Heat the mixed chlorides as before, cool in a desiccator, and weigh. RESULTS A N D DISCUSSION
The results obtained by this procedure are given in Table I1 for standard solutions, silicate rocks, and minerals. The samples of pirssonite [NazCa(co&.2H,O], gaylussite [Na&a(CO&. 5H20], and northupite [lTashlgC1(CO,),] are from the Green River formation in M7yoming and were carefully hand-picked. The granite and diabase were chosen for analysis because they are the rocks that were used in the survey’s study of the precision and accuracy of a chemical analysis (4). The mean standard deviation for the alkali chlorides calculated from the data in Table 14 (4) on the basis of a gram sample is 0.0052 gram, for alkali oxides 0.0030 gram. The precision for the mixed chlorides on the duplicates analyzed by the proposed procedure is well within this limit. When the amounts present are compared with the amounts found, although the variation is slightly more, the accuracy may also be considered satisfactory. The milliequivalents in 1 gram of sample and the aliquot of the sample actually analyzed are given in Table 11. If the ratio of the alkalies to the rest of the sample requires that a larger aliquot be used, the amount of resin can be increased, with a proportional increase in the volume of reagents. The amount of
1950
ANALYTICAL CHEMISTRY
0.1200 0.0981 0.1725 0.1033 0.1022 0,1054 0.1041 0.0744 0.0737 0.0122 0 0122 0 2238 0.2243 0.1900 0.1898
0.46
25.61 20 93 36.73 10.73
25.45 20 80 36 59 10.59
3.25
3.44
8.48
8.29
5.51
5.70
3.26
3.12
0.68
0.64
2 07
2.05
0.00 0.00 0.00 0 41
0.00 0.00 0.00
resin necessary is controlled by the milliequivalents to be adsorbed, but the volume of rinse water and eluent are a function of the amount of resin. If more resin is required, it would be advisable to use a column with a larger diameter-such as the tube used in a Jones reductor-to keep the time required to pass the increased volumes through the resin beds within reasonable limits. Finally the mixed chlorides were checked for purity by comparing weights before and after the ammonia precipitation. The samples of pirssonite, gaylussite, northupite, feldspar, opal glass, and granite 6a had no discernible precipitate and no change in weight. Granite 6b contained 1.5 mg. and both diabase samples, i a and i b , contained 2 mg. of foreign material. After the final weighing of the mixed chlorides, one of each of the duplicates was dissolved in hydrochloric acid and run through the regular procedure for the detection of iron, aluminum, titanium, calcium, and magnesium. None of these elements v a s found in any of the four samples. The other duplicates were used for the determination of potassium with chloroplatinic acid, and then sodium by the difference from the weight of the mixed chlorides. The potassium was separated from the sodium by precipitation as potassium chloroplatinate, the chloroplatinate reduced with magnesium ribbon to metallic platinum, and n-eighed as such (6). Fluorine itself does not interfere with the adsorption and elution of the alkalies. However, the fluorine must be removed to prevent the contamination of the sample by the addition of alkalies from hydrofluoric acid acting on the glassware, and to break up the
aluminum, iron, and titanium fluoride complexes. To volatilize the fluorine completely, the solution must be fumed twice with sulfuric acid (6). Because the final acidity must be controlled so carefully, and because the salts are more readily soluble in hydrochloric acid, it is easier to continue the second fuming with sulfuric to dryness and then add the necessary amount of hydrochloric acid. The total amount of acid added is the quantity that must be considered. Too acid a solution cannot be neutralized because the ions introduced into the solution have in general the same effect as the hydrogen ions. The only change would be the dilution effect of the increased volume from the milliliters of basic solution added ( I O ) . The effect of the elution on iron, aluminum, titanium, calcium, and magnesium was studied individually: 7 meq. of iron, aluminum, and calcium were retained on the column; more than 3.5 meq. of magnesium and 1.9 meq. of titanium &-erenot retained. Perchloric acid could be used instead of sulfuric for the decomposition of the sample. Nore than one evaporation with perchloric acid is also necessary to expel all the fluorine. and sulfuric acid has the advantage of precipitating any lead or barium in the sample. However, Marvin and Koolaver (9) baked the perchlorates at 550” C. and obtained an aqueous solution containing only alkali and calcium salt.. LITERATURE CITED
ll’i Beukenkamo. John. Rieman. William, ANAL. CHEM.22; 582 (1950). (2) Buser, W., Helv. Chim. Acta 34, 1635 (1951). (3) Cohn, W. C., Kohn, H. IT., J . Am. Chem. SOC.70, 1986 (1948). 14’1 Fairbairn. H. W..et al.. E‘. S. Geol. Survey Bull. 980 (1951). ’ ( 5 ) Hillebrand, W. F., Lundell, G. E. F., Bright, H. -4., Hoffman, J. I., iipplied Inorganic Analysis,” 2nd ed., Riley, Ne%- York, 1953. (6) Kayas, Georges, Compt. rend. 228, 1002 (1949). (7) Kayas, Georges, J . chim. phys. 47, 508 _ _ - :1950).
