r
I
Table IV.
Food product Cereal pellets Dried raisins (KO. 1 ) Dried raisins (No. 2) Flour (No. 1 ) Flour (No. 2)
m
m 0
* 0 W
w E
e
Reproducibility of Entire Procedure
Moisture (yo) Proposed GLC procedure Other 21.5, 21.7, 21.3, and 21.5 18.7, infrared balance 9 . 2 , 9 . 2 , and 9 . 3 7 . 1 , Vat. oven ( 6 hr.) 11.3, Vac. oven ( 6 hr.) 13.6, 13.8, and 13.8 12.6, 12.5, 12.6, and 12.6 12.5, Air oven 130' C. 13.5, Air oven 130' C. 13.5, 13.7, and 13.6
0
W
a
Figure 1 , Typical gas chromatogram of the methanol extract of a food product 1. 2. 3.
Methanol sec-Butyl alcohol Water
from the clear filtrate. The GLC analysis takes about 5 minutes. Calculations. T h e ratio of peak height of water t o peak height of .set-butanol ( R H ) is calculated from t h e d a t a on t h e chromatogram and converted t o the weight ratio of water t o sec-butanol (Rw)by using a cali-
bration curve prepared from data such as that included in Table 11. R w is multiplied by milliliters of sec-butanol to get milliliters of water and this in turn can be converted to per cent moisture in the original sample. DISCUSSION
The reproducibility of the GLC portion of this procedure was checked by preparing two mixtures of water, sec-butanol, and methanol equivalent to a mixture which would be obtained from 15-gram samples of food containing 25% and 30% moisture, respectively. The Rx values so obtained are tabulated in Table 111. A typical chromatogram is illustrated in Figure 1.
The reproducibility of the entire method is illustrated in Table IV. This method has been for routine quality control work for Over a year. The column is very stable if not heated above 130" C. We have used one column continuously for a year with little change in resolution. LITERATURE CITED
(1) Carlstrom, A. A., S encer, C. F., Johnson, J. F., ANAL.&EM. 32, 1056 (1960). (2) Stein, H. H., Ambrose, J. M., Ibid., 35, 550-2 (1963).
WARRENM. SCHWECKE JOHN H. KELSON Quality Control Department General Mills, Inc. Minneapolis, Minn.
Separation of Certain Cations from Mixtures of Various Cations on Ion-Exchange Papers-Arsenic, Barium, Cadmium, Tin, and Zinc SIR: Previous reports in this series have demonstrated the separation of silver or thallium ( 1 ) and arsenic or antimony (2) from virtually all other ions by development with complexing reagents on ion-exchange resin loaded filter papers. Exactly the same techniques and procedures have now been employed to test various other selective reagents (all in aqueous solution) for such separations. Exploratory tests were performed by developing the following 26 ions individually: Ag, T1, Pb, Cd, Cu, Co, Xi, Hg(I), Hg(II), As(III), Fe(III), Sb(III), V(V), Bi, Sn(IV), Au(III), Pt(IV), Al, Ce(III), Ce(IV), Mg, Zn, Ba, Mn(II), Cr(III), and U(V1). Test solutions (0.050M) were prepared by dissolving the reagent-grade nitrate, chloride, sulfate, or acetate in water. Mercury(1) nitrate was stabilized with 48 ml. of HNO, per liter of solution. Platinum(1V) and gold(II1) were prepared as the usual chloro complexes. T o dissolve uranium(V1) acetate, the minimum necessary amount of glacial acetic acid was added. Vanadium(V) was a saturated solution of VSOS in 0.10M sulfuric acid. Antimony(III), tin(IV), and arsenic(II1) chloride solutions were stabilized with 6M HCl. 690
0
ANALYTICAL CHEMISTRY
Bismuth chloride was dissolved in 1:5 HCl. To dissolve cerium(1V) sulfate, the minimum necessary amount of sulfuric acid was added. The promising reagents were then tested with a mixture containing 15 compatible, representative ions, including the ion t o be separated. One such mixture contained Ag, -41, Ba, Cd, Ce (IV), Cr, Co, Cu, Fe, Pb, Mg, Mn, Ni, T1, and Zn. Four spray reagents, previously described ( 1 , 2, 4)served for the detection of all the ions listed above. The reagents tested were the same ones which were used as background electrolytes in earlier electrochromatographic studies of the ions (3, 4). We therefore know the sign of the charge of each ion in each developing solution. The results given below are based upon at least four migrations of each ion in each system, with stated RFvalues having a standard deviation of +0.04 or less, Migration distances were generally 30 t o 35 cm., which took about 2 hours with the cation-exchange paper and 75 minutes with the anion-exchange paper. Arsenic and barium were separated from the 24 other ions and from each other by development with a solution of 0.0125M EDTA and 0.05M ammonia,
p H 9.2, on filter paper loaded with strongly basic anion-exchange resin in the (ethylenedinitri1o)tetraacetate form (Reeve Angel Grade SB-2, control -4-10297). Both arsenic and barium were complexed to form anionic species in this system. Arsenic had RF 0.78 and was separated by 2 cm. from the closest zone (Bi, RP0.58). Barium had RF = 0.89 and was separated by 3 cm. from the arsenic zone. The vanadium zone could not be detected in this system, so its position is indeterminate. Arsenic and cadmium were separated from the 24 other ions and from each other by development with a solution of 0.5031 sodium chloride, p H 6.5, on filter paper loaded with strongly acidic cationexchange resin in the sodium form (Reeve Angel Grade SA-2, control A-7802-1,2). Both arsenic and cadmium were cationic in this system. Cadmium had RF 0.46 and was separated by 3 cm. from the closest zone, vanadium, which trailed back to the origin. -4rsenic had RF 0.91 and was separated by about 10 cm. from the cadmium zone. Arsenic was separated from the 25 other ions, and tin was separated from all except antimonous, vanadium, mercuric, and cadmium ions by development
with a solution of 0.50M hydrochloric acid, pH 0.30, on the SA-2 paper in the hydrogen form. Both arsenic and tin were cationic in this sistem. Tin and arsenic had RP values '3f 0.40 and 0.91, respectively, and were separated by 20 cm. Arsenic was separated from the 25 other ions, and zinc was separated from all except vanadium ions by development with a solution of 0.50M sodium hydroxide, pH 14, on the SA-2 paper in
the sodium form. Both arsenic and zinc were anions in this system. Zinc and arsenic had RF values of 0.57 and 0.85, respectively, and were separated by about 10 cm. Except for the vanadium, the closest zone to the zinc is gold, which streaks from the origin to within 2 cm. LITERATURE CITED
(1) Sherma, J., Tahnta 9 , 775 (1962). (2) Sherma, J., Cline, C. W., Ibid., 10, 787 (1963). (3) Sherma, J., Evans, G. H., Frame,
H. D. Jr., Strain, H. H.. ANAL.CHEM. 35. 224 ~~- flR6.7). I
\ - - - - ,
(4) Strain, H. H., Binder, J. F., Evans, G. H., Frame, H. D., Jr., Hines, J. J., Ibid., 33. 527 (1961). I
.
JOSEPH SHERMA Lafayette College Easton, Pa. WORKsupported by a Summer Research Grant from Lafagette College. The electrochromatographic studies were performed at Argonne Sational Laboratory where the author was a Resident Research Associate during the summers of 1961 and 1962 in the laboratory of H. H. Strain.
Indirect Volumetric Determination of Cobalt in Ferrous Alloys with EDTA as Indicated by Eriochrorne Black T SIR: The method of analysis for large amounts of cobalt in steel as reported by Lewis and Straul, ( 2 ) has been modified for use with Ekiochrome Black T to indicate the end point of the titration. Although Eriochrome Black T was reported by Relclier (3) as giving less satisfactory end points than other indicators, careful control of the titration variables resulted in accurate and precise recoveries of milligram amounts of cobalt from various 1 ypes of steel.
Table 1. Effect of Variables in Titrating Cobalt with EDTA (Eriochrome Black T)
Variable Time elapse during titration, seconds
Cobalt recoveredo,
75 .I
135 270 300 360
mg.
20.24 20,39 20.09 20.09
Temperature at start of titration, "C. 6 10 20 30 40 50
20.24 20.54 19.94 20.39 20.09 20.09
The procedure used was similar to that of Lewis and Straub. However, some deviations are to be noted. Nitric acid was removed by baking the sample in perchloric acid rather than in hydrochloric acid. This approach lends itself readily to simple removal of chromium as chromyl chloride with gaseous hydrogen chloride. After chromium has been volatilized, the sample is fumed intensely in perchloric acid, cooled, and diluted with water. A filtering step then removes the hydrolyzable elements such as niobium, tantalum, and tungsten. This step has two advantages. Quantitative removal of these undesirable acid-insolubles simplifies cleaning of the resin so that it may be used for numerous analyses before discarding. Also, if these elements are not present in the resin, the chance of possible hydrolysis (1) during subsequent elution with weaker hydrochloric acid is avoided. That this hydrolysis does occur is evidenced by precipitates in the eluants and abnormally high recoveries. Among the indicators evaluated for possible use in the direct or indirect titration of cobalt with EDTA were murexide, pyrocatechol violet, pyrogallol red, and brompyrogallol red. Indefinite end points or low levels of cobalt tolerance ruled them out for use for milligram amounts of cobalt. Welcher
indicated that Eriochrome Black T had been used to titrate from 15 to 50 mg. of cobalt but with an unsatisfactory end point. Investigation of the titration conditions-pH, temperature, volume of solution, reducing agent, and time elapse from addition of indicator to finish-showed that the following conditions as chosen for this modified procedure result in accurate and precise cobalt recoveries (Table I). With proper care and no delays, titrations can be conducted in about two minutes; under most laboratory conditions, normal room temperature and addition of reagents a t the proper volume will provide a solution temperature of about 30' C. Best results with the reagents used are obtained in a total volume of about 200 ml.; the addition of 10 ml. of pH 10 buffer solution (60 grams of ammonium chloride and 5iO ml. of ammonium hydroxide diluted to 1 liter) will provide the optimum hydrogen ion concentration for this indicator. Xddition of about 0.5 gram of hydroxylamine hydrochloride to the solution to be titrated will retard atmospheric oyidation of the indicator. Table I1 is a compilation of some of the results obtained using the recommended procedure. Table I11 shows the types of alloys analyzed and their nominal compositions. As can be seen
Total volume at start of titration, ml. 250 250 200 200 150 100
19.97 20.24 20.39 20.39 20.24 20.09
PH 6.6 7.4 8.1 9.0 10.0 a
20.40 mg. of cobalt taken.
19.97 19.82 20.12 20.35 20.39
Table 11.
Volumetric Cobalt Recoveries KO.
Sample NBS 153a
NBS 167 NBS 168 NBS 349 NBS 1187 No. 524 No. 1 No. 2 No. 3 No. 4 No. 5
Certificate
Experimental av.
8.47 42.90 41.20 13,95 20.80
8.44 42.85 41.28 13.91 20.82 17.11 14.86 15.70 17.79 18.63 16.85
...
... ...
...
...
...
2u
of
determinations
f0.07 10.20 f 0 .20 f 0 . 06 k0.14 3 Z O . 07 f 0 .04 f O .10 f0.07 3Z0.08 f 0 . 08
4 5 4 12 5 4 5 5 5
VOL. 36, NO. 3, MARCH 1964
a
5 5
691
