to the reduction of the carbonyl, as shown in Equation 2. -bH
- L H
I
C=O
I
+ 2e + 2 H f +
i:I =O + H20
ACKNOWLEDGMENT
The authors are grateful to Beatrice S. Gallagher, Sloan-Kettering Institute for Cancer Research, for the 16-hydroxy- (or acetoxy)-17-ketosteroids used in this investigation.
(2)
Proof of the structure of the products of large scale reductions will be published (3).
LITERATURE CITED
(1) Barnett, J., Morris, C. J. 0. R., Biochem. J . 40, 450 (1946). ( 2 ) Kabasakalian, P., McGlotten, J., J. Electrochem. Soc. 105,261 (1958). (3) Kabasakalian, P., RIcGlotten, J.,
Yudis, AI. D., J . Am. Chem. SOC. in press. (4) Neiman, &I. B., Markina, Z. V.,
Zavodskaya Lab. 13, 1174 (1947). (5) Prelog, V., Hafliger, O., Helc. Chim. Acta 32, 2088 (1949). (6) Stackelberg, 31. von, Stracke, W., 2. Elektrochem. 53, 118 (1949). (7) Winkel, A., Proske, G., Ber. 69, 1917 (1936). (8) Wolfe, J. K., Hershberg, E. B., Fieser, L. F., J. Biol. Chem. 136, 653 (1940).
RECEIVED for review September 9, 1958. Accepted December 3, 1958.
Coprecipitation of Sodium in Sulfate Determination A Spectrographic Method JOHN
L.
VOTH
Deparfment of Chemistry, University of California, Davis, Calif.
FSpectrographic analysis of sodium offers a new approach to an old problem. In the sulfate precipitation by barium chloride, the coprecipitation of sodium doubles, only, with a 20-fold increase in sodium chloride concentration. Sudden addition of barium chloride solution decreases coprecipitation by half. Coprecipitation reaches a constant value after 6 hours' hot digestion of the precipitate and remains the same over a pH range from 2 to 6. Results indicate that sodium coprecipitation is not so great as reported.
E
in the precipitation of sulfate by barium chloride solution has been attributed to sodium sulfate occlusion (1, 3-5). The spectrograph simplifies the determination of sodium because no further sample preparation is required after precipitation and ashing. 15-aldbauer and Gantz (6) have reported the coprecipitation of ions other than sodium n-here spectrographic techniques Tere used. Allen and Johnston (1) and Johnston and Adams (4) determined the sodium occlusion in barium sulfate precipitation by redissolving the precipitate in concentrated sulfuric acid and reprecipitating by dilution in water. The filtrate was evaporated to dryness and the residue weighed as sodium sulfate. RROR
Reagent grade chemicals were used without further purification. Preliminary spectrographic examination of a barium sulfate precipitate indicated no cations other than barium and sodium. The method of precipitation of Allen and Johnston (1) was closely followed for a comparison of results. The volume of sodium sulfate solution TT as 350 ml., p H 1094 *
ANALYTICAL CHEMISTRY
of precipitation approximately 2, and the weight of the precipitate was 2 grams. The barium chloride solution, aged at least 24 hours (S),was added from a buret with a capillary tip so attached that 21 ml., a slight excess, would be delivered in 4 minutes. Digestion time on the steam bath was 18 hours. The precipitate was filtered through 11-cm. KO.42 Whatman paper. After transfer of the precipitate to the filter paper, it was washed ten times with hot water made acid to methyl orange and then five times with hot water only. The last washing was tested with a 5% silver nitrate solution and to ensure that it had been adequate, two precipitates were further washed with 25 ml. of hot water and the water was tested for sodium ion by flame photometry. Less than 0.3 p.p.m. of sodium, an amount insufficient to affect the results, was present. SPECTROGRAPHY
The precipitates, after ignition, were prepared for spectrochemical analysis by mixing with a buffer composed of one half graphite (National Carbon Co. SP2 grade), one quarter lithium sulfate, and one quarter aluminum sulfate. Equal parts of buffer and barium sulfate were weighed and mixed for 40 seconds on a Wig-L-Bug (Spex Industries, Inc.). Standard samples of the same composition were prepared n-ith reagent grade barium sulfate free of sodium. Sodium sulfate was added to give three samples containing 0.16, 0.064, and 0.025% of sodium, respectively. Triplicate arcings were made on each spectrographic plate of the three samples. The sample electrodes 7.9 mm. in diameter had a cup 4.8 mm. in diameter and 4 mm. deep. A hole was drilled in the bottom of the cup, 1.5 mm. in
I
01
02
I
I
l l l l l l
05
I
I .2
PER CENT
Fiaure 1.
N i 3303.0 Ba 2702.6
Ratio of intensities vs. per cent sodium
diameter, and 8 mm. deep, measured from the bottom of the cup. Twenty milligrams was weighed on filter paper, transferred to the cup, and tamped into the hole a t the bottom with the b u t t end of a 1.5-mm. drill. The cup was then cut away with a lathe, exposing the sample to the arc. The counterelectrode was 1/4-inch rod, 1 inch long with a post cut a t one end 2 mm. in diameter, and 11 mm. long. A direct current arc of 140 volts, 12 amperes, was used with the sample located in the anode. Exposure time \vas 1 minute. A. rotating sector placed before the slit reduced light intensity 507,. An arc gap of 3 mm. was maintained a t a constant position by reference to a magnified image of the arc projected on a screen. The spectrograph was a large Littrow (Bausch RLomb Optical Co.) with quartz prism, photographing the region 2500 to 3500 A. on SA-1 plates (Eastman Kodak Co.). The characteristic curve of the spectroscopic plates was determined from selected lines (2) of the iron arc. The analytical curve was obtained by plot-
K a 3303.0 Ba 2702.6’ against the concentration of sodium on log-log paper (Figure 1). 4 background correction was made for the sodium line. All experimental samples were arced in triplicate. The reproducibility of the combined chemical and spectrographic analyses was determined b y check samples which indicated that the results rrere accurate for sodium to within 20% of the reported value. Figure 1 is a typical plot of the standard curve. For determination of sodium in the barium sulfate, the values obtained from the plot were multiplied by 2 because samples were diluted one half with buffer. Experimental conditions were changed to determine their effect on sodium coprecipitation. ting the ratio of intensities,
PROCEDURE
Effect of Sodium Chloride Concentration. Sodium chloride was added
t o t h e sodium sulfate solution before precipitating t h e sulfate with barium chloride solution. T h e increase in sodium coprecipitation with increase in sodium chloride concentration ivas small (Table I). The method of Johnston and coworkers (1. d ) for recovery of sodium sulfate from the barium sulfate precipitate TT as used in one instance. The barium sulfate precipitate originated from the solution containing 100 grams of sodium chloride. The recovered material weighed 13.6 nig. Spcctrographic examination indicated this was principally sodium su1f:tte. Calculated as sodium sulfate this Sives a value of 0.217, sodium, in good agreement with the spectrographic result of 0.24% (Table I). The discrepancy between these results and those of Johnston and ildams (4) remains unexplained.
Table I. Sodium Coprecipitation with Change in Sodium Chloride Concentration
Sodium Chloride Added to Solution, Grams 0 5 10 20 30 50 70 100
Sodium in Barium Sulfate, yo Spectro- Johnston and graphic Adams ( 4 ) 0.09 0.13 0.16 0.14 0.14 0.18 0.21 0.24
0.13 0.28 0.31 0.40 0.51 0.64 0.77 0.74
Effect of Concentration of Barium Chloride Solution. Rate of Addition.
Each solution contained 45 grams of sodium chloride. Changing t h e barium chloride concentration from 5 t o 10% had no effect on coprecipitation of sodium. Sudden addition of bariuni chloride solution decreases coprecipitation t o half. Effect of Concentration of Sodium Sulfate Solution. T h e sodium sulfate concentration was varied so t h a t barium sulfate precipitates were obtained increasing in rreight b y 0.5 gram from 0.5 t o 3 grams. T h e barium chloride concentration was changed for each solution so t h a t 50 ml. would precipit a t e all of t h e sulfate with a slight excess of barium chloride. Time of addition was 2.5 minutes. KO significant difference in sodium coprecipitation was observed. Time of Digestion. Each solution contained 45 grams of sodium chloride. Table I1 compares t h e results with those of Johnston and Adams (4) , whose solutions contained 5 grams of sodium chloride.
Table II. Change of Sodium Coprecipitation with Time of Digestion
Time of Digestion, Hr. 0 0 0.25 2 3 6 18 20 33 48
Sodium, % Johnston Spectroand graphic Adams ( 4 ) 0 72 0 50 0 37
0 37 0.24
0.16
0 22 0 14
o.i5 0.17
pH of Solution. T h e p H was varied from 2 t o 6 ; t h e other experimental conditions were unchanged. S o significant difference in sodium coprecipitation was observed. Fischer and Rhinehammer (5) noted a decrease in n-eight of barium sulfate with decrease in p H and attributed it to coprecipitation of sodium sulfate. However, these results indicate this decrcase is not due to such coprecipitation. LITERATURE CITED
(1) Allen, E. T., Johnston, John, J . Znd. Eng. Chem. 2 , 196 (1910). 121 Crossn-hite, H. AI., Spectrochim. Acta ’ 4, 122 (1951). (3) Fischer, R. B., Rhinehammer, T. B., .&XAL. CHEM.2 5 , 1544 (1953). (4) Johnston, John, .&dams, I. H., J . Ana. Chem. SOC.33, 829 (1911). (5) Riemann, W. H., Hagen, George, IS-D.ENG.CHEN.. ANAL. ED. 14. 150 (1942). (6) Wddbauer, Louis, Gantq E. S., Zbid., 5 , 311 (1933).
RECEIVED for review April 4, 1958. Accepted January 12, 1959.
Controlled-Potential Coulometric Determination of Europium W. D. SHULTS Anolytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
b The europium content of europium oxide can b e precisely determined by controlled-potential coulometry. The electrolytic reduction of europic ions was not satisfactory for direct quantitative titration but was for the preparation of europous ions. Immediate coulometric reoxidation of the europous ions thus produced is the means of quantitative estimation. The method is reasonably rapid and is free from
interference from the usual contaminants.
T
thermal neutron absorption cross section of europium is very large. This, plus the fact that the products of neutron capture by europium possess even larger cross sections, makes i t particularly useful as a reactor control rod material ( 2 ) . A precise method HE
for its determination is needed to estimate the exact europium content of commercially available or purified europium oxide. The estimation of europium has not received much attention. Redox titration (IO),in which europic ions are reduced to europous by passage through a Jones reductor and then titrated with standard oxidant, is satisfactory for gram quantities of europium, b u t is VOL. 31, NO. 6, JUNE 1959
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