1826
ANALYTICAL CHEMISTRY
Early work indicated that unless careful washing of the filter paper was done, a significant amount of biphenyl was lost. Comment should be made on the analysis range of 0 2 t o 0.7% biphenyl by weight that was used. This range can be increascd sommvhat above 0 7y0,but is limited by the tendency of the standard curve to flatten out a t higher concentrations. Below 0.2% it becomes difficult to measure the absorption peak accurately. Before developing this method investigation showed no interference a t this absorption peak from thc ot,her constituents present in Phenodor X, or in the fiberboard of the cartons. This was shown by recording the absorption curves from 13.90 t o 14.60 microns of pure carbon tetrachloride, Phenodor X minus biphenyl in carbon tetrachloride solution, and a carbon tetrachloride extract of untreated fiberboard. Thpse three Curves proved t o be identical (Figure 3). Finally, something should be said concerning the nwthod of calculating results. Since Beer's law holds throughout the range of this analysis, the standard curve can be plotted according to this law. However, in the absence of interfering factors it Jva. found easier and quicker, as vie11 as accurate, to make up standard solutions containing only biphenyl and carbon tetrachloride, and to measure the absorption peak directly in centimeters in the arbitrary fashion illustrated by Figure 1. This is in reality a measure of transmittance except that the level of tangent line A in Figure 1 decreases m-ith increasing biphenyl concentration.
500 0
P
s
=E 4 0 -
.-
c t
30
-
c 0)
2 a 2
o
I I 4 60
Wove L e n g t h
-
-
13 90 Microns
Figure 3. Infrared Chart of Carbon Tetrachloride, Phenodor X Minus Biphenyl in Carbon Tetrachloride Solution, and a Carbon Tetrachloride Extract of Untreated Fiberboard This increases the tendency of the standard curve t o flatten out at higher concentrations of biphenyl. LITERATURE CITED
(1) Steyn, A. P., and Rosselet, F., Analyst, 74, 89-95 (1949). (2) Tomkins, R. G., and Isherwood, F. A., Ibid., 70,330-5 (1945). RECEIVED for review April 21, 1952. Accepted August 8, 1952. Florida Agricultural Experiment Station Journal Series No. 21.
Photometric Determination of Aluminum in Alkalies 0. A. KENYON AND H. A. BEWICK Solvay Process Division, Allied Chemical & Dye Corp., Syracuse, IV. Y .
MALL quantities of aluminum are not easily and
it( curately determined in alkali products by present procedures. The conventional gravimetric technique of determining combined hydrous oxides by difference is tedious and of doubtful a(-curacy for samples containing less than 0.1 % aluminum. The photometric determination of aluminum as aluminum oxinate in chloroform has been reported by rllexander ( I ) , Xoeller ( 5 ) , Gentry and Sherrington (a), and Wiberley and Bassett (6). Homver, there has been some disagreement concerning the proper conditions for the chloroform extraction. Using the procedure outlined by TF'iberley and Bassett (63, a critical study was undertaken to evaluate the factors affecting the recovery of aluminum oxinate. These were pH, digestion period, conditions for extraction and complexation, or removal of interfering ions commonly found in alkali products. By the method described in this paper, 10 to 200 micrograms of aluminum have been satisfactorily recovered from samples containing 200 micrograms of iron, 100 micrograms of copper, 5 micrograms of nickel, and 10 micrograms of mangancsp.
PROCEDURE
Acidify alkali samples with hydrochloric acid to a p H of less than 4. For alkali samples containing silica, pour the alkaline solution of the sample into the acid to avoid precipitation of silica. Transfer a 50-mI. or smaller aliquot of the acidified solution containing 200 micrograms or less of aluminum oxide into a 100ml. beaker. Add 3 ml. of 10% tartaric acid, 2 ml. of ammonium acetate buffer (20% ammonium acetate in 1 N ammonia solution), 2 ml. of oxine reagent (2% 8-quinolinol in 1 N acetic acid solution) and adjust the p H to 6.6 =k 0.2 with ammonium hydroxide. Digest the sample for 15 minutes a t 60' to 70" C. in a water bath and cool. If copper, iron, and nickel are to be removed, adjust the pH t o 2.8 with 1 t o 3 hydrochloric acid, transfer t o a separatory funnel, and extract these oxinates with two 10-ml. portions of chloroform. To the aqueous solution add 1 ml. of oxine reagent and adjust the p H to 6.6 f.0.2 with 1 t o 3 ammonium hydroxide. If manganese is present, the p H should be adjusted to 5.7 instead of
6.6. Digest the sample 15 minutes in a water bath a t 60" t o 70" C. and cool. After the digestion in either case, make up the aqueous volume to 80 ml. and extract the aluminum ovinate with two 10-ml. portions of chloroform, shaking the firit extraction 2 minutes and the second extraction 1 minute. Filter the extracts through filter paper n e t with chloroform to iemove traces of water, and make up t o 50 ml. with chlorofoini. Determine the absorbancy values pith a photometer :it 390 1 1 1 using ~ a I-cm. cell. The beakers in which the oxinate precipitations are made must be rinsed with the chloroform used for the extraction t o remove any oxinates which might otherwise adhere t o the glass. Prepare standard analytical curves folloR-ing the same procedure, using one series of evtractions at pH 6.6. Prepare standards by dilution from a standard aluminum solution [4.45 grams of assayed aluminum ammonium sulfate, 4l8(SO4)3.(NH4),SO,. 24H,O, in 1 liter of solution. One milliliter = 500 micrograms of aluminum oxide]. EXPERIMENTAL
Effect of pH. In the work reported here microgram quantities of aluminum were taken and completely recovered over the range investigated, pH 5.5 to 7.0. Digestion Period. All investigators, with the exception of Merritt and Cady ( 4 ) in their gravimetric determination of larger amounts of aluminum, have given no consideration to the need for a digestion period. After careful study, a digestion period of 15 minutes in a water bath of 60" to 70' C. was found to be necessary for the complete recovery of aluminum (Table I).
Table I.
Effect of Digestion Period at 60" to 70" C.
Aluminum Oxide Taken, y 100 100 100 100 100
Digestion Period, Minutes 0 5 10
Aluminum Oxide Recoifered, y 75.8 95.0 99.3
15
100.0
30
100.0
1827
V O L U M E 2 4 , NO. 11, N O V E M B E R 1 9 5 2 A similar digestion period with additional oxine is also required for the complete recovery of aluminum after the removal of copper, iron, and nickel oxinates by chloroform extraction a t p H 2.8. Concentration of Tartaric Acid. Gentry and Sherrington ( 2 ) stated that the presence of tartrates interfered with the recovery of aluminum. It was desirable in this application to use tartaric acid to complex small quantities of iron. .2 maximum of 0.3 gram of tartaric acid can be tolerated in the 80 nil. of solution prior to the extraction of aluminum without serious loss of aluminum and this quantity of tartaric acid will complex up t o 5.6 micrograms of iron. S o rrror in analysis results when the standard rurve iq prepared in the same manner as samples are analyzed.
Table IT.
100
3
Conditions of Chloroform Extraction
10
10 10
10
2 2
1
1
100
3
aluminum, additional oxine reagent must be added before the second digestion period t o replace losses due t o reagent extraction. Effect of Diverse Ions. The principal constituents in alkali products which would cause interference are iron, copper, nickel, and manganese. By using proper p H adjustments according to information reported by Gentry and Sherrington (3) the iron itnd copper oxinates may be completely extracted with chloroform and the nickel oxinate partially extracted at p H 2.8. After t'he removal of these constituents the aluminum oxinate may be completely recovered a t p H 5.7 without interference from the manganese if this constituent is present. Otherwise, all aluminum extractions were made a t pH 6.6. If the aluminum values to be determined are 25 p.p.ni. of aluminum oxide or higher, usuallJ- the interfering substances in alkalies are small enough to be insignificant and their renioval is unnecessary. Iron will be an iiiterference if, a t the end of the first digestion, the solution is colored greenish black. Reproducibility. Fourteen synthetic samples containing 100 micrograms of aluminum oxide had an arithmetic average of 100.0 micrograms, a maxinium deviation of 0.4 microgram, and a standard deviation of 3 ~ 0 . 2microgram. ACKNOWLEDGMENT
Extraction. Factors considered in the chloroform extraction of aluminum oxinate were: the number of extractions required, the volume of chloroform in each extraction, and the shaking time required for each extraction. From the data in Table 11, it was concluded that the optimum conditions for the complete extraction of aluminum oxinate with chloroform were two 10-ml. portions of chloroform with a 2-minute shaking period for the first extraction and a I-minute shaking period for the second extraction. Where two aeries of extractions are required for the removal of interfering metals and later the determination of
The authors wish to thank G. 1., blurphy and George Oplinger for their assistance. LITERATURE CITED
(1) Alexander, J. IT.,Ph.D. thesis University of Wisconsin. 1941. (2) Gentry, C. H. R.. and Sherrington, L. G.. Analyst, 71, 432 (1946). (3) Ibid., 75, 17 (1950). (4) Merritt, L. L..and Cady, R. T., 11.S thesis, India'na University,
1948. ' 5 ) Moeller, T., ISD. EXG.CHEM., ANAL.ED., 15,346 (1943). (6) Wiberiey, S. E., and Bassett. L. G., A s a ~CHEM., . 21, 609 (1949). RECEIVEDf o r revie%- Soi.eniber 23, 1 9 ~ 1 , Accepted August 15, 1952
Polarographic Studies of Some Organochlorosilanes EARL A. ABRAHAMSON, JR.', AND CHARLES A. REYNOLDS Department of Chemistry, University of Kansas, Lawrence, K a n . RGANOHALOSILANES are particularly important today as intermediates in the field of silicone polymers. However, because of the ease of polymerization of their hydrolysis products, the problem of chemical analysis has been a difficult one, and the analysis has usually consisted of determining the particular organohalosilane in terms of the respective elements present. Since both chloroform and carbon tetrachloride are reducible a t the dropping mercury electrode ( I ) , it was thought that the organohalosilanes might also give polarographic waves which could be used for quantitative estimation of the silanes. An alternative polarographic determination would be possible if the organohalosilane reacted quantitatively with the solvent, producing a substance which was reducible a t the dropping mercury electrode. Since organohalosilanes undergo solvolysis readily in protonated solvents, most of the nonaqueous solvents in which polarographic work has been done wrre eliminated. A solvent had to be chosen in which the silane was soluble without reaction, or with which the silane reacted to give reducible products. Also, enough supporting electrolyte had to be dissolved in the solvent so that a solution of sufficiently low resistance for polarographic work was obtained. In addition, the Polvent itself had t o be nonreducible m-ithin a workable potential span. The solvents which seemed 1
Present address, E. I d u Pont de Kernours 8.z Co., Wilmington. Del.
best to fulfill these three requirements xvere acetone, methyl ethyl ketone, tetrahydrofuran, avetonitrile, formamide, and pyridine. APPARATUS AND REAGENTS
A Sargent Model X X I visible recording polarograph was used for all the work. All values of potential set on the span were checked with an auxiliary potentiometric circuit. Purified methyl ethyl ketone was redistilled and the fraction boiling between 79" and 80" C. was retained. The chloroform used was twice distilled and the fraction boiling between 60' and 62' C. was collected. Analytical grade acetone and for mamide were used without further purification. Analytical grade acetonitrilt~u a s used after drying over phosphorus pentoxide, Tetrahydrofuran was twice distilled, the fraction boiling between 62" and 64" C. being collected and dried over metallic sodium. Analytical grade pyridine was suitable for use after being dried over potassium hydroxide, redistilled, and dried over barium oxide. All the supporting electrolytes used were of analytical grade RESULTS AND DISCUSSION
Direct Reduction of Organochlorosilanes. Although carbonchlorine bonds are knom-n to be reducible a t the dropping mercury electrode, all attempts to reduce the silicon-chlorine bond
