Benedict, S. R., Theis, R. C., Ibzd., (2) Bene( 61, 63 (1924). (3) h e llll, M. V., Zbid., 97, lvi (1923). (4) Clayton, M. M., .4dams, P. A, Mahoney, G. B., Randall, S. W., Schwarta, E. T., Clin. Clzn. Chem. 6 , 426 (1959). (5j Fisl;, C. H., SubbaRow, Y., J . Riol. Chem. 66, 375 (1925). ( 6 ) Griswold, B. L., Humoller, F. L., McIntyre, A. R., ANAL.CHEM:23, 192 (1951). (7) Hawk, P. B., Oser, T3. L., Summerson,
W. H., “Practical Physiological Chem-
istry,” 13th ed., McGraw-Hill, New York, 1954. (8) Horecker, B. L., Ma, T. S.,Hass, E.,
J. Bid. Chem. 136. 775 (1940). (9) LeBreton, I. W.,’Hall,‘R. J:, Bzochem. J . 67, 400 (1957). (10) McDonald, I. W.! Hall, R. J., Ibzd., 67, 400 (1957). (11) .!atelson, S.,“Microtechniques of Clinical Ckmistry for the Routine
Laboratorv. Charles C Thomas. Springfield,’Ill., 1958. (12) Shin, Y. S., Lee, J. C., Clin. Chem., In press.
Tourtellotte, W. W.,’I-srider, A . J., Slrrentny, B. rl., DeJong, R. S . , J . L a b . Clin. Med. 52, 481 (1958). (14) Zilversmit, D. B., Davis, A. K., (la)
Ibid., 35, 155 (1950).
Y U N GS.SHIS’ Department of Biochemistry St. .4nthony Hospital Terre Haute, Ind. Present address, Biochemistry Laboratory, St. Mary’s Mercy Hospital, Gary, Ind.
Volumetric Determination of Aluminum in Steels, High Temperature Alloys, and Nonferrous Alloys SIR: Investigation of the acidimetric determination of aluminum using potassium fluoride as in Viebock and Brecher’s method (S), and subsequent modifications (1, 6, 4, 6) revealed that the method was effective for the determination of aluminum in ores. Adaptation for its use in metal samples seemed practical. Following the method outlined here, aluminum can be determined in high temperature alloy, bronze, and steel in less thaa one hour. Aluminum is initially separated from its base metal and alloying constituents by mercury cathode electrolysis. Since Ti, V, and Zr are not separated by electrolysis, their effect on the recovery of aluminum was investigated (Table I). W, Tal and Nb are hydrolyzed on fuming with perchloric acid, and are filtered off. NH3+ interferes because of the buffering action of the solution. The concentration of KF is not critical as long as a twofold excess is maintained. p H 8.2 was found to give maximum deflection of the p H meter as well as faster reaction rate of K F with the aluminum. Apparatus. p H meter, standardized with p H 7.0 buffer. Mercury cathode cell.
Reagents. Standard HCl solution, 0.2N t o 0.3N. Ascorbic acid. Standard sodium or lithium hydroxide, 0.2N to 0.3N, standardized for equivalent consumption of the 0.2 to 0.3N HCl. Sodium gluconate, 30% water solution, C.P. grade obtained from Pfanstiehl Laboratories, Waukegan, Ill. Thymol, phenyl mercuric acetate, or mercury (0.1 gram per liter) may be added as B preservative. Potassium fluoride solution, 30% water solution stored in polyethylene and adjusted to p H 8.2 before each use. Sodium or lithium hydroxide, approximately 2N water solution. Phenolphthalein, 1% methanol solution. GENERAL PROCEDURE
Acid-Soluble Aluminum. Dissolve a l,.O-gram sample in 20 ml. of aqua regia. When solution is complete, add 12 ml. of HClOl and bring to fumes. (If chromium is present, it may be advantageous to volatilize it with HCl to cut down electrolysis time.) After fuming, wash the flask with 25 ml. of HzO and heat t o dissolve salts. Filter off any insoluble and hydrolyzed material. (Reserve the residue.) Transfer to a mercury cathode cell with water, making the final volume approximately 100 ml. Electrolyze a t 15 amperes for 20 t o 30 minutes. Check
for completeness of electrolysis with spot tests for iron and nickel. Upon completion of electrolysis, transfer the solution from the cell into a 1liter beaker and make up to approximately 500 ml. with water. Add 40 to 50 ml. of 30% sodium gluconate and approximately 0.1 gram of ascorbic acid to complex and reduce traces of Fe and Mn that are not removed by electrolysis. Add 10 drops of phenolphthalein indicator and make a rough neutralization to a red color with approximately 2.ON LiOH or NaOH. Then with the p H meter in place, adjust the p H back to exactly 8.2 with ”21. Add 35 ml. of 30y0 KF, previously adjusted to p H 8.2, and stir for 1 to 2 minutes. Titrate with standard HC1 until p H is 8.2. Record consumption. Test the final end point with an additional 10 ml. of 30y0 KF. If a deflection occurs, not enough K F was added initially, and the sample should be started again. Total Aluminum. Proceed as for acid-soluble aluminum and ignite the reserved residue in a platinum crucible. Fuse the oxides with sodium carbonate and dissolve in 50 ml. of 10% HC104. Evaporate the solution to strong fumes of perchloric acid. Dilute with water, heat to dissolve salts, and filter. Combine filtrates and proceed as described above for acid-soluble aluminum. DISCUSSION
The basic reaction involved is: Al(0H)s 6KF + K3.41Fs 3KOH
+
Table 1.
Effect of Elements Not Separated by Electrolysis
Amt. Element Titanium
Used, Mg.
Aluminum, Mg. Taken Found
Bias, Mg.
50 25
67.5 67.5
67.0 67.2
-0.5 -0.3
Vanadium
50 25
67.5 67.5
67.5 67.5
0 0
Zirconium
50 30 20 10
67.5 67.5 67.5 67.6
71 . O 69.6 68.9 68.2
+3.5 +2.1 +1.4 $0.7
1166
ANALYTICAL CHEMISTRY
% Recovered 99.26 99.56 100 100 105.19 103.11 102.07 101.04
+
The reaction is not stoichiometric when a direct titration is employed; 2.9 instead of 3.0 moles of hydroxide are released per mole of aluminum. The reaction is stoichiometric, however, if the titration is carried past p H 8.2 with the standard acid, then backtitrated with the standard base and its equivalent amount of acid is deducted from the net titration. However, since the mole ratio of 1 to 2.9 is achieved constantly when titrating directly to p H 8.2, it is not necessary to introduce the overtitration step simply to obtain
stoichiometry. Consistent application is all that is necessary to both the standard samples and the unknowns.
Table 11.
Analysis of National Bureau of Standards Samples
Certified
Sample
Alloy 106.4" Cr, 510,A1 steel 162A Cupro-Si 164A Al-bronze 349 waspaloy 416A Kitralloy G 1189 Nimonic BOA 1191 Waspaloy 1192 W aspaloy Acid-soluble aluminum only.
Value,
NO.
RESULTS
The results of the analyses of eight Xational Bureau of Standard samples are listed in Table 11. The reported values represent an average of five determinations for each standard. The average standard deviation is 0.010 within the concentration range investigated. The method is a t present used in our laboratory for the control determination of aluminum in cobaltand nickel-base alloys. ACKNOWLEDGMENT
4
the procedure. The permission of Sierra Metals Corp., Division of Martin Marietta Corp., to publish this paper is gratefully acknowledqed.
AV.
(5
%
Detns.), yo
Std. Dev.
1.os 0.50 9.59 1.23 1 .os 1.21 1.55 1.07
1 .os 0.492 9.61 1.24 1.08 1.20 1.55 1 .OS
0,0023 0.0107 0.0283 0.0105 0.0016 0.015 0.0016 0.0112
(3) Viebock,
F., Brecher,
c.,
Arch.
'14 (1932). (4) W-atts, H. L., ANAL. CHEM.30, 967 (1~~~8). (5) Watts, 13. L., Ctley, D. W., Ibid., 2 8 , 1731 (1956). 2709
LITERATURE CITED
The author is grateful to W. A. Fahlbusch and H. L. Watts for helpful criticism and assistance in evaluating
(1) Hale, M. S . ,IND.ENG.CHEU.,ANAL. ED. 18, 568 (1946). (2) Snyder, L. J., Ibid., 17, 37 (1945).
GEORGEA. BORUN
Sierra Metals Corp. Wheeling, 111.
Determination of Nitrogen in Nitrocellulose by Infra red Spectrometry SIR: Nitrogen in nitrocellulose is usually determined by the du Pont nitrometer method (9) or by titration (10,If). The nitrometer method is accurate but the working time required per sample is considerable, and the expense and hazard of using the large amount of mercury are objectionable. The titration methods are less timeconsuming than the nitrometer method, but they are not quite as accurate and preparation and standardization of reagents are required. One of the most satisfactory of the titration methods is that of Pierson and Julian (If). The only investigator to report on the determination of nitrogen in nitrocellulose by infrared spectrometry was Kuhn (8) who worked with nitrocellulose films obtained by evaporating ethyl acetate solutions of nitrocellulose. He found that nitrogen could not be determined by measuring the absorbance a t the nitrate band a t 6.0 microns because the fdm showed almost complete absorption at that wavelength. He suggested that the determination could be performed by measuring the ratio of the hydroxyl band a t 3 microns to the carbon-hydrogen band a t 3.5 microns. Rosenberger and Shoemaker (IS) determined nitrocellulose in mixtures of cellulose resins by dissolving in acetone and measuring the absorbance a t the nitrate band a t 11.9 microns. This laboratory developed an infrared method for the determination of nitrogen in nitrocellulose by dissolution in
tetrahydrofuran and measurement of the absorbance a t the nitrate band at 6.0 microns. PROCEDURE
Rinse a 125-ml. Erlenmeyer flask (with a ground glass stopper) with acetone, dry a t 130' C., allow to cool for a half hour or more, and weigh to the nearest milligram. Place 0.31 to 0.32 gram of the sample, previously dried at 65' C. a t 2 to 5 cm. pressure for 4 hours, into an aluminum scoop-type balance pan, and weigh to the nearest 0.1 mg. Pour the sample into the flask, tap the pan, weigh again to the nearest 0.1 mg., and calculate the weight of the sample by difference. Add 45 ml. of high purity tetrahydrofuran using a 50-ml. tall type graduate; do not add the solvent around the sides of the flask as this will cause volatilization losses. Cover and allow to stand overnight in the room (constant temperature) containing the infrared instrument. Swirl the flask and weigh to the nearest milligram. Using a 1-cc. syringe pipet, rinse a 0.2-mm. cell once with tetrahydrofuran and three times with the solution of the sample, then fill it with the solution of the sample. Run the infrared spectrum from 5.80 to 6.05 microns, using the following settings on the Perkin-Elmer Model 21 spectrophotometer: resolution, 941; speed, 1; gain, 5; response, 2; suppression, 0; approximately 0.5 micron per minute. Calculate log ( I A / ~(Figure ) l), and convert this reading to milligrams of nitrogen per gram of solution by con-
sulting the calibration curve. Calculate the per cent nitrogen as follows: mg. of N per gram of solution x grams of solution %N in NC = grams of NC x 10
For the preparation of the calibration curve carry three or more samples of nitrocellulose of known nitrogen content through the procedure, calculate the nitrogen concentration (milligrams of nitrogen per gram of solution), and plot log ( I A / I ) against concentration, using regular graph paper. RESULTS AND DISCUSSION
The most feasible method for determining nitrogen in nitrocellulose by infrared spectrometry was to dissolve the sample in a solvent and to measure the absorbance a t one of the three strong bands due to the nitrate group. These bands occur a t 6.0, 7.8, and 11.9 microns (7,8, l a ) . For the proposed procedure the solvent had to show small absorbance a t the nitrate band and also dissolve nitrocellulose of high and low nitrogen content. Of the solvents that have been used for dissolving nitrocellulose [esters, acetone, methyl ethyl ketone, cyclohexanone, dioxane, methanol, nitrobenzene, nitroethane, tetrahydrofuran (3, 4), propylene oxide, pyridine, and a mixture of ethyl alcohol and ether] only acetone and tetrahydrofuran merited consideration for the problem a t hand. Some work was done on the use of VOL. 34, NO. 9, AUGUST 1962
1167
