Leisey, F. A., Ibid., 26, 1607 (1954). Mitchell, J., Jr., Ibid., 23, 1069 (1951). Mitchell, J., Jr., Smith, D. M., “Aquametry,” Interscience, Yew York, 1948. Ihid., p. 65. Ibid., p. 137. Ibid., pp. 381, 382.
(12)Peters, E. D., Jungnickel, J. L., ANAL.CHEM.27, 450 (1955). (13)Sneed, R. W., Altman, R. W., Mosteller, J . C., Ibid., 26, 1018 (1954). (14)Tamele, M. W., Ryland, L. B., IND. E K G . CHEbl., -4NAL. ED. 8, 16 (1936).
(15)Wiberley, J. S., ANAL. CHEM.23, 656 (1951).
RECEIVEDfor review June 10, 1957. Accepted February 18, 1958. Group Session on Analytical Research, 22nd Midyear Meeting, Division of Refining, American Petroleum Institute, Philadelphia, Pa., May 1957.
Gravimetric Determination of Bismuth Using Hypophosphorous Acid DONALD R. BOMBERGER’ University of California Radiation laboratory, Livermore, Calif.
b A simple method is provided for gravimetric determination of bismuth in the presence of a number of metallic elements. Bismuth is reduced to the metal by hypophosphorous acid from a perchloric acid solution, dried, and weighed.
I
gravimetric determination of bismuth as a major constituent in alloys or solutions, the choice of methods is limited to oxyhalide, phosphate, and cupferron precipitations. The oxyhalides are satisfactory for small amounts of bismuth only. The phosphate and cupferron methods as described by Silverman and Shideler (3) were satisfactory, but involved considerably more manipulations than precipitation with hypophosphorous acid. Reduction to the metal by formaldehyde (4),glucose ( 2 ) ,and hypophosphorous acid ( 1 ) did not produce quantitative methods. The present Fork showed that bismuth could be reduced to the metal and quantitatively determined using hypophosphorous acid. N THE
REAGENTS A N D PROCEDURES
Bismuth standard was prepared by dissolving reagent grade bismuth nitrate pentahydrate in distilled water, adding sufficient perchloric acid to render the final solution IN, and evaporating to heavy white fumes. The solution was diluted to obtain the desired bismuth concentration and standardized as the phosphate ( 3 ) . Hypophosphorous acid, 30 to 32%, N.F. grade, as supplied by Baker and Adamson. Perchloric acid, 70%, double vacuum distilled as supplied by G. Frederick Smith Chemical Co. Other chemicals were of reagent grade. Prepare sample solutions in IN per1 Present address, Research and Development Division, Pittsburgh Consolidation Coal Co., Library, Pa.
chloric acid free from chloride, nitrate, and sulfate, containing 1 to 2 mg. of bismuth per ml. Add 1 ml. of 30 to 32% h-ypophosphorous acid for each 20 ml. of solution. Heat just below boiling on a hot plate or steam bath for 1 to 2 hours, after which the supernatant becomes clear. Stir several times during digestion to agglomerate precipitate. Pour supernatant immediately, while hot, through a fine sintered-glass filter crucible. Wash twice by decantation with distilled water and transfer sponge with stirring rod and distilled water to crucible. Wash with 95% ethyl alcohol and ethyl ether, and dry a t 110’ C. for 0.5 to 1 hour. Cool in a desiccator and weigh as metallic bismuth.
hot, acid conditions must be avoided. Higher oxidation states of most metals fall into this category. Treatment of the sample solutions in 1N perchloric acid with 6% sulfurous acid, followed by boiling, eliminates the difficulty in most cases. Nitrate and chloride also interfere, even in small amounts. Fuming with perchloric acid destroys nitrate adequately and eliminates chloride if nitrate is added. Sulfate ion produces a small negative error (1 to 2%) when present up to 1N concentration. Elements that precipitate as salts
EXPERIMENTAL
Table 1. Effect of Perchloric and Hypophosphorous Acid Concentrations (106.0mg. of bismuth taken)
Variable factors considered were initial perchloric acid concentration, amount of hypophosphorous acid added, and concentration of bismuth. Over the range of 0.1 to 2.OM perchloric acid, results were satisfactory (Table I) ; 5 to 15 ml. of hypophosphorous per 100 ml. of sample solution is sufficient. Typical determinations of bismuth are tabulated in Table 11. Precipitations were made from IN perchloric acid. Heating the sample solution prior to addition of hypophosphorous acid offered no advantage. The samples that were not washed with alcohol and ether gave satisfactory results, but a longer drying time was required. Bismuth concentration of the order of 1 mg. per ml. was s a t i s factory and convenient. Immediate filtration of the hot precipitating solution was necessary. When the solution was allowed to cool overnight, up to 10% of the precipitate was lost. INTERFERENCE
As the presence of phosphate interferes through the formation of mixed precipitates, any substance that would oxidize hypophosphorous acid under
HClO4 Concn., N 0.1 0.5 1.0 2.0 1 .o
Table li.
H3P02, M1./100 M1. Soln. 5 5 5 5 2 5 10 15
Bi Found, Mg. 106.1,106.4 106.0.105.7 io6.5: i05.8 106.2,105.6 105.7,105.4 106.4,105.9 106.0. 106.2 106.2;100.4
Range of Bismuth Concentration
H3P0Z Bismuth, Mg. Added, M1. Taken Found 5 26.5 25.4, 26.0, 25.3 50 26.5 27.0, 26.1, 2.5 26.4 46.2 46.4, 46.2 5 100 106.0 106.1,106.2 159.0 158.9, 159.4 106.0 106.0, 105.5” 159.0 159.7, 160.1* a Ethyl alcohol and ethyl ether washes omitted. Sample solution heated to nearly boiling before adding HPPOt.
Vol., M1. 100
VOL. 30, NO. 8, AUGUST 1958
1321
of hypophosphorous acid under the described conditions are scandium(III), zirconium(IV), hafnium(IV), thorium(IV), and tantalum(V). Tin, silica, and germanium are not soluble in this medium. Copper, silver, gold, mercury, antimony, arsenic, selenium, tellurium, and palladium are reduced to an insoluble form, usually the element. In separate experiments, 100 mg. of bismuth was determined in the presence of equal amounts Of lithiuni(I), Sodium(I), potassium(I), magnesium(I1).
calcium(II), zinc(II), barium(II), aluminum(III), lead(II), N(NH+), chromium(III), manganese(II), iron(II), eobalt(II), and nickel(III), which did not interfere. The solutions containing iron, manganese, and chromium were treated with 5 ml. of 6% sulfurous acid before addition of hypophosphcr o w acid to remove higher oxidation states. Perchloric acid concentration of 0.1N was used when potassium was present, to prevent precipitation Of potassium perchlorate.
LITERATURE CITED
(1) Cousin, J., J . p h a n . chzm. 28, 179
w,,
(2) &lawrow, ( 1923). Muthman, F., z, anorg, Chem. 13, 209 (1897). '3) Silverman, I,., Shideler, M., ANAL. CHEW26, 911 (1954). (4) VaninopL., Truebert~F.l Ber. 31, 1303 (1898).
for
December
1'
1957.
Accepted March 24, 1958. Work performed under auspices of LT. S. -4tomic Energy Commission.
Detection of Phthalic Acid Isomers and Benzoic Acid in Alkyd Resins by Infrared Absorption Spectrometry M. 1. ADAMS and M. H. SWANN Coating and Chemical laboratory, Aberdeen Proving Ground, Md. The three isomeric phthalic acids and benzoic acid can usually be detected in alkyd resins from the infrared absorption spectra of dried films. Preliminary identification of one or more of these acids improves the speed and accuracy of subsequent quantitative analysis.
I
spectrometric analysis has been investigated for the detection of the three isomeric phthalic acids and benzoic acid in alkyd resins. Such information is particularly valuable for increasing both the speed and accuracy of subsequent quantitative analysis by existing methods. The quantitative method for determining the phthalic acid isomers involves separation from the oils and benzoic acid, if present, by saponification, followed by multiple-component ultraviolet absorption technique (3). If the absence of any of these acids could be established prior to the quantitative determination, the number of points at which ultraviolet absorbances are measured would be reduced. More important, the accuracy of the determination would be increased through the use of feRTer linear equations in the calculation of acid concentrations. The quantitative determination of benzoic acid in alkyd resins (4) involves separation of the acid from the oil acids by a special extraction technique followed by a one-component ultraviolet absorption procedure. If the absence of benzoic acid could be established in advance, much time would be saved by avoiding the quantitative determination entirely. As indicated by Shreve (I), the use NFRARED
1322
ANALYTICAL CHEMISTRY
of isophthalic or terephthalic acid in place of phthalic anhydride in alkyd resins produces specific changes in the infrared absorption spectra of the resins. The presence of benzoic acid, a monosubstituted benzene, gives characteristic absorption differing from that of the disubstituted acids. Absorption characteristics in the 11to 15-micron region by which each of the four acids may be identified in the presence of each or all of the other acids, are illustrated, tabulated, and discussed. PROCEDURE
A double-beam infrared spectrophotometer (Perkin-Elmer Model 21) with sodium chloride optics was used. A thin film of the resin solution is spread evenly on a polished rock salt plate and the solvent is removed by vacuum drying in an oven a t 60" C. for 1 hour. The spectrum from 11 to 1.5 microns is scanned using instrument settings designed to give ample resolution for qualitative analysis. The spectrum is then examined for characteristic points of absorption ns indicated in Table I. DISCUSSION
The points of specific absorption used to identify the isomeric phthalic acids and benzoic acid are illustrated in Figure 1 and tabulated in Table I. Figure 2 represents the absorption spectra in this same region of various alkyd resins. The compositions and concentrations of these resins and the interpretation of the absorption curves are given in Table I. The actual concentrations were determined by applying the ultraviolet quantitative techniques mentioned.
Spectra 1, 2, and 3 in Figure 1 are from dried films of alkyds containing phthalic anhydride, isophthalic acid, and terephthalic acid, respectively. The terephthalic acid alkyd was prepared in the laboratory especially for this purpose. Because a resin was not available in which benzoic acid was present without a phthalic acid isomer, the spectrum of ethyl benzoate is illustrated in spectrum 4 of Figure 1. Diethyl and dibutyl esters of phthalic anhydride produce spectra shoning the same points of absorption as an o-phthalic alkyd. Both ethyl benzoate and diethyl phthalate produce additional weak absorption bands from their ethyl group in the 11.4- to 11.5-micron region. Such absorption does not appear in a phthalic anhydride alkyd resin film and should not appear in an alkyd containing benzoic acid. The spectra of several commercially available isophthalic-benzoic acid alkyds were examined. In all cases, strong absorption a t 14.06 to 14.16 microns occurred because of the monosubstitution on the benzene ring. This corresponds to the absorption produced by ethyl benzoate. There mas no absorption from 11.4 to 11.5 microns. In alkyd resins containing combinations of the isomeric phthalic acids and/or benzoic acid, the points of specific absorption indicated in Table I and spectra 1 through 4 in Figure 1 remain well defined except for ophthalic acid. T h e n it is present with isophthalic acid (Figure 2, spectrum 6), the absorption a t 13.45 to 13.50 microns shows only as a shoulder on the isophthalic acid band. The 14.16 to 14.20 peak also will appear only as
