arc shown in Table 111. T h e averagv relative errors are 2.0 a n d 1.6% for niobium and tungsten, respectively. I n analyzing synthetic mixt’ures cont’aining niobium and tungsten together Iritli molybdenum, titanium, and tantalum, no interaction of the latt,er three with niobium or tungsten was observed. hIolybdenum appears to he reducwl t.0 the trivalent state in the procedure. and the molybdenum(II1). titanium. and tantalum do not affect t h r formation of the niobium- and tungstrn(V)-thiocyanate complexes. B>. contrast. a molybdenum-tungsten interaction was noted a t lower concentrations of the strannous chloride-hydrochloric acid reagent, the characteristic oranpc of tho niolybdenuni(V)-thiocyanate lwing obtained not with molybdenum alone. hut when tungsten was present with molybdenum : this is similar t,o the well known influence, of copper and iron on tlw formation of the molybdenuni(V)thiocaynnate complex ( 5 ) and to the act,ion of titanium and iron in proniotiiiy the formation of thiocyanate complexes of tunpstrn and vanadium ( 1 7 ) . The niobium and tungsten results for Sational Bureau of Standards (YES) saniples of stainless steel, cobaltbasc alloy. and soiii~composite Ptandartls a r c prescntect in Table IT‘. For nitrbium. over the range 0.30 to 3.15y0,and for tungst’en. over the range of 0.072 t ( J 4.50% the average relative errors arc’ 2.4 and XO%, respectivelj-. H o w i - e r . the S B $ valurs for samples 1233. 123b. 160a. 167. a n d 168 are only provisional. Furt1ic.r. thc methods used in oht’aining the SBS values are tediouh and tiine-c.onsuniing. and are accurate only when used 1)y an experienced analyst,
This method is fast enough to be useful in routine analyses, and is considerably more rapid than the tentative A S T l I hydroquinone method (2). Apparently a single hydrolytic precipitation gives sufficient separation of the mixed oxides from the large amounts of iron, chromium, nickel, and cobalt present in the various NBS samples analyzed. Although these samples contained up t o 4% molybdenum, 0.3% titanium, 1% tantalum, and varying amounts of other elements, no corrections for interfering elements were necessary. The absorptivities of tantalum. titanium, and molybdenum are 90 small that the amounts in the samples would not cause appreciable error. I n addition, not all the titanium and molybdenum would be collected in the niiyed-oxide precipitate, and most of the molybdenum so collected would be volatilized on ignition of the precipitate, especially if the ignition proceeds for a long period. Thus it is probable that the method could be applied to samples much higher in titanium and molybdenum without the necessity for any corrections. ACKNOWLEDGMENT
The assistance of Ernest G. Buyok and Howard S. Karp of the United States Steel Corp. Applied Research Laboratory in developing and testing the proposed method is gratefully acknowledged. LITERATURE CITED
(1) Alimarin, I. P., Podvalnaja, R. L.. Zhzrr. ilnal. K h i m 1, 30 (1946).
( 2 ) d m . Soc. T:sting
hhterials, Philadelphia, Pa., .A.S.T.?rl. Methods for Chemical Analysis of ?*Zetals,” pp.
150-7, 1956. (3) Bacon, A,, hIilner, G. W. C., Anal. Chim. Acta 15, 129-40 (1956). (4) Crouthamel, C. E., Hjelte, B. E., Johnson, C. E., A x . 4 ~CHEM. . 27, 507-13 (1955). ( 5 ) Crouthamel, C. E., Johnson, C. E., Zbid., 26, 1284-91 (1954). (6) Dinnin, J. I., Zbid., 25, 1803-7 (1953). 17) Freund, Harry, Levitt, A. E., Ibid., 23, 1813-16 (1951). (8) Freund, Harry, Wright, L. M., Brookshier, R. K., Zbzd., 23, 781-4 (1951).
W.F., Lundell, G. E. F., Bright, H. .4., Hoffman, J. I., “Applied Inorganic Analysis,” 2nd ed., pp. 60910 W’iley,New Pork, 1953.
(9) Hillebrand,
(10) Zbid., pp. 689-93. (11) Ikenberry, Luther, Martin, J. L., Boyer, R. J., ANAL.CHEX. 25, 1340-4 (1953). (12) Kanzelmeyer, J. H., Ryan, Jack, Freund, Harry, J . A m . Chem. SOC. 78, 3020-3 (1956). (13) Kassner, J. L., Garcia-Porrata, -4sdrubal, Grove, E. L., Axax,. CHEW27, 492-4 (1955). (14) Lauw-Zecha, A. B. H., Lord, S. S., Jr., Hume, D. N., Zbid., 24, 1169-73 (1952). (15) Marzys, -4. E. O., Analyst 79, 327-38 (1954). (16) Ibid.,80, 194-203 (1955). (17) Mundy, R. J., ANAL. CHEN. 27, 1408-12 (1955). (18). Palilla, F. C., Adler, Korman, Hiskey, C. F., Zbzd., 25, 926-31 (1953). (19) Pigott, E. C., “Ferrous Analysis,” PD. 315-16, Wiley, Sew York, 1953. (20i Ib?d., pp. 805-10. (21) Telep, George, Boltz, TI. F., ANAL. CHEK 24, 163-5 (1052).
RECEIVED for reviexy Sovember 4, 1958. Accepted February 4, 1959. Presented in part at Ninth Annual Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Alarch 1958.
Infrared Determination of Nitrocellulose in Mixtures of Cellulose Resins HELEN M. ROSENBERGER and CLARENCE J. SHOEMAKER Chemical Research a n d Engineering Department, A.
b Nitrocellulose can b e determined quantitatively in the presence of other cellulose resins b y utilizing the characteristic 1 1.92-micron absorption band. The method described is r a p i d a n d simple. The results obtained on synthetic mixtures of known composition indicate a maximum deviation of I t l % and a mean deviation of +0.4% as determined from four separate samplings of each mixture.
P
B. Dick Co., 5700 West
Touhy Ave., Chicago 48, 111,
plasticized solutions of nitrocellulose are widely used in protective and decorative coatings. In the graphic arts field they are the basis for lacquers and paper coatings. In these formulations the major resin component, nitrocellulose, is frequently used in conjunction with other compatible resins such as cellulose acetatc. cellulose acetate propionate, and cellulose acetate butyrate. Modified IG~IIESTLD,
maleic rosinq, ~~licnolformaldeliyde resins, and phthalic alkyd resins are also incorporated into such coatings. These coatings may also contain traces of aldehydes, alcohols, and plasticizers. The nitrocellulose employed in these mixtures is usually of the R S (estersoluble) type containing 12.0% nitrate nitrogen. Frequent analysis of such coating materials required a rapid method for VOL. 31, NO. 8, AUGUST 1959
1315
determining the percentage of nitrocellulose on a dry basis within h l % , The chemical methods for determining nitrocellulose in lacquers and similar materials, although accurate, had many drawbacks. Nitrocellulose has been determined from the nitrogen content, as measured by the evolution of nitric oxide, using the nitrometer method (1-3, 5 ) and volumetrically ( 6 ) by
Table I.
dissolving the sample in hot acetic acid, boiling with a ferrous salt reagent, and titrating the resulting ferric ion with a standard titanous chloride solution. 4 gravimetric method (8) involving the isolation of nitrocellulose by solvent precipitation and a colorimetric method (7') have been described. The nitrometer method requires a considerable amount of mercury and a n
Analysis of Nitrocellulose Mixtures
Other Component Cellulose acetate propionate
Xitrocellulose, % Mean X s Found 70.6 70 3 70.0 70.6 69.8 51 0 51.9 51 7 51.7 51.3 51.9 33 0 33.6 33 4 32.8 33.6 33.5 11.9 11.0 11 3 11.2
Present 70 0
Est. Std. D ~ v . ~ 0.415
0.283
0,288
0.436
11.1
Cellulose acetate
80.0
60 5
Cellulose acetate
42 3
23 0
Cellulose acetate butyrate
5 0
1. 0
11.1 79.1 79.5 79.1 80.4 61.3 61.0 61.2 60.8 41.5 41.6 41.9 41.9 22.5 23.2 22.9 22.6 5.4 .5 . 2 5.1 5.1 1.6 1.2
79 5
0 . 613
61 1
0,427
41 7
0.208
Cellulose acetate Celluloee acetate propionate Celluloee acetate butyrate
25.0
E thylcellulbse
33.5
Modified maleic rosinb
52.0
Phthalic alkyd resinc
80.0
* 8 = d Z ( X - F)'/(n - 1). * Amberlac D-96. Duraplex A-27.
e
1 3 16
ANALYTICAL CHEMISTRY
PROCEDURE
-4sample of the lacquer or a solution 22 8
0 316
5 2
0 141
1 3
0.224
24 9
0.382
34 0
0.173
51 5
0.265
80.6
0.173
1.1
1.4 24.4 25.2 24.8 25.2 34.2 33.9 33 8 34.0 51.3 51.7 51.7 51.2 80.8 80.4 80.6 80.5
experienced analyst, and is time-colisuming. The volumetric determination, although rapid in application, necessitates the digestion of the sample, lengthy preparation of the reagents, and frequent standardization. Solvent precipitation with subsequent gravimet'ric analysis is not applicable in the presence of the other resins listed, because most' of the resins show similar compat'ibility and solubility characteristics. The colorimetric method entails less effort and affords excellent results in most cases; however, it requires saponification of the resin and is subject to significant interference from rosin-type resins and free aldehydes. The infrared absorption spectruin of nitrocellulose exhibits strong bands a t 6.05 and 7.82 microns, characteristic of covalent nitrate groups, and a strong absorption band a t 11.92 microns rclated to the nitrate group. Because the 11.92-micron band does not appear in any of the other cellulosics or in any of the resins generally used in combination with nitrocellulose, this band xas investigated in the quantitative determination of nitrocellulose. The 6.05- and 7.82-micron b.nn d s are less desirable for quantitative determinations, because most resins and plastics (9) sho\y strong absorption bands in the 6- to 8-micron region. Furthermore, in the use of a single-beam spectrophotometer, the absorption bands of atmospheric water vapor are superimposed upon tlic sample over this portion of the spectrum.
of the extracted coating material was poured slowly, with st'irring, into warm water and the resulting precipitate n-as collected by filtration or decantation. The precipitate was dried by pressing it between folds of hardened filter paper. The pigmented resinous material was dissolved in a suitable solvent (acetonr, methyl ethyl ketone, etc.) and the pigment x i s separated b y high-speed centrifugation. I n the few cases n-hwe a colorless solution was not obtained, the method of Newburger (4) was used and the solvent was finally evaporated to leave the colorless resin. A sample of the dried film, sufficient' to give a 1 to 2% solution, was weighed into a volumetric flask or cylinder, dissolved in acetone (ACS reagent grade), and diluted to volume. A portion of the solution was placed in a suitable liquid cell and the absorbance w:is measured a t 11.92 microns. using the base-line technique with acetone as a blank. The nitrocellulose content v a s then determined from a calihration curve prepared from pure nitrocellulose. -4 straight-line calibration curve was obtained by plotting the absorbance readings against the nitrocellulose content of standards prepared from RS nitrocellulose (12.0% nitrate nitrogen) over a range of 0 to 5% on a dry weight basis.
XI1 measurements were made on a Perkin-Elmer single-beam, recording s p e c t r o p h o t o n i e t e r , Model 12B, equipped with a sodium chloride prism and 0.05-mm. sodium chloride cells. DISCUSSION
The determination of nitrocellulose in mixtures of other resins is difficult and time-consuming. Some methods are also hazardous. The infrared procedure represents a rapid, convenient method, sufficiently accurate for many practical applications. The method is not subject to interferences from any other resins normally compounded with nitrocellulose. This includes any resin which can be precipitated from the solvent solution with 17-ater. Traces of aldehydes which may be occluded in the film do not interfere. The method n-as
evaluated by measuring the nitrocellulose content of carefully prepared synthetic mixtures. Four separate determinations were made on each mixture (Table I). For rapid control work a single determination may be expected to show a maximum deviation of = k l % nitrocellulose. The over-all accuracy of the method is reflected in the averaged, estimated standard deviations of 0.31001, over a range of samples having a nitrocellulose content from 1 to 80%. ACKNOWLEDGMENT
The authors are grateful to the A. B. Dick Co. for permission to publish this work. LITERATURE CITED
(1) Am, Soc. Testing lfaterialq, .ISTlI
Standards, Part 4, “Standard Specifications and Tests for Soluble Xitrocellulose,” pp. 361-9, D 301-50, 1952. (2) Furman, N. H., ed., “Scott’s Standard Methods of Chemical Analysis,” 5th ed., Vol. I, pp. 650-2, Van Nostrand, Ken- York, 1939. (3) Genung, L. B., ANAL.CHEXI. 22, 401 (1950). (4) Newburger, S. H., J . ilssoc. Om. Aqr. Chemists 39, 259-60 (1956). (5) Pitman, J. R., J . Soc. Chem. Znd. (London) 19, 983 (1900). (6) Shacfer, W. E., Becker, IT. K., ANIL. CHEM2 5 , 1226 (1953). ( 7 ) Swann, M. H., Zbid., 29, 1504 (1957). (8) Swann, AI. H., -4dams, RI. L , Esposito G. G., Zbid., 27, 1426 (1955). (9) U. S. Dept. Commerce, “Infrared Spectra of Plastics and Resins,” PB 111338 (1964).
RECEIVED for review Xovember 13, 1058. ilccepted March 23, 1959.
Quantitative Determination of Platinum in Alumina Base Reforming Catalyst by X-Ray Spectroscopy ARNOLD J. LINCOLN Research and Development Division, Engelhard Industries, Inc., Newark, N. I .
ELWIN N. DAVIS Sinclair Research laborafories, Inc., Harvey,
111.
,X-ray spectrophotographic techniques are sufficiently fast and accurate for platinum assay in new refining techniques requiring a catalyst containing platinum metal. Sample preparation is relatively simple, requiring only grinding and calcining to reduce all samples to a uniform condition. Two methods of calibration are proposed depending upon the x-ray tube supplying the exciting radiation. The standard deviation of the method is about 0.0025% a t the 0.6% platinum level. The elapsed time between receipt of a sample and the result is about 3 hours, about 30 minutes of which requires the operator’s attention.
ing catalyst utilizing a fluorescent x-ray spectrograph. With minor modifications, they should be adaptable to the determination of most of the impurities of interest found in this type of catalyst. The catalyst described is usually manufactured in extruded form which can be reduced to a fine powder by grinding. This is desirable for x-ray spectrographic work to give a reproducible sample radiating surface. Excellent studies using x-ray spectrographic techniques in the analysis of powders have been reported. Equipment. This work was conducted in two laboratories. Identical equipment was used, except for t h e x-ray tubes supplying t h e exciting radiation. I n one laboratory a molybdenum target tube was used; in t h e other, a tungsten target. Although both tubes were satisfactory, a n alternative procedure was necessary with the tungsten tube.
I
N BUSINESS transactions involving the
use of platinum or the platinum group metals, the accurate determination of platinum content is important. A relatively small error in an assay can result in a large monetary gain or loss. The x-ray spectrograph suggested a convenient, reliable, and accurate procedure for the quantitative determination of platinum on alumina catalyst. The methods described were designed for a platinum-on-alumina base reform-
North American Philips Co., Inc., x-ray spectrographs Lvere used. Machlett OEG 50 tungsten and molybdenum target tubes n-ere operated a t 60 kv. and 50 ma. Jlilliampere stabilizers maintained the current through the x-ray tube constant to within 0.1%. Lithium fluoride crystals \\-ere used as
the dispersing elements. The collimating system employed open tube primary and parallel plate secondary collimators. A Geiger counter n-as used as the detector. For ease and accuracy in time measurements, automatic electric stop clocks, reliable to 0.1 second, were substituted for the standard timer. The sample holder, specifically designed to fit the standard specimen tray, permitted a backloaded specimen with a smooth flat surface with an area of 1.19 square inches and containing approsimately 4.5 grams of catalyst. Platinum Analytical Line. The platinum spectrum of a typical platinum-on-alumina reforming catalyst in Figure 1 s h o n s t h a t the L , and Lo lines possess intensities well above background and of a suitable magnitude for comparative measurements. With t h e molybdenum tube t h e background region in t h e vicinity of the Lp line is smooth and nearly horizontal, while the L , region is irregular because of the molybdenum lines of the tube and some tungsten contaminant lines. Therefore, the Lo1 line at 32.29’ 29 was chosen as the analytical line with the molybdenum tube. Figure 2 shows a manual count over the Lpl line and the accompanying VOL 31, NO. 8, AUGUST 1959
1317
