V O L U M E 23, NO. 3, M A R C H 1 9 5 1 Pipets adjusted with water have to be adjusted to the actual delivery of 25 and 5 ml. of carbon tetrachloride. DISCUSSION
This procedure is applicable to gasolines (mixtures of paraffins and naphthenes) from about six carbon atoms in the molecule, to oils and paraffin waxes if they are soluble in carbon tetrachloride a t 20" C. The folloiving hydrocarbons are stable against antimony pentachloride: all saturated hydrocarbons containing only
C CHB--, -CH2-,
I
and C-7-C
c groups, such as n-paraffins, cyclohexane, and compounds with quaternary carbon atoms such as 2,2-dimethylbutane. Thus, the true n-paraffi content of a hydrocarbon mixture is found by this method only if the other hydrocarbons listed in this group are absent; otherwise, their percentage is included in the n-paraffin content. The following hydrocarbons react with antimony pentachloride t o form products which are insoluble in carbon tetrachloride: compounds with a tertiary carbon atom such as isoparafhs, substituted cycloparaffins (naphthenes), and olefins. Aromatic compounds and oxygenated compounds react with antimony pentachloride to form products which are partially eolublc in carbon tetrachloride; thus they interfere with this
495 method if present in considerable amounts, and must be removed before antimony pentachloride is applied, by treatment with sulfuric acid according to well-known procedures. This method is not restricted to mixtures of paraffins and naphthenes, but applies also to olefins, alcohols, ketones, aldehydes, fatty acids, etc., after these compounds have been transformed into paraffins by adequate hydrogenation. The accuracy of this method varies with the molecular weight of the sample; in oils and paraffin waxes the average absolute error is about 2 to 4% of the total sample and in gasolines the error is sometimes greater (3 to 6%), as may be learned from the data in Table 11. I t is probable that by a further study of the individual reaction rates of hydrocarbons R ith antimony pentachloride and by slight modifications of the procedure this range of errors may be narrowed. ACKNOWLEDGMENT
The experiments described in this paper were carried out by the author in 1940 a t the Ammoniaklaboratorium Oppau of the former I. G. Farbenindustrie Aktiengesellschaft, Ludwigshafen/ Rhein, Germany. Appreciation is expressed to the Badische Anilin- und Sodafabrik, Ludnigshafen /Rhein, for permission to publish this work. LITERATURE CITED
(1) Hibbard and Cleaves, A N ~ LCHEM.. . 21,486 (1949). (2) Leithe, W., 2.Unlersuch. Lebensm., 67,441(1934). (3) Schaarsohmidt and Marder, Z . angew. Chem., 1933, 151. RECEIYED April IO, 1950.
Infrared Analysis of Five C,, Aromatics JOHN A. PERRY' Monsanto Chemical Co., Texas C i t y , Tex.
The need for a means of analvzing mixtures of five Clo aromatics led to the method presented, which was designed to be rapid and accurate, and to have maximum simplicitj of execution. No dilution of standards or of samples was required in either calibration or analysis. Measurements of cell length and absorbancy were eliminated by the condition of normalization and the use of reference wave lengths, respectively. The acciiracy is show-n
I
S T E R E S T in the composition of isomeric butyl and diethylbenzene mixtures boiling between 16.5' and 190" C. led to the development of a method for determining the composition of such mixtures. The analysis was set up using the ult'raviolet region, but was found inadequate for complete determination of the individual isomers (?). A mass spectrometric determination ( 5 ) of traces of the Ci0 isomers in ethylbenzene has been reported, but determination of concentrations of the individual isomers was not indicated. S o analysis of these mixtures by Raman spectrometry has been reported, although it has been indicated as a possible approach ( 4 ) . Fractionation is not a sufficiently powerful tool to permit easy separation of the isomers, and no rapid and accurate chemical methods have been found in the literature. Resort was therefore made to infrared spectrophotometry: about 45 minutes are required to obtain results having an average absolute error of 0.5%. 1 Present address, College of Chemistry a n d Physics, Louisiana State University, Baton Rouge, La.
to compare favorably with similar reported work, the error being 0.570 absolute over the whole percentage range. An infrared normalized multicomponent analysis of hydrocarbon liquids can be set up under the following restrictions, each of which materially simplifies performance of the analysis: assumption of validity of Beer's law, no dilution of standards or samples, and no knowledge of the length or absorbancy of the rock salt cell.
APPARATUS
A Perkin-Elmer Model 12C spectrometer equipped with a Model 51 breaker-amplifier and Brown recorder was used. HYDROCARBONS
Sources and given purities of the hydrocarbons used were an follows: Compound
Purity, Mole 7c
o-Diethylbenzene m-Diethylbenzene p-Diethylbenzene Isobutylbenzene sec-Butylbenzene
99.95 0.03 99.93 f 0.04 99.93 * 0 . 0 2 99.87 * 0 . 0 9 99 minimum f
Source Sational Bureau of Standards National Bureau of Standards National Bureau of Standards National Bureau of Standard8 Phillips Petroleum Co.
DEFINITIONS
The following terms and meanings are used in this paper:
A = l o g 3 = Kcd I
496
ANALYTICAL CHEMISTRY
Table I.
Wave Lengths, Slit Widths, and Shutters Used
Substance o-Diniethylbenzene m-Diethylbenzene p-Diethylbenzene dec-Butylbenzene Isobutvlbenzene sec-Buiylbenzene (to track monochromator)
Analytical Slit width, A, P mm. Shutter 10.65 0.375 L i F 11.54 0,450 L i F 8.92 0,262 Glass 10.00 0.330 L i F 8.56 0.255 Glass
Reference Slit width, A, ~r mm. Shutter 10.53 0.368 L i F 11.40 0.440 L i F 8.79 0.255 Glasa 10.53 0.368 L i F 8.79 0.255 Glasa
9.78 0.130
lation of the interacting gain and balance controls. However, this identity is not necessary; it is only necessary that the pen fall accurately on infinity (log l/zero), and this can be achieved with only a rather coarse adjustment of the balance control. With the shutter in the beam, and after deflection of the pen by the test signal as has been indicated, the ruling for infinite absorbancy is placed directly under the pen by a manual lateral shifting of the metal scale. Placement of the pen within the 0.125-inch (0.6-cm.) lateral range available to the metal scale can be easily accomplished. The deflection for lo was made to fall somewhat short of full scale, and the reading from the log 1/N scale was subtracted from the corresponding reading for I ; log 1/z - log l / Z 0
where
.4 = absorbancy (analytical absorbancy indicates an absorb-
K
=
c = d = Zo =
Z
=
ancy a t an analytical wave length; reference absorbancy, an absorbancy a t a reference wave length) (8, 10) absorbancy coefficient concentration cell length intensity of incident radiation intensity of transmitted radiation Absolute error = ( % known) - (% found) ( % known) - (70found) Relative error = ( % known) PROCEDURE
=
log I o / l
131 iiie:tn., of these techniquea, the eight absorbancies used in this analysis could be accurately obtained in about 20 minutes Absorbancy Coefficients. Absorbancy coefficients of the diethylbenzene isomers, sec-butylbenzene, and isobutylbenzene were obtained by measuring absorbancies of these compounds without dilution by solvents. Wave-length settings were always approached from shorter wave lengths, and slit widths approached from smaller slit widths. Occasional negative figures werr produced in the subtraction of the reference absorbancies, and these were handled identically in the calculations, with preservation of sign. The relative values of the coefficients are given in Table 11.
Selection of Absorbance Bands, Slit Widths, and Shutters. ANALYSIS To secure good intercomparison of spectral position and band Saniples were also measured without dilution, by the sitiiie absorbancy, spectra of all hydrocarbons to be included in the procedure in which the absorbancy coefficients were obtained. analysis were superimposed on the same chart. Because the The method of Crout (%) was used in calculations. Results analysis wm intended t o apply equally well to all percentage for one sample could be calculated in 10 to 15 minutes. ranges, absorbance bands were selected which have about equal All results were normalized; this not only canceled out changes absorbancy. Of secondary importance was the fact' that the in cell lengt,h but allowed cells of any length to be used so long bands show only slight mutual interference, although this is as prohibitively high (roughly, over 1.1) absorbancies did not desirable. occur. Analysis of synthetics and independence of results from Careful scanning of the pure hydrocarbons establjshed the cell length are shown in Table 111. Because the cell length need wave lengths of the selected analytical bands to better than 0.004 not be known during calibration or analysis, it should be chosen micron. The 9.78-micron band of sec-butylbcnzene was used as a to have the maximum permissible length, so as to improve det,ermeans of subsequently tracking the n-ave-length shift of the monomination of the smaller coefficients and absorbancies. The cell chromator with temperature. Three wave lengths, characterized length should not change q-hile absorbancy coefficients are being by low absorbancy for all coniponcnts and by relative nearnew obtained. Although this constancy was not checked by actual to the analytical wave lengths, were also selected to furniyh measurement, it is strongly implied by the analytical results in reference absorbancies to be subtracted from relevant ne:trt)y Table 111. Precision and accuracy of the method are shown in analytical absorbancies, thereby accurately canceling out the T:il)le IT'. absorbance of the cell. Nit widths were used which would furnish at the selected wave lengths thermocouple signals of approximately 3 microvolts, which were sufficient to eliminate error from noise with the inxtruTable 11. Relative Yalues of Absorbancy Coefficients ment a t hand. This was considered preferable t o retention of Wavesmaller slit widths. Length To attempt to reduce errors from stray light, a glass shutter was -&onri:$;: AbsorbIsoBCC0mPused for all wave lengths longer than 6.2 microns, and a lithium ancy butylButylDiethyl- DiethylDiethylfluoride shutter a t positions beyond 9.2 microns. Figures, P benzene benzene benzene benzene benzene 0.031 0.002 0.215 -0.063 The combinations of analytical and reference lvave lengths, 8.56-8,79 0.870 0.529 -0.083 0.053 0.003 10.00-10.53 -0.068 slit widths, and shutters used are shown in Tahle I. 10.65-10.53 -0.074 -0,142 0.395 -0,021 -0,013 -0.079 0.004 0.056 0.591 0,064 Method of Obtaining Absorbancy. The following method 1;: ~ ; ; ~ ~ , ~ O 0.244 0.023 0.071 0.020 0,760 was devised for the Perkin-Elmer system which utilizes a chart ruled for log 1 / N , incorporates means for putting test signals into the amplifier, and uses the Brown Table 111. Analyses of Synthetics, Weight Per Cent recorder. The method must be altered if necessary K Fa Fb K Fa K F" K Fa K Fb for use on systems having different characteristics. ~
€0
-4test signal of 0.1 microvolt was used in conjunction with all readings for absorbancy. Introduction and subsequent removal of the signal immediately before each reading tended to ensure that all readings (or settings of the pen) were taken on the same side of true balance, so that errors from recorder dead space were minimized. The ruling of the scale used-log l/N-implies that the full-scale signal should be identically that of Io, the incident radiation. Achieving this identity ordinarily requires time-consuming manipu-
Iaobutylbenaene 22.2 22.1 21.8 47.0 46.1 0.0 0 0 21.5 21.2 13.5 14.2 13.7 rec-Butylben23.6 23.3 23.5 31.8 31.4 33.8 33.9 15.5 16.0 17.6 17.7 18.0 sene zene m-Diethylbenaene pDiethy'benzene
22.4 22.8 22.8
0.0 0.9 36.6 36.2
7.5 8.1
9.1 9.9 9.8
11.2 11.4 11.6
0.0 1.0 11.3 11.2 16.6 16.2
18.3 17.5 18.7
20.5 1 9 . 8 20.2 21.2 20.0 18.3 19.3 38.9 38.5 41.4 40.7 40.0 K . Known. F. Found. 0 0.100-mm. cell used. b 0.203-mm. cell used. ~~
V O L U M E 23, NO. 3, M A R C H 1 9 5 1 Table I\’. Reference Present method (0)
(3) (1).
(6)
497
Survey of Comparable Analyses
Average No. Components 5
2.6
Average Absolute Error
0.5 0.5
4
0.9 0.4
4
1.0
3.6
Average Relative Error 2.i 1.8 4.3 1.5 4.2
5 Ten-component analysis not included (average absolute error, 0.7% : average relative error, 16.9%).
component analysis of liquids where all components sought total 100% and are generally present in concentrations greater than 3 to 5%, and in which high-absorbancy techniques are not used. Results are shown in Table IV. LITERATURE CITED
Coggeshall, K. D., ANAL.CHEM.,22, 381 (1950). Crout, P. D., Trans. Am. Inst. Elec. Engrs., 60, 1235 (1941). Friedel, R. A , , Pierce, L., and McGovern, J. J., ANAL.CHEM., 22, 418 (1950). Fromherz, H., Buren, H.. and Thaler, L., Angew. Chem., A59, 142 (1947).
COMPARISON OF RESULTS
The recent literature was consulted for analyses of liquid multioomponent solutions, in order to obtain a means of judging the precision and accuracy of the present analysis. The survey is not claimed to be complete, but the results are probably representative a t this time of this type of work-namely, infrared multi-
Johnson, S. E. J., ANAL.CHEM.,19,305 (1947). Kaye, W. I., and Otis, M. V., Ibid., 20, 1006 (1948). Perry, J. A . , Sutherland, R. G . , and Hadden, N., Ibid., 22, 1122 (1950).
Pirlot, Bull. aoc. chim. Belges, 58, 28 (1949). Saier, E . L., and Coggeshall, N. D., ANAL.CHEM.,20, 812 (1918). Wright, N., IND. ENG.CHEM.,ANAL.E D . , 13, 1 (1941). RECEIVED July 13, 1950.
Colorimetric Determination of Rhenium EMIL E. MALOUF AND MERWIN G. WHITE Kennecott Copper Corp., Utah Copper Division, Garfield, Utah A method is described for the quantitative colorimetric determination of rhenium in samples containing as little as 0.1 microgram to 2.5 mg. of rhenium per gram of sample. Determinations of rhenium have been made in the presence of 125 mg. of molybdenum in a volume of 25 ml. The molybdenum is separated from the rhenium as a metalorganic compound, formed with ethyl xanthate, and extracted from a dilute acid solution with an organic
I
T BECAME desirable to vrork out a method for the quantita-
tive determination of small amounts of rhenium in the presence of large amounts of molybdenum. A method that would be faster, and if possible more accurate than existing methods, was sought. -4 procedure has been developed which not only permits a quantitative rhenium determination to be made much more rapidly, but also lends itself to a mass analysis technique. The new method differs from the older distillation techniques in that the distillation of rhenium from an acid solution with its attendant difficulties is eliminated. The molybdenum, a common interferring ion in ores and solutions containing rhenium, is separated from the rhenium as a metalorganic compound, formed with ethyl xanthate, and extracted from a dilute acid solution with an organic solvent mixture. Two other methods of rhenium analysis were previously used. The method of Hiskey and Meloche ( 9 ) was modified by making a n ether extraction to concentrate the rhenium color for easier color comparisons. A modified Hoffman and Lundell(4) method was developed a t the Chase Brass Laboratory (7). A colorimetric method for determining rhenium, limited to samples containing no more than 1 mg. of molybdenum, which was precipitated with a-benzoinoxime, was developed by Melaven and Whetsel (6). Geilmann and Bode ( 1 ) did considerable work on the colorimetric method for the determination of rhenium by forming the rhenium thiocyanate color complex. As various metallic salts precipitate molybdate ions and not perrhenate ions, separations of molybdenum and rhenium based on the insolubility of calcium molybdate, barium molybdate, and lead molybdate were tried, but later abandoned in favor of the
solvent mixture. The rhenium is determined by forming the rhenium thiocyanate color complex and measuring the transmittance of the solution with an electrophotometer. A precision of *270 has been obtained over the specified concentration ranges. The method is readily applicable to the mass analysis techniques of routine analytical laboratories, and permits a rapid and accurate search for rhenium in minerals.
xanthate method because of its greater efficiency. Tlie use of xanthate for the srparation of molybdenum had been worked out previously in this laboratory in some detail by Hansen (2) and Hurd ( 5 ) . REA GENTS REQUIRED
Sodium Ethyl Xanthate Solution. Dissolve 40 grams of xanthate in 60 ml. of distilled water, filter, and dilute the filtrate to 100 ml. The water solution of xanthate should be prepared fresh daily. Sodium Thiocyanate Solution. Dissolve 200 grams of C.P. sodium thiocyanate in distilled water and dilute to 1 liter with distilled water. Stannous Chloride Solution. Dissolve 350 grams of C.P. stannous chloride in 250 ml. of concentrated hydrochloric acid a t room temperature with occasional stirring. Add 250 ml. of distilled water and dilute to 1 liter with 1 to 1 hydrochloric acid. Add a few pieces of tin to keep the solution reduced. Ether for Dilution. Place 25 ml. of 1 to 2 hydrochloric acid, 2 ml. of the sodium thiocyanate solution, and 2 ml. of the stannous chloride solution in a 125-ml. glass-stoppered separatory funnel, and add 30 ml. of purified ethyl ether. Shake for 30 seconds and allow the two resulting layers to separate. Drain off the acid layer and reserve the ether layer. Standard Rhenium Solution. Dissolve 0.0775 gram of pure potassium perrhenate in distilled water, add 25 ml. of 6 iV sulfuric acid, and dilute to 500 ml. with distilled water. This gives a solution containing 0.10 mg. of rhenium per ml. An 0.01-mg. rhenium solution may be prepared by a tenfold dilution with 0.3 N sulfuric acid. PROCEDURE
Reparation of Standard Curve. Use a solution containing 0.01 mg. of rhenium per ml. Pipet into 250-ml. beakers 1-, 2-, 5-, and
