Table 1. Determination of Carbon Monoxide in Synthetic Gas Mixtures Dev. from Carbon Monoxide, % Av. Present Found Recovery Recovery 1.512 1.531 1.210 1.221 1.045 1.051 0.742 0.754 0.540 0.554 0.330 0.320
1.508 99.74 0.16 1.540 100.73 0.83 1.208 99.83 0.07 1.230 100.73 0.83 1.042 99.71 0.19 1.045 99.43 0.47 0.742 100 00 0.10 0.772 102.40 2.50 0.536 99.25 0.65 0.563 100.73 0.83 0.324 98.18 1.72 0.314 98.12 1.78 Av. and std. dev. 99.90 i 0.85%. Sample size used, 500 ml.
Table II. Determination of Carbon Monoxide in Synthetic Gas Mixtures (Higher and loKer concentration ranges) Sample Carbon Monoxide, % Size, M1. Present Found Recovery 100 2000 a
5.000 5.026a 100.52 0.050 0.058. 116.00 Each figure is average of three deter-
and it is connected to the Anhydrone and guard tube. The flow of oxygen is stopped and the stopcock of the sample bottle adjoining the combustion train opened. The stopcock which connected the sample bottle to the separatory funnel is then opened and adjusted to permit liquid displacement of the gas a t a rate of 20 to 30 ml. per minute, The solution of sodium chloride displaces the gas in the sample bottle by gravity, forcing the gas mixture through the combustion train. When the sample has been completely displaced, the stopcocks are closed. The system is then purged with oxygen for 15 minutes. After this time the flow of oxygen is stopped and the Ascarite tube disconnected from the assembly, n-iped with the chamois, and weighed. The increase in weight of the Ascarite tube is proportional to the carbon monoxide in the sample. An increase in weight of 1 mg. is equal to 0.501 ml. of carbon monoxide. Calculation. 0.501 X 100 yo co = A X V (ml.)
The results are presented in Table I. Periodical analyses of the same gas mixtures except for carbon monoxide indicated no blank value. Because this method is based on a gravimetric principle, the analysis of gas mixtures containing higher than l.5yGconcentrations of carbon monoxide would give better accuracy and precision than the analysis of mixtures with lower concentrations. Smaller sample sizes are indicated in such cases. When carbon monoxide is present in less than 0.1% concentrations, proportionally larger samples should be used to obtain satisfactory accuracy and precision. The results of triplicate analyses of gas mixtures are presented in Table 11. A liquid nitrogen trap can be incorporated in the assembly. This will freeze out saturated hydrocarbon varieties. A number of purifying and drying trains for specific gas mixtures as described by Adams and Simmons ( 1 ) may be used with this method.
n-liere
A
LITERATURE CITED
increase in weight of Ascarite tube, milligrams V = volume of gas sample, milliliters, a t standard pressure and temperature
minations.
=
PROCEDURE
RESULTS AND DISCUSSION
The microheater is turned on and allowed to reach operating temperature, 450" to 500' C. The apparatus is purged with oxygen (20 to 40 ml. per minute) for 10 to 15 minutes. Meanwhile the Ascarite absorption tube is wiped with a chamois cloth and weighed on a semimicro or microanalytical balance. A trace of glycerol is added to t.he tips of the Ascarite absorption tube,
A series of synthetic gas mixtures containing nitrogen (75 to 78%), oxygen (18 to 21%), carbon dioxide (0.03 to l.O%), unsaturated hydrocarbons (1.0 to 5.0%), and carbon monoxide (0.3 to 1.5%) was prepared and analyzed for carbon monoxide content. The accuracy of the analysis in the indicated range is to &0.85%.
(1) Adams, E. G., Simmons, N. T., J . Appl. Chem. (London) 1, Suppl. 1, 5-20 (1951). (2) Grant, G. A., Katz, Morris, Haines, R. L., Can. J . Technol. 29, 43 (1951). (3) Katz, Morris, Katzman, John, Can. J. Research 26F, 318 (1948). (4) Korbl, Jifi, Chem. listy 49, 858 (1955). (5) Korbl. Jiff. Mikrochim. Acta 1956, 1705. (6) Lysyj, Ihor, Zarembo, J. E., Microchem. J . 2,245 (1958). (7) Scott, .W. W., ' f S F d a r d Methods of Chemical Analysis, 5th ed., Vol. 11, p. 2350, Van Nostrand, New York, 1939.
.,
,
I
RECEIVED for review February 14, 1958. Accepted December 16, 1958.
Photometric Determination of Tantalum with Phenylfluorone C. L. LUKE Bell Telephone laboratories, Inc., Murray Hill, ,A photometric phenylfluorone method for the determination of traces of tanThe talum has been developed. interference of other metals is eliminated by virtually isolating the tantalum by solvent extraction from hydrofluoric-hydrochloric acid solution with methyl isobutyl ketone and by masking with (ethy1enedinitrilo)tetraacetic acid during the subsequent color development.
904
e
ANALYTICAL CHEMISTRY
N.J.
D
development of a photometric method for germanium it was found that tantalum and several other metals form red compounds of various intensities and hues with phenylfluorone (1). It seemed worthwhile to determine whether the color reaction could be made the basis of a practical method for the photometric determination of tantalum. It appeared probable that, by virtually isolating the URING
tantalum by extraction with methyl isobutyl ketone (2) and by masking any remaining interference with (ethylenedinitri1o)tetraacetic acid (EDTA), B satisfactory determination of tantalum could be made. This has proved to be true. REAGENTS
Standard Tantalum Solution (100 tantalum per ml.). Transfer
7 of
0.0500 gram of pure tantalum metal plus 2 ml. of hydrofluoric acid t o a covered platinum crucible. Add nitric acid dropwise with gentle heating until dissolution of the metal is complete and b r o m fumes have bern expelled. Cool, dilute t o 500.0 I d . ) and store in a polyethylene bottle. Buffer Solution (pH 4.5). Dissolve 500 grams of ammonium acetate in 500 ml. of water. Add 700 ml. of acetic acid followed by 2 grams of benzoic acid (as preservative) dissolved in 20 ml. of methanol. Dilute to 2 liters. Transfer 10 grams of &ox powdered gelatin to 1 liter of water in a beaker and heat in an 80" to 90" C. hot water bath, with occasional stirring, until the gelatin has dissolved. Cool. Mix the buffer and gelatin solutions and adjust the p H of the mixed solution with the aid of a p H meter to 4.5 by the addition of acetic acid or ammonium hydroxide. Phenylfluorone Solution. Transfer 0.0500 gram of phenylfluorone (2,3,7trihydroxy-9-phenyl-6-fluorone) to a 100-ml. beaker. Add 50 ml. of methanol followed by 1 ml. of hydrochloric acid and then stir until disgolved. Transfer to a 500-ml. volumetric flask and dilute to the mark with methanol. PREPARATION OF CALIBRATION CURVE
Working individually, transfer 0, 0.40, 0.80, and 1.20 ml. of standard tantalum solution (100 y of tantalum per ml.) to a 100-ml. platinum dish. Float the dish in an 80" t o 90" C. water bath and allow the tantalum solution to evaporate just to dryness with the aid of a gentle jet of air. Pipet 1 ml. 99) from a of hydrofluoric acid (1 polyethylene bottle to the dish and heat and swirl on a low temperature hot plate until the tantalum compound dissolves. Cool, add 5 ml. of 10% w./v. aqueous solution of the disodium salt of EDTA, swirl, and pour into a 50-nil. volumetric flask. Add 10 ml. of p H 4.5 buffer solution to the dish, swirl, and pour to the flask. Pipet 10.0 ml. of phenylfluorone solution to the flask, swirl to mix, and then allow to stand 30 minutes. Add 5 ml. of a saturated aqueous solution of boric acid to minimize the corrosive action of the hydrofluoric acid on the absorption cell, dilute to the mark with acetic 9), and mix. Immediately acid (1 measure photometrically at 530 mp in a 1-em. absorption cell using mater as the reference solution. Without delay rinse out the absorption cell containing the sample.
+
+
ANALYSIS OF SAMPLE
If the sample solution to be analyzed is acid, evaporate to dryness in a 100ml. platinum dish. If sulfuric or perchloric acids are present, continue the evaporation on a low flame until evolution of acid fumes just ceases. If the sample solution to be analyzed is alkaline, acidify it with hydrofluoric acid in a platinum dish and then evaporate to dryness. If sexivalent chromium is present, in either instance add 30% h y drogen peroxide dropwise to the acid
solution until the yellow color of the chromate disappears, before evaporating the solution to dryness. Cool, add 5 ml. of hydrofluorichydrochloric acid solution (20 ml. of hydrofluoric acid plus 20 ml. of hydrochloric acid plus 360 ml. of water in a polyethylene bottle), Heat while swirling on a low temperature hot plate until the residue has dissolved. Cool, pour into a 60-ml. separatory funnel, and wash-transfer with an additional 5-ml. portion of the mixed acids. Add 5 ml. of methyl isobutyl ketone, stopper, shake vigorously for 30 seconds, and allow the two layers to separate. Drain the lower layer to a 50-ml. conical flask until the ketone layer just reaches the top of the bore of the stopcock. Pour the ketone into a clean 100-ml. platinum dish. Repeat the extraction and add the second 5-ml. ketone extract t o the same dish. Evaporate the combined ketone extracts to dryness on a hot water bath under an air jet. Add 0.25 ml. of perchloric acid plus 0.25 ml. of nitric acid and heat on a low temperature hot plate until copious fumes of perchloric acid are being evolved. Finally add 0.25 ml. of nitric acid and evaporate to complete dryness. Cool, add 1 ml. of hydrofluoric acid (1 99), stir with a platinum rod, and warm to dissolve the residue. [If removal of chromium has not been complete, add a drop of 30% hydrogen peroxide, evaporate to dryness under an air jet, and repeat the solution in 1 ml. of hydrofluoric acid (1 99).] Continue as directed in Preparation of Calibration Curve.
Table
DISCUSSION
Masking agents such as thioglycolic acid, tiron, and hydrogen peroxide cannot be used in the above method because they complex tantalum too strongly. In contrast, the complexing action of EDTA on tantalum is much less than it is on most other metals. By arranging to make the color development a t a low pH and in the presence of an excess of EDTA the interference in the photometric phenylfluorone determination of tantalum can be markedly restricted. In fact tests have shown that, of the metals listed in Table I, only germanium, tellurium, titanium, sexivalent chromium, trivalent antimony, and niobium interfere. The extent of this interference can be seen in Table 11. To obtain these data an aliquot of standard tantalum solution plus an aliquot of a standard solution of the metal being tested was evaporated to dryness in a platinum dish and then treated as directed in Preparation of Calibration Curve. Strangely, the interference of tellurium, titanium, and niobium appears to be greater in the presence of tantalum than in its absence. The interference shown in Table I1 can be eliminated by isolating the tantalum by the methyl isobutyl ketone
Specificity of the Proposed Method for Tantalum
Metals Added, 100 y Ta, Na, K, Cs, Rb, Li, La Ta, Gal Hg, Au, Bi, Pt, Rh Ta, P, W, Re, Mo, Si, Se Ta, Fe, Mn, Pr, Hf, Th, Ru Ta, Al, V, Co, Ir, Zr, Cu Ta, Zn, Pb, T1, U, Os, In Tal Sn, Be, Os, Cd, Xi, Cr(II1) Ta, Ce, Nb, Ba, Cn, Mg, B, Y Ta, Ag, Pd, Sc, Sr, Sm Ta, Ti, Te, Nb, Gel Sb(II1) Ta, Nb (500 y ) Tal Ti (500 y) Ta, Te (500 y ) Tal Ge (500 y ) Ta, Sb(II1) (500 y ) Ta, Sb(V) (500 y) Ta, Cr(V1) (500 7 ) Table
Tantalum Found, 98 98
100
99
100
99
100
98 99
100 101
98 98
100 98
99
100
II. Interference in Photometric Determination of Tantalum
Metals Added, 100 y Tantalum Found, y Ge Ta 350
+
+
+
I.
Nb 0
+ Ta
1000 y of Nb
13T"
+ 100 y of Ta used.
solvent extraction method before attempting its determination. About 92% of the tantalum can be recovered with a single extraction or about 98% with a double extraction. Small amounts of certain metals accompany the tantalum but there appears to be very little extraction of the six interfering metals with the exception of sexivalent chromium. Extraction of the latter can be virtually eliminated by previous reduction to the trivalent state. By using the ketone extraction, the tantalum determination can be made completely specific as shown in Table I. To obtain these data, an aliquot of standard tantalum solution plus aliquots of standard solutions of several other metals were evaporated to dryness in a platinum dish and then analyzed for tantalum as directed in Analysis of Sample. If the sample to be analyzed for tantalum contains more than about 0.5 mg. of such severely interfering metals as germanium, tellurium, or titanium it may be advisable to make an acid wash of the combined ketone extracts by shaking for 30 seconds with 5 ml. of the hydrofluoric-hydrochloric acid solution, allowing to settle, and then discarding the lower layer. An alternative procedure, in the analysis of samples containing appreciable amounts of germanium, would be to expel traces of this metal, that may have accompanied the tantalum in the extraction, VOL. 31, NO. 5, MAY 1959
905
by adding 1 ml. of hydrochloric acid to the dry residue and evaporating to dryness just before the color development. The optimum wave length for the photometric determination of tantalum is 530 mp, since the relative absorption of the colored tantalum compound versus the reagent background is maximum a t this wave length. The calibration curve obtained a t 530 mp is linear and transmittances ranging from 85%
producible results are to be obtained. When such control is maintained, satisfactory quantitative determination of tantalum is possible.
for the reagent blank to 15% for 120 micrograms of tantalum are obtained when a 1-em. absorption cell is used. The intensity of the color of the tantalum-phenylfluorone solutions increases slowly with time even after a 30-minute color development. The rate of color development is influenced by such factors as the pH and the concentration of fluoride, EDTA, buffer, and phenylfluorone. All these variables must be closely controlled if re-
LITERATURE CITED
(1) Luke, C. L., Campbell, M. E., ANAL. CHEY.28, 1273 (1966). (2) Theodore, ill. L., Zbid., 30, 465 (1958).
RECEIVED for review August 25, 1958. hccepted December 9, 1958.
Hydrocarbon Compound-Type Analysis of Automobile Exhaust Gases by Mass Spectrometry DALE M. COULSON Department of Chemistry, Stanford Research Institute, Menlo Park, Calif.
b A method of hydrocarbon-type analysis of gaseous mixtures such as automobile exhaust gases is based on mass spectrometry. Mercuric perchlorate and perchloric acid on granular firebrick were used to remove olefins and acetylenes in the gas phase. The olefinic components were removed by taking an aliquot of the gaseous sample into the mass spectrometer through an absorption column packed with mercuric perchlorate-treated firebrick. By comparing this spectrum with that of an untreated sample, a clean separation of the spectra of paraffinic and olefinic compounds could b e made. The results are interpreted in terms of the hydrocarbon types-paraffins, cycloparaffins, mono-olefins, acetylenes, and cycloolefins, and aromatics.
M
has been SUCcessfully applied to the analysis of complex mixtures of hydrocarbons, including gasoline. Brown’s (1) comprehensive treatment of this subject, included a rather complete bibliography. Walker and O’Hara applied mass spectrometry to the analysis of automobile exhaust gases (4). Success depends on whether each component or type of compound yields a significantly different pattern from the others present in the mixture. I n Brown’s treatment, compounds of general classes were grouped together, giving four major compound types which were determined as groups of compounds. These are aliphatic paraffins, mono-olefins and cycloparaffins, aromatics, and “coda” (consisting of cyclomono-olefins, diolefins, and acetylenes). The purpose of this work was to develop a method for distinguishing be906
ASS SPECTROSIETRY
ANALYTICAL CHEMISTRY
COLUMN P A C K I NG\ G-ASS S:REW‘\
DISK CONTAINING /SMALL
HOLES
k
T 3 MASS
__f
FROM SAMPLE CONTA I NE R
\ORIFICE
0
1
2
3
Figure 1. OlefinI absorption tu b e
4
INCHES
tween cycloparaffins and mono-olefins in gaseous mixtures by mass spectrometry. The mass spectral patterns are too similar to allow interpretation of the spectra in terms of these two types of compounds. Brown (1) suggested bromination or nitrosation for differentiating between mono-olefins and cycloparaffins in the case of condensed samples. An attempt to adapt a bromination procedure to the analysis of automobile exhaust gases failed because part of the paraffins, and all of the olefins, were lost in contacting the gases with an aqueous bromine solution. The work of Young, Pratt, and Ride (5),in which aqueous mercuric perchlorate solution mas used to trap ethylene produced by ripening fruit, suggested a solution. Mercuric perchlorate is capable of holding ethylene and other olefins through n-bonding of the mercury with the unsaturated bond of the olefin. It was correctly assumed that solid mercuric perchlorate might serve equally well, Mercuric perchlorate and perchloric acid on the surface of 40- to 60-mesh Johns-Manville firebrick effectively remove olefins from a gaseous hydrocarbon mixture. This method, combined with mass spectroscopy, makes it possible to
differentiate between olefins and cycloparaffins. EXPERIMENTAL
Several synthetic mixtures containing a limited number of saturated and unsaturated aliphatic hydrocarbons and sufficient air to give hydrocarbon concentrations similar to the total hydrocarbon concentration present in automobile exhaust gases were prepared in 1-liter stainless steel cylinders. These cylinders were maintained a t 100” C. throughout the experiments. The mass spectral pattern for an aliquot of each mixture was quantitatively in agreement with that expected on the basis of the individual patterns for these components. A Consolidated Electrodynamics Corp. Model 21-401 mass spectrometer, rrhich measures m/e+ values up to 115, was used. A second aliquot of the synthetic mixture was introduced into the mass spectrometer gas handling system through ,a 40- to 60-mesh mercuric perchlorate-treated Johns-Manville firebrick column a t various temperatures a t the rate of 110 cc. per minute. This olefin absorption column is shown in Figure 1. The column packing was 15 mm. in length and 7 mm. in diameter, weighed approximately 0.2 gram
