Determination of Carbon Disulfide in Air By Means of Copper and Diethylamine in 2-Methoxyethanol FREDERICK F. h)IOREHEAD, American Viscose Corporation, Roanoke, Va.
T
HE development of a satisfactory micromethod for the
determination of carbon disulfide in air has been especially desirable for use in the viscose rayon industry, where the problems involved are not only those of hygiene, but also of the efficiency and economy of ventilating systems, the detection of leaks, etc. The chief limitations of both volumetric and colorimetric modifications of the generally accepted xanthate method (4) for carbon disulfide in gas mixtures are that they require the aspiration of such large volumes of air (56,000 ml., 2 cubic feet, or more) for the extremely small concentrations usually found in practice, and that excessively large blank corrections are necessary.
a new absorption tube which can easily be constructed by the average amateur glass blon-er was designed to incorporate the following desirable features : small rolume; pro\+ sion for intimate contact between gas and liquid; rery low resistance to the flow of gas; and ease of complete washing with small volumes of liquid. A small bulb, 10 to 15 mm. in diameter, is blown about 2 em. from the end of a 12- t o 16-cm. length of 1-mm. Pyrex capillary tubing; and the other end is sealed t o a 6- to 7-em. piece of 10mm. Pyrex tubing (Figure 1). Small indentations are placed in the tubing near the joint, to prevent the filling of 3-mm. solid glass beads from dropping dovn and sealing the capillary. Xext, a 3- to 4-cm. length of 7-mm. Pyrex tubing is sealed on, the 10mm. section is nearly filled with beads, and the joint between the two is constricted t o prevent them from falling out when the tube is inverted. Finally, the capillary tubing is bent t o an angle of 60" near the joint for ease in washing, and to some convenient obtuse angle near the other end, as shoivn in Figure 1. The outlet tube may also be bent to an angle if desired. This single absorption tube may be used alone in many cases, or in connection with a purification train. Resistoflex tubing, obtainable from the Resistoflex Corporation, Belleville, If. J., is a satisfactory substitute for ground-glass connections. Figure 2 shows a convenient arrangement for rapid sampling of small volumes of air. A Klett colorimeter was used in this investigation, the 2-ml. microcups being employed.
Reagents 2-Methoxyethanol, obtained from the Carbide and Carbon Chemicals Corporation under the name of methyl Cellosolve. If not colorless, it may be rendered eo by distillation in glass. Diethylamine, 1 per cent by volume in 2-methoxyethanol, obtained from the Eastman Kodak Company. The product boiling at 55-56' C. n-as found to be satisfactory. Cupric acetate, 0.1 per cent by weight in 2-methoxyethanol. Cupric sulfate, 5 per cent by weight in water, for removal of hydrogen sulfide in the purification train. Lead acetate paper may be substituted. BCLB FIGCRE 1. NEWTYPEOF ABSORPTION The recently published procedures ( 1 , 2 , 3 , 6 , 7 ) based , upon the production of a yellom7 or golden-brown coloration by the action of carbon disulfide on diethylamine in the presence of copper ions, are considerably more sensitive and accurate than the xanthate methods, but the colors obtained in ethanol are rather unstable and subject to fading. However, the present author has discovered that the 2-methoxyethanol recently recommended by Winsor ( 8 ) as a reaction medium in the colorimetric thiocyanate method for iron is also ideal for the determination of carbon disulfide b y the copper-diethyldithiocarbamate reaction. The color obtained in this medium is not only more intense than that produced in ethanol, but is also stable for 24 or even 48 hours. Further, only comparatively small samples (100 to 1000 ml.) are necessary with this modification.
FIGCRE 2. METHOD FOR TAKING RAPID SAMPLES
Apparatus The absorption train first used in this investigation consisted of three Huff (5) five-bulb tubes bloKn from 6-mm. tubing, the first two being sealed together and the third attached by a ground-glass joint. This type proved satisfactory so long as the rate of aspiration did not exceed 5 ml. per minute; but in the course of the work it became necessary to sample a t the rate of 50 ml. per minute or more. Hence, 373
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TABLE I.
hALYSIS OF
KNOWNAIR-GASMIXTURES
Carbon Disulfide Taken Micrograms
Carbon Disulfide Found Micrograms
7.89 14.58 28.60
28,36
S 03 14.54
Difference Microgram 0.14
-0.04 -0.24
TABLE 11. ANALYSIS OF AIR SAMPLES ESCOUNTERED IN PRACTICE Carbon Disulfide Found Copper: Xanthate diethylamine method method Alicrograins .lficrogran~s
reason, i t is usually desirable to insert a drying tube in the train, even in the absence of hydrogen sulfide, which of course must be removed. Passage of large volumes of carbon disulfide-free air through the mixed reagent caused no blank, nor did it affect the intensity of color produced by the addition of a known amount of carbon disulfide. 30 I
I
1
I
Difference Microgram
Sulfuric acid, c. P., concentrated, for the purification train. Other drying agents may be substituted. Carbon disulfide, c. P., redistilled, for the preparation of standards.
Experimental Procedure T h e n hydrogen sulfide is present, it must be removed by absorption in 5 per cent cupric sulfate solution, or by passing over lead acetate paper, since copper sulfide would othemise be precipitated in the copper-diethylamine reagent. The gas stream is then dried by sulfuric acid or other suitable desiccating agent; if hydrogen sulfide is absent, t h e entire purification train can often be omitted. The reaction tube itself should contain 1 1111. of the diethylamine reagent, plus 2 drops of the 0.1 per cent cupric acetate solution. To make a determination, a known volume of air is aspirated through the apparatus, followed by 100 ml. of carbon disulfidefree air when the purification train has been used, to sweep the latter free from carbon disulfide. Then the reaction mixture is rinsed into a 2-ml. calibrated flask and made up to the mark with 2-methoxyethanol. At the same time a suitable standard, containing 5 to 20 micrograms of carbon disulfide, is prepared, using the same quantities of reagents; and after 20 minutes, they are compared in the colorimeter. Typical Results Several milligram lots of carbon disulfide were weighed in sealed bulbs on a microbalance, and broken in a 12-liter bottle. After allowing sufficient time for the gas to diffuse through the bottle, samples were withdrawn and analyzed. The results in Table I show good agreement with the theoretical values, for the small amounts involved.
Discussion The reaction was found to be almost instantaneous alien used as directed. It was observed in a number of runs using the Huff ( 5 ) tubes on air containing small quantities of carbon disulfide that the yellow color mas produced only in the first bulb, and that there was practically no spray carried over into the second. K h e n ethanol was used as the reaction medium, i t w-as necessary to increase the number of tubes to take care of both the sprag carried over and the apparently slower rate of reaction. I n comparing the intensities of colors produced in etlianol and in 2-methoxyethanol, using 20 micrograms of carbon disulfide in each case, colorimeter readings r e r e 20.0 and 13.5 mm., respectively, showing an increase of 67.5 per cent in intensity for the latter. Standards containing 20 micrograms of carbon disulfide in 2-methoxyethanol matched similar freshly prepared standards even after 48 hours; longer standing produced some fading. The sensitivity of the reaction was not appreciably affected by as much as 20 per cent of water in the mixed reagent, but fading wa6 much more rapid in this case; for this
RATIOS
FICCRE 3. DETERNIN.4TION O F C A R B O S DISCLFIDE U n k n o u n set a t 20.0 mm., 2-ml. microcups used. Reading forstandard, micrograms of carbondisulfide: 3, 20: @, 10; t,5 . The most satisfactory range for this method proved to be from 1 to 30 micrograms, higher concentrations than these giving colors too dense for accurate comparison. The curves in Figure 3 for standards containing 5, 10, and 20 micrograms of carbon disulfide, respectively, show that Beer's law is obeyed satisfactorily for the entire range recommended in this paper. Proportional parts of these standards were taken, the unknom-n being placed in the colorimeter cup set a t 20.0 mm., anti then matched by the standard.
Summary The copper-diethylamine method for the determination of carbon disulfide has been made sufficiently sensitive for the determination of lo^ concentrations in reasonably small samples of air by the use of 2-methoxyethanol as the reaction medium. Very good agreement with Beer's law has heen shon n, and the results compare favorably with those obtained by the xanthate method when used on air. A new and very satisfactory type of absorption tube is described. The inrestigation is being continued with the object of improving the apparatus and technique, and of adapting it to the deterruination of copper.
Literature Cited (1) Cnllan, T , Henderson, J. R., and Stafford, J., J . SOC.Chem Ind., 51, 193-4T (1932). ( 2 ) Conn, L. IT., Johnson, 9.J., Trebler. H . A., and Karpenko, V . ,
ISD. ESG.CHEXI.,Anal. Ed., 7, 15-23 (1936). (31 Dept. Sei. Ind. Research, Leaflet 6, London, England, Stationery Office (1939). (4) Desy. G., PTOC. Am. Gas Assoc., 1927, 1440-1. (5) Huff, K.J., J . Am. Chem. SOC.,48, 81-7 (1926). (6) Snell, F. D., "Colorlmetrlc Methods of Analysis", New York, D. Van Nostrand Co., 1936. ( 7 ) Tisbler, N., IND. EXG.CHEM.,Anal. Ed., 4, 146 (1932). (8) Winsor, H. W., Ibid., 9, 453-5 (1937). PRESENTED before t h e Division of Microchemistry at t h e 97th Xeeting of t h e -4merican Chemical Society, Baltimore, M d .
