Artalyst, August, 1973, Vol. 98, 99. 585-592 585 A Modified Field Test for the Determination of Carbon Disulphide Vapour in Air BY E. C. HUNT, W. A. McNALLY AND A. F. SMITH (Department of Trade and Industry, Laboratory of the Government Chemist, Cornwall House, Stamford Street, London, SE1 9NQ) An improved and more sensitive method is described for the determination of carbon disulphide vapour in air a t concentrations up to 40 p.p.m. V/V. Carbon disulphide vapour is absorbed from a 500-ml sample of air into an ethanolic solution containing copper(I1) acetate, diethylamine and triethanol- amine. The yellow colour produced is compared visually with standard colours or measured spectrophotometrically. For field use, the apparatus is portable and simple to operate, and requires a working time of about 5 minutes per determination.THE field test currently in use by H.M. Factory Inspectorate for the determination of carbon disulphide vapour in air1 is basically the same as that which was first published in 1939 and is derived from a method2 originally published in 1932. The method is required for assessing the atmosphere within a factory and to give a rapid, approximate determination of concen- trations of carbon disulphide in the region of the threshold limit value, currently 20 p.p.m. V/V,3 in order to judge whether or not a hazard to health exists. (Threshold limit values refer to time-weighted concentrations in air for an 8-hour working day and a 40-hour working week, and represent conditions under which it is believed that nearly all workers may be repeatedly exposed without adverse effect on their health.Detailed conditions and exceptions are given in reference 3.) A re-examination of the method was undertaken for the following three reasons. (i) It was occasionally found that when the component solutions were mixed in the bubbler the absorption solution became turbid and its colour blue instead of remaining a clear, pale green. (ii) The volume of air to be sampled (2.5 litres) was of an inconvenient size; it was excessively large for the use of a rubber-bulb aspirator, which would require twenty aspira- tions, and too small to warrant the use of an electric pump and flow meter. The rubber-bulb aspirator was preferred because of its portability, and so an increase in sensitivity was sought in order to permit a reduction in the volume of air sampled.(iiz) The existing method was devised before threshold limit values for toxic substances in air were first compiled and it does not provide for a standard at the threshold limit value for carbon disulphide. A survey of published analytical methods disclosed no method that appeared suitable for adaptation as a replacement for the existing method, and modification of the latter seemed to afford the most profitable line of investigation. EXPERIMENTAL The current method requires the contaminated atmosphere to be passed through a bubbler containing 10 ml of ethanol, 2 ml of a 2 per cent. V/V solution of diethylamine in benzene and 2 ml of a 0.1 per cent. m/V solution of copper(I1) acetate in ethanol; the colour of the copper diethyldithiocarbamate formed is allowed to develop for 20 minutes.For use as a field method, the amount of carbon disulphide collected in the absorption solution is determined by visually comparing the colour formed in this solution with colour standards. The first steps taken to improve the sensitivity were to reduce the concentration of copper(I1) acetate in the absorption solution from 0.014 to 0.002 per cent. m/V, to eliminate the benzene by preparing the diethylamine solution in ethanol and to reduce the total volume of the absorption solution by adding only 6 ml of ethanol instead of 10 ml. These changes, and the evaluation of the colour by using a longer light path, produced a satisfactory increase n sensitivity, with the added advantage that the reagent blank was colourless instead of @ SAC; Crown Copyright Reserved.586 HUNT, MCNALLY AND SMITH: A MODIFIED FIELD TEST FOR [Amlyst, Vol.98 pale green. During the development of the method, colours were measured spectrophoto- metrically4 at 430 nm after allowing the colour to form for 20 minutes. The optical density was found to reach a maximum at this wavelength after about 2 minutes (Fig. 1) but the colour changed visibly from lemon yellow to amber during the subsequent 18 minutes. The absorption spectrum of the solution, recorded at intervals (Fig. l), showed initially a single peak with ix maximum at 440 nm. Within 5 minutes, the peak had shifted to 457 nrn and a shoulder had begun to appear at about 385 nm, which developed into a peak and increased in height for at least 30 minutes.The peak a t 457 nm reached a maximum during this time. 0.5 1 0.4 3 50 400 450 500 Wavelength/nm Fig. 1. Variation of the absorption spectrum with reaction time. Carbon disulphide (60 p g ) added to ethanol containing 0.002 per cent. m/V of copper(I1) acetate and 0.4 per cent. V / V of diethylamine. Re- action time: A, 1 ; B, 2 ; C, 5; D, 15; and E, 30 minutes EFFECT OF WATER- It was found, during tests with the current field method for determining carbon di-- sulphide, that the addition of a small amount of water to the absorption solution produced turbidity and a change in colour from pale green to pale blue. Application of the test under factory conditions, with possibly perfunctory washing and drying of the apparatus, could lead to retention of moisture, especially as sintered-glass bubblers are used.Similar effects were found with the modified absorption solution described above when water was added. The modified solution was prepared in absolute ethanol (maximum water content 0-5 per cent. V / V ) and contained no benzene. Small amounts of water were added to the ethanol used in preparing the reagent solutions in order to study the effect on colour in more detail. Absorption spectra recorded after the addition of 60 pg of carbon disulphide to the absorption solution, and allowing 30 minutes for reaction time, showed that as the water content increased, the peak at 385 nm was reduced and the main peak at 457 nm shifted to 435 nm. With additions of water to concentrations greater than 5 per cent.V/V, only the peak at 435 nm remained (Table I). At these levels of water concentration, the copper(I1) acetate solution deteriorated rapidly, turning dark brown and becoming turbid. Replacement of ethanol with butan-2-01 or 2-methoxyethanol has been recommended5 in order to eliminate this effect but was found to be unsatisfactory because of the formation of coloured reagent blanks that seriously impaired visual colour comparison. Other workers6y7 had added tri- ethanolamine to the absorption solution but, when it was added to the solution used in the current field method, the blank solution became blue in colour. However, a stable colour with an absorption maximum at 430 nm was obtained in the presence of carbon disulphide, which was not affected by additions of water in the range 1 to 10 per cent.V/V. With the modified absorption solution, which contained less copper(I1) acetate, the reagent blank wasAugust, 19731 THE DETERMINATION OF CARBON DISULPHIDE VAPOUR IN AIR TABLE I EFFECT OF VARIATION OF WATER CONTENT ON THE COLOUR 587 Carbon disulphide (60 pg) in 10 ml of ethanol containing 0.002 per cent. m/V of copper(I1) acetate and 0.4 per cent. V/V of diethylamine after colour development for 30 minutes Water content, Optical density per cent. V/ V Absorption maximumlnm (10-mm cells) 0.5 385 0.300 457 0-460 1.0 385 0.250 457 0.455 1.5 385 0.200 457 0.450 2.0 448 0.450 2.5 442 0.470 3.0 440 0.480 3.5 440 0-495 4.0 440 0.490 4.5 440 0.505 5.0 435 0.500 10.0 435 0.500 20.0 435 0.510 Optical densities a t 385 nm remained constant at 0-200 for water contents of 1-5 per cent.or more. reduced to an acceptable level without unduly affecting the sensitivity of the test. A con- centration of 1.0 per cent. V/V of triethanolamine in the absorption solution was chosen because, at this level, small errors in volume measurement, caused by the viscous character of the liquid, would not seriously affect the final colour or the sensitivity of the test (Table 11). With the incorporation of triethanolamine, all the reagents could be combined in a single solution that was stable for at least 1 month, and the more widely available industrial methylated spirit (water content about 5 per cent. V/V) could be used instead of absolute ethanol. TABLE I1 EFFECT OF ADDITION OF TRIETHANOLAMINE Carbon disulphide (60 pg) in m/V of copper(I1) acetate and 10 ml of 96 per cent.V/V ethanol containing 0.002 per cent. 0.4 per cent. V/V of diethylamine after colour development for 5 minutes Triethanolamine content, per cent. V/V 0 0.2 0.4 0.8 1.2 1.6 2.0 4.0 Optical density a t 430 nm (10-mm cells) 0.492 0.461 0.455 0.455 0.455 0-45.5 0.450 0.440 PREPARATION OF A STANDARD ATMOSPHERE- An atmosphere containing a known concentration of carbon disulphide was required to assess the efficiency of sampling and of the chemical reactions that took place during the application of the field method. The atmosphere was prepared dynamically by an injection - atomisation technique in which carbon disulphide was injected at a known rate into a metered air stream.Part of this atmosphere was diluted with a second metered air stream to give the required concentrations. (The standard atmosphere generator was designed to ensure homogeneity and was checked at several different concentrations by a chemical method other than the described field test and found to give reproducible results.) The generated atmos- phere was calibrated by collecting samples at the rate of 125 ml min-l for 8 minutes in three all- glass bubblers in series, each containing 10 ml of ethanolic potassium hydroxide solution (0.2 per cent. m/V). The xanthate formed in each bubbler was determined spectrophotometrically588 [Analyst, vol. 98 as its copper salt.* With atmospheres containing up to 40 p.p.m. V/V of carbon disulphide, no colour developed in the last bubbler.COLLECTION OF CARBON DISULPHIDE- The efficiency of absorption of carbon disulphide from air with the simple bubbler and absorption solution described in the Procedure was found to be 100, 94 and 89 per cent. at flow-rates of 50, 125 and 200 ml min-l, respectively, for atmospheric concentrations in the range 0 to 40 p.p.m. V/V. The effect of temperature on absorption efficiency was found to be small and was linear between values of 96 per cent. at 5 "C and 91 per cent. at 35 "C, at the prescribed flow-rate of 125 ml min-l. RELIABILITY OF REAGENTS- A comparison was made of reagents used in the test that were obtained from various manufacturers and of different batches from the same manufacturer. Negligible differences were found. HUNT, McNALLY AND SMITH: A MODIFIED FIELD TEST FOR INTERFERENCES- Hydrogen sulphide is the substance most likely to be found as an industrial co-con- taminant with carbon disulphide and is known to give a positive reaction with the proposed test.A hydrogen sulphide atmosphere, prepared by an injection technique, was stan- dardised by an iodimetric method. Samples of this atmosphere at concentrations of 10, 20 and 40 p.p.m. V/V were taken by the proposed field method and were found to give colours equivalent to 3, 5 and 10 p.p.m. of carbon disulphide, respectively. The current method for determining carbon disulphide in air1 recommends the use of filter-paper im- pregnated with lead acetate to remove hydrogen sulphide and this method, together with the use of similarly impregnated cotton-wool, was investigated for use with the revised test.The introduction of a filter into the sampling system considerably reduced the flow-rate and also the effective volume sampled when a rubber-bulb aspirator was used, hence it was essential that the flow-rate of the aspirator be adjusted before use, with both filter and bubbler in circuit. Once adjusted, no significant change in flow-rate was noted when the filter-paper was changed. Cotton-wool, however, gave variable flow-rates, depending on its packing density; consequently, its use as a hydrogen sulphide trap was abandoned. Samples of the standard hydrogen sulphide atmosphere at concentrations of 10, 20 and 40 p.p.m. V/V were taken by the proposed method with a pre-filter of impregnated paper.Colours equivalent to 1, 2 and 4 p.p.m. of carbon disulphide, respectively, were obtained by using Whatman No.1 filter-paper and 0, less than 0.5 and 1 p.p.m. by using Whatman 3MM paper; the latter was chosen as suitable for use in the test. By mixing the outputs from the two generators in suitable proportions, a mixed atmos- phere was obtained, which was sampled both with and without a pre-filter prepared from Whatman 3MM paper. The average results obtained are shown in Table 111. TABLE I11 INTERFERENCE EFFECT OF HYDROGEN SULPHIDE ON THE FIELD METHOD Tests with standard atmospheres with and without lead acetate filters Found by field test, p.p.m. V/V of carbon disulphide Atmospheric concentration, p.p.m. V / V Carbon disulphide Hydrogen sulphide With filter Without filter 22.5 0 22-5 22.5 0 8.7 0 2.3 22.5 8.7 22.5 24-8 A r A > r 1 PREPARATION OF COLOUR STANDARDS- Colour standards were prepared by adding aliquot portions of an ethanolic solution of carbon disulphide to the absorption solution, allowance being made for volume changes and the fact that only 94 per cent.of the carbon disulphide present in the atmosphere is collected under the test conditions. Once prepared, the standards were found to be stable for at least 4 hours, provided that they were kept in well stoppered tubes. Details of the preparationAugust, 19731 589 of these standards are given later. Results obtained when carbon disulphide atmospheres of known concentration were sampled by the proposed method are given in Table IV. The levels were assessed visually by using the colour standards and, more accurately, with a spectrophotometer.The optical densities of the solutions were measured at 430 nm and the carbon disulphide concentration was determined by reference to a prepared calibration graph. TABLE IV EVALUATION OF FIELD METHOD WITH STANDARD ATMOSPHERES THE DETERMINATION OF CARBON DISULPHIDE VAPOUR IN AIR Concentration of carbon disulphide, p.p.m. V/ V i- A > Found by field method c A 7 Present By visual comparison Spectrophotometrically 2.5 0 to 5 2.7 4.3 0 to 5 4.5 5-0 5+ 4.7 5.3 5+ 5.0 5-0 5 4.7 4.3 5 5.0 10.0 10 9.8 10.0 10 + 10.3 10.7 10 - 10.0 10-7 10 + 10.7 16-0 10 to 20 15-3 19-7 20 20.0 20.0 20 20.0 21.0 20 + 19.9 29.8 30 30.0 29.7 30 30.0 40.0 40 + 39.3 40.3 40 41.3 Plus or minus symbols indicate values slightly greater than, or slightly less than, that of the nearest colour standard.FIELD METHOD FOR THE DETERMINATION OF CARBON DISULPHIDE VAPOUR APPARATUS- Glass bubbler-As shown in Fig. 2. -25 i.d. Fig. 2. Diagram of bubbler. (All measurements are in millimetres) IN AIR590 HUNT, MCNALLY AND SMITH: A MODIFIED FIELD TEST FOR [Analyst, Vol. 98 Aspivator-A rubber bulb or other device capable of drawing air through the apparatus at the rate of 125 ml min-l. Colour comparison tubes-Flat-bottomed glass tubes of 10 mm i.d., calibrated with a mark at a height of 50mm. Filter-paper holdev. REAGENTS- Reagents should be of analytical-reagent grade when possible. Absorption solution-Dissolve 0.01 g of copper(I1) acetate monohydrate in a small amount of cold ethanol and transfer the solution into a 500-ml calibrated flask with about 100 ml of ethanol (industrial methylated spirit can be used instead of ethanol if desired).Add, from a measuring cylinder, 5 ml of triethanolamine and wash any residue in the cylinder into the flask with ethanol. Swirl the contents of the flask until the triethanolamine has completely dissolved. Add 2 ml of diethylamine and dilute to 500 ml with ethanol. This solution can be used for 1 month if stored at temperatures below 30 "C in tightly stoppered bottles. Lead acetate solzttiofz-Dissolve 10 g of lead acetate trihydrate in 90 ml of water. Add 5 ml of glacial acetic acid and 10 ml of glycerol to the solution and mix well. Lead acetate $apers--Immerse strips of Whatman 3MM chromatographic paper, 20 mm wide and 100 mm long, vertically for 1 minute in the lead acetate solution contained in a 100-ml measuring cylinder.Remove the papers and allow the excess of liquid to drain. Suspend the papers vertically and allow them to dry at room temperature in an atmosphere free from hydrogen sulphide. When dry, remove and discard portions 25 rnrn in length from the top and bottom of each strip. Store the prepared papers in stoppered, wide-necked, dark-glass bottles to protect them from light and air. Use within 14 days of preparatjon. PREPARATION OF COLOUR STANDARDS- Caybon disulphide solutiow-Dilute 1 ml of carbon disulphide to 100 ml with ethanol (or industrial methylated spirit). Dilute 1 ml of this solution to 250 ml with ethanol. This solution can be used for 1 week if stored below 30 "C in a well stoppered bottle.Prepare four standards representing 0, 10, 20 and 40 p.p.m. V/V of carbon disulphide in air (0, 30, 60 and 120 mg 111-3) by adding 0, 0.30, 0-60 and 1-20 ml of the carbon disulphide solution to 10ml of the absorbing solution. Allow the colours to develop for 10 minutes before carrying out colour comparisons. Some approximations are involved in these standards for the visual determination, but allowance is made for volume changes and for the 94 per cent. efficiency of absorption in the bubblers. An additional standard representing 5 p.p.m. V/V (0.15 ml) can be included if required. The colour standards are stable for about 4 hours if kept in well stoppered tubes. As an alternative, a series of permanent glass standards in a comparator disc, obtainable from Tintometer Ltd., Salisbury (Catalogue No.6/56), can be used in conjunction with a Lovibond 1000 Comparator with a vertical viewing attachment. PROCEDURE- In a carbon disulphide free atmosphere, transfer by means of a pipette 10 ml of the absorption solution into the glass bubbler. Insert the inlet tube and attach the aspirator. Transfer the apparatus to the sampling site and collect 500 ml of the atmosphere. Remove the apparatus to an uncontaminated area and, 10 minutes after collection, transfer the solution into a colour comparison tube, filling the tube up to the calibration mark, and compare its colour with those of the colour standards by viewing downwards through the 50-mm depth of the liquids against a white background in daylight.If the presence of hydrogen sulphide is suspected, connect a suitable paper holder containing a lead acetate paper to the inlet tube of the bubbler. Re-adjust the aspirator, if necessary, so as to sample 125 ml in 1 minute; the resistance of the paper may reduce the volume of air sampled if a rubber-bulb aspirator is used. DISCUSSION AND RESULTS Both the turbidity and change of hue found occasionally with the current Factory Inspec- torate method,l and the change in colour with time observed with the first modificationsAugust, 19731 59 1 to this method, appear to have resulted from the formation of hydrolysed copper species in the solution. The addition of triethanolamine, which formed a stable ammine-type complex, overcame this effect and imparted a much greater tolerance to the presence of water in the absorption solution.An added advantage for field use was that this solution could be prepared and transported as a single reagent instead of the two reagent solutions and additional ethanol that were previously required. The method is capable of giving more accurate results if a spectrophotometer is used and optical densities are measured at 430nm in 10-mm cells. A calibration graph can be prepared for use with atmospheres containing 0 to 40 p.p.m. V/V by adding volumes of 0 to 1-20ml of the carbon disulphide solution to 10-ml calibrated flasks, diluting to the mark with absorption solution and measuring the optical densities after 10 minutes. Two bubblers in series should be used to ensure complete collection of carbon disulphide.In calculating the results, an atmospheric concentration of 20 p.p.m. V/V of carbon disulphide can be taken as equivalent to 62.2 pg 1-1 at 25 “C. One sample of each pair was absorbed in ethanol and returned to the laboratory for spectrophoto- metric determination of carbon disulphide by the xanthate method. The results are shown in Table V. Some of the samples were taken in positions that were not typical of a working environment in order to cover a wide range of atmospheric concentrations and provide a valid test for the method. None of the areas tested that might be occupied by workers had atmos- pheric concentrations of carbon disulphide greater than the threshold limit value3 of 20 p.p.m. V/V.Two samples (not shown in Table V) were taken in the factory in areas where hydrogen sulphide was known to be present. The field testg for hydrogen sulphide showed the presence of 5 and 8 p.p.m. V/V of this gas, which had little effect upon the colours produced by the carbon disulphide test. The use of lead acetate paper reduced the intensity of colour produced in each instance but the evaluation of the atmosphere remained the same, both with and with- out the treated paper, in relation to the nearest visual colour standard because of the low level of interference (approximately one tenth of the threshold limit value) at these concentrations. It was noted that, although the factory was pervaded by a characteristic “sulphur” odour, neither carbon disulphide nor hydrogen sulphide was detected by its odour, despite the fact that the field tests showed one or both to be present.THE DETERMINATION OF CARBON DISULPHIDE VAPOWR IN AIR Tests were conducted a t a viscose factory where duplicate samples were taken. TABLE V TEST OF THE FIELD METHOD AT A FACTORY Hydrogen sulphide, I A > Carbon disulphide concentration, p.p.m. V / V , by Sample p.p.m. V/V xanthate method field method 1 0 2 0 3 0 4 < 2 5 <2 6 0 2.6 4.6 6.4 22.4 25 160 o+ 20 to 40 (25) 0 to 5 (5-) 5 20 to 40 (20f) > 80 Figures in parentheses indicate visually estimated values. Plus or minus symbols indicate values slightly greater than, or slightly less For sample 6, 250 rnl of atmosphere were taken. than, that of the nearest colour standard. The sensitivity of the method was improved by reducing the concentration of copper(I1) acetate in the absorption solution, which gave a colourless reagent blank, and by increasing the path length of light used in viewing the colours.The stability of the absorption solution was improved by the addition of triethanolamine. The results shown in Tables IV and V show that the modified method is an effective replacement for the earlier method. This work was undertaken on behalf of the Department of Employment Committee on Tests for Toxic Substances in Air. The authors are indebted to the Government Chemist for permission to publish this paper, and to H.M. Factory Inspectorate for arranging the field tests.592 HUNT, McNALLY AND SMITH REFERENCES Department of Employment, “Methods for the Detection of Toxic Substances in Air, Booklet No. Tischler, N., Ind. Engng Chem. Analyt. Edn, 1932, 4, 146. Department of Employment, “Threshold Limit Values for 1971,” Technical Data Note 2/71, Sonnenschein, W., and Schafer, K., 2. analyt. Chem., 1953, 140, 15. Brown, E. G., Analyst, 1952, 77, 211. Viles, F. J., J . I n d . Hyg. Toxicol., 1940, 22, 188. Vasak, V., in Brieger, H., and Teisinger, J., Editors, “Toxicology of Carbon Disulphide (Inter- Jacobs, M. B., “The Analytical Chemistry of Industrial Poisons, Hazards and Solvents,” Second Department of Employment, “Methods for the Detection of Toxic Substances in Air, Booklet Received January 18th, 1973 Accepted March 2nd, 1973 6, Carbon Disulphide Vapour,” H.M. Stationery Office, London, 1968. H.M. Factory Inspectorate, London, 197 1. national Symposium),” Excerpta Medica Foundation, London, 1967, p. 15. Edition, Interscience Publishers Ltd., London, 1949, p. 334. No. 1, Hydrogen Sulphide,” H.M. Stationery Office, London, 1969. 1. 2. 3. 4. 5. 6. 7. 8. 9.