Table IV. Analysis of NBS and BCS Standard Samples NO.
Sample
67 Manganese steel (NBS) 117 Ferrotitanium (NBS) Steel (NBS) 132 Cr-V steel (BCS) 224 High speed (BCS) 241/1 a Average of 4 determinations.
New
method0
0.17-0.19 0.05-0.08 1.60-1.68 0.240 1.570
0.186 0.062 1.695 0.241 1.568
Table IV show that vanadium can be determined precisely and accurately.
021
0 0
Standard value vanadium
2.0
6.0
4.0
8.0
1
MOLES LIGAND PER MOLE VANADIUM
Figure 3. Mole ratio method
Table 111. Analytical Data on Extraction of Vanadium(V) Std dev
Vanadium(V),
(6 deter-
u g / 2 5 m l of
Vanadium(V)
chloroform
found, u g
Error
minations)
5 10 20 50 100 2 00
5.01 9.99 20.00 50.00 99.98 200.03
io.01 -0.01 0.00
io,01
0.00 -0.02 +0.03
10.02 10.02 10.01 10.01 10.03
Mn2+(30 mg), Zn2+(25 mg), Pb2+(30 mg), Ni2+(25 mg), M004~-(10 mg), u0z2-(25 mg), wo42-(15 mg), Ti3+(25 mg), A13+(30 mg), Ti4+(15 mg), Zr4+(30 mg), and 0s6+(60 mg). The complexing ions such as citrate, tartrate, phosphate, and fluoride had no effect on extraction and determination of vanadium. The analytical data on extraction of vanadium(V) in the presence of all the above diverse ions are given in Table 111. Determination of Vanadium in Steel. T o test the reliability of the method, 5 samples from the U S . National Bureau of Standards and the Bureau of Analyzed Samples Ltd. were analyzed for vanadium. The results presented in
ACKNOWLEDGMENT The author expresses his deep sense of gratitude to A. B. Biswas, Department of Chemistry, Indian Institute of Technology, Powai, Bombay 400 076 for his sustained interest in the execution of this work and his invaluable criticism.
LITERATURE CITED (1)G. A. Brydon and D. E. Ryan, Anal. Chim. Acta, 35, 190 (1966). (2) U. Priyadarshini and S. G. Tandon, Chem. hd. (London), 931 (1960). (3)D. E. Ryan, Analyst(London), 85,569 (1960). (4)U. Priyadarshini and S. G. Tandon, Anal. Chem., 33, 435 (1961). (5) U. Priyadarshini and S. G. Tandon, Analyst, (London). 88, 379 (1961). (6)D. C. Bhura and S. G. Tandon, Anal. Chim. Acta, 53, 379 (1971). (7)D. C. Bhura and S. G. Tandon, lndian J. Chem., 8, 1036 (1970). (8)J. P. Shukla and S. G. Tandon, J. lndian Chem. SOC.,49,83 (1972). (9)R. M. Cassidy and D. E. Ryan, Can. J. Chem., 46,327 (1967). (10)V. C. Bass and J. H. Yoe, Anal. Chlm. Acta, 35, 337 (1967). (11) A. K. Majumdar and G. Das, J. indlan Chem. SOC.,42, 189 (1965). (12)W. M. Wise and W. W. Brandt, Anal. Chem., 27, 1392 (1955). (13)S.G. Tandon, and S.C. Bhattacharyya, Anal. Chem.. 33, 1267 (1961). (14)A. S.Bhaduri and P. Ray, Z.Anal. Chem., 151, 109 (1956). (15)A. K. Majumdar and G. Das, Anal. Chlm. Acta, 31, 147 (1964). (16)R. L. Dutta, J. lndian Chem. SOC.,35,243 (1958). (17)U. Priyadarshini and S.G. Tandon, J. lndian Chem. Soc., in press. (18)V. K. Gupta and S.G. Tandon, J. lndian Chem. Soc., in press. (19)Y. K. Agrawal, Anal. Lett., 5, 863 (1972). (20) R. L. Dutta, J. lndian Chem. Soc., 36,285 (1959). (21)Y. K. Agrawal and S. G. Tandon, J. Chem. Eng. Data, 16,495 (1971). (22)W. F. Hillebrand, G. E. F. Lundel. H. A. Bright, and J. I. Hoffman, "Applied Inorganic Analysis," 2nd ed., Wiley, New York, N.Y.. 1953. (23)E. B. Sandell. "Colorimetric Determination of Traces of Metals", 3rd ed.. Interscience, New York, N.Y., 1959. (24)W. C. Vosburgh and G. R. Cooper, J. Am. Chem. Soc., 63,437 (1941).
RECEIVEDfor review October 11, 1974. Accepted January 21, 1975. A Senior Fellowship was awarded by C.S.I.R., New Delhi.
Determination of Carbon Disulfide in Industrial Atmospheres by an Extraction-Atomic Absorption Method B. M. Kneebone and Henry Freiser Chemistry Department, University of Arizona, Tucson, AZ 8572 1
The accurate measurement of ambient carbon disulfide vapor concentrations in industrial atmospheres, such as those in viscose fiber plants, is necessary to protect the health of workers, as required in the Occupational Safety and Health Act of 1970, Public Law 91-596. Among the deleterious effects of chronic CS2 intoxication are vitamin B6 deficiency, depletion of levels of essential trace metals such as Cu and Zn, and intensification of the development of atherosclerosis ( I , 2). 942
ANALYTICAL CHEMISTRY, VOL. 47, NO. 6, MAY 1975
The current methodology includes gas-liquid chromatography of samples collected on charcoal and desorbed with toluene or benzene ( 3 ) or the classical spectrophotometric determination of copper diethyldithiocarbamate formed by the absorption of CS2 in scrubbers containing diethylamine, triethanolamine and cupric acetate (4-7). Truhaut et al. (8) used diethanolamine as described by Cullen (9) and designed a portable apparatus to be worn by workers which collects CS2 vapors on activated charcoal.
T h e CS2 was desorbed by shaking t h e charcoal with toluene for 24 hours a n d determining by t h e formation of N,N-bis(P-
hydroxy-ethy1)dithiocarbamate. T h e sensitivity of these methods is usually in t h e region of 5-50 pg CS2. T h e current NIOSH detection limit is 6 pg/1. of air, which is 0.1 of t h e ACGIH threshold limit value (IO). T h e minimum contaminant-in-air concentration which NIOSH strives t o measure is 0.1 times t h e TLV. This study presents two new methods of CS2 determination, a potentiometric method based on t h e reaction of CS2 with pyrrolidine t o form t h e dithiocarbamate (PDTC) and its subsequent reaction with Cu t o form a chelate. T h e disappearance of Cu2+ is monitored with a solid-state Cu electrode. T h e second method is based on t h e same reaction, b u t t h e chelate is extracted into isoamyl acetate a n d determined directly via atomic absorption (AA). T h e detection limit of t h e two methods presented here is 7.0 pg CSZ/sample, although this is not t h e minimum which can be attained for t h e AA method. This value was sufficient for the range of samples which were submitted by NIOSH. T h e sensitivity can be improved at least fivefold by reducing t h e volume of t h e eFtracting solvent to 2.0 ml a n d extended even further by using a n atomic absorption spectrophotometer with greater sensitivity.
EXPERIMENTAL Apparatus. All potentiometric measurements were made with an Orion research Model 70l/digital pH meter using an Orion 9429 cupric ion selective electrode in conjunction with a 90-01 single junction reference electrode. A Perkin-Elmer 303 Atomic Absorption Spectrophotometer fitted with a Cu hollow cathode lamp was used for the AA measurements. Reagents. All reagents used were ACS Analytical Reagent grade. The pyrrolidine was freshly distilled weekly and stored under nitrogen. The isoamyl acetate was also redistilled weekly and stored tightly capped. Water was deionized and distilled. Procedures. Potentiometric Method. To a 25.0-ml aqueous (pH adjusted to 2.0 w/HCl) solution in a 100-ml beaker that is 10-3M in pyrrolidine, 1.00 X 10-4M in CuSO4, and usually between and 2 X 10-4M in CS:!, 25.0 ml of chloroform which has been presaturated with water were added. The solution was stirred rapidly for 5 min with a magnetic stirrer. The phases were allowed to separate, then the lower phase was removed. The Cu2+ concentration in the aqueous phase was measured with the Cu electrode. A calibration curved was prepared by treating a series of Cu solutions in the same manner. Determination of p H Range. A series of titrations was performed to determine the optimum pH range. A solution of 10-3M CuSO4 was titrated with 0.05M HC1 and monitored simultaneously with a glass and a Cu electrode vs. a single-junction reference electrode. This procedure was repeated with an identical solution which was additionally made 3 X 10-3M pyrrolidine dithiocarbamate. To this solution 25.0 ml of water-saturated chloroform was added. The initial pH was 10.0. The chelate was extracted into the chloroform phase by rapid magnetic stirring. After phase separation, a measurement of [Cu2+] and pH was made in the aqueous phase. This procedure was repeated after each addition of HC1. Atomic Absorption Method. To a 10.0 ml solution 10-2M in pyrrolidine and 10-3M in CuSO4, an amount of CS:! between 5-100 pg was added. The pH was adjusted to 2.0-2.5 with HCI. The solution was shaken with 10.0 ml of isoamyl acetate on a mechanical shaker for 5 min. The phases were separated and the aqueous phase discarded. The absorbance of the copper chelate was measured in an airacetylene flame. Determination of Desorption Efficiency of Various Soluents. CS2, 1.0 gg, was injected with a Hamilton syringe into the primary portion of blank charcoal-containing organic vapor sampling tubes (Mine Safety Appliances Co., Part No. 459004). The tubes were tightly capped and allowed to equilibrate undisturbed at room temperature for 24 hours. The charcoal from each section, A and B, was emptied into 40-ml vials, 10.0 ml of the solvent of interest
Table I. Potentiometric Determination of CS2 CCS'I
1.0 x 10-5
3.0 x 1 0 ' 5 5.0 x 1 0 ' 5
[ C ~ ' + I measures
9.2 x 10-5
8.1 x 1 0 ' 5 7.9 x 10-5 7.0 x 1 0 ' 5 6.2 x 10-5 1.0 x 10-4 5.3 x 10-5 aInitia1 [Cuz+]= lO-*M.
C C ~ ' + I theoretical
9.5 8.5 7.5 6.5 5.0
x x x x x
10'5 10'5 10-5 10-5 10-5
~rror,%
3.2 4.7 5.3 4.6 6.0
was added, and the mixture was shaken on a mechanical shaker for 30 min. After the charcoal granules had settled to the bottoms of the vials, the analysis was performed as described in the above paragraph. Analysis of NIOSH Samples. A set of organic vapor sampling tubes containing activated coconut charcoal in two sections, 100 mg in the trapping section and 50 mg in the backup section, was received. The two sections were separated by a piece of foam and a plug of glass wool was at the inlet end of the tube. A note by Kupel and White (11) gives further specifications. The sample tubes had been injected with amounts of CSz varying from 0.10 to 1.0 pl, which corresponds to a range of 1.65 X t o 1.65 X 10-3M when dissolved in 10.0 ml of organic phase. The charcoal from each section of the tubes was emptied into 40-ml vials and 10.0 ml of 0.01M pyrrolidine and 10.0 ml of solvent were added. The vials were capped and placed on a shaker for 30 min, after which time 1.0 ml of 0.01M CuSO4 was added and the vials shaken again for 10 min. The analyses were performed as described above. A set of standards was prepared by injecting the same volumes of CS2 into the primary section (A) of blank tubes and allowing them to equilibrate for 24 hours. They were then analyzed by the described atomic absorption procedure. A set of solutions of ammonium pyrrolidine dithiocarbamate (APDTC) containing the same amount of Cu was prepared for use as simulated CS2 standards.
RESULTS AND DISCUSSION Potentiometric Method. Titration of t h e Cu-PDTC chelate with HC1 showed t h a t t h e complex decomposes below pH 1.5. Hydroxide complex formation begins between p H 4-5 under t h e experimental conditions. A p H value of 2 was chosen because it could be easily attained with HC1. Experimental difficulties were encountered when i t was decided initially to use diethylamine to combine with CS2, as is common in t h e spectrophotometric methods. T h e diethyldithiocarbamate was very unstable in t h e acid solution, which was necessary t o prevent formation of Cu(OH)2, and decomposed during t h e measurements. According t o Scharfe e t al. (12),pyrrolidine DTC forms complexes of t h e same degree of stability as t h e widely used diethyl DTC. However, at t h e low p H of 1.0, pyrrolidine DTC has a t 1 / 2 = 30 min, while diethyl DTC has a t l l z = 7.5 sec for decomposition. T h e pyrrolidine was found t o be quite satisfactory since the procedure took no longer t h a n 15-20 min. An a t t e m p t was made t o measure t h e Cu concentration in t h e aqueous solution in the presence of Cu(PDTC)2, but t h e chelate precipitates and adheres t o t h e surface of t h e electrodes, making the response erratic and unstable. Extraction of t h e chelate into chloroform before measuring Cu in t h e aqueous phase removed t h e interference. T h e results in Table I show t h a t t h e average error in a carefully controlled CS2 determination is about 5% when using t h e concentrations of Cu a n d CS2 shown. T h e precision of replicate measurements was f3%. T h e limit of' detection of 7 pg CS2 corresponds t o a 0.3-mV change which is attainable only with very careful bracketing of t h e sample with standards. [Note: 7 pg C&/sample corresponds to [ C U 2 + ] = 9 x lo-%]. AA Method. T h e results in Table I1 show t h e advantage ANALYTICAL CHEMISTRY, VOL. 47, NO. 6, MAY 1975
943
~
~~
~~~~
~~~
~
~
Table IV. CS2 Assays of NIOSH Sample Tubes
Table 11. AA Determination of C S z a Absorbance [CS*I
Sample
1.0 x 0.0079 0.0218 3.0 X 5.0 X 0.0448 7.0 X 0.0655 1.0 x 0.0888 0.2011 2.0 x 10-4 Slope 1030 i 30 Intercept -0.007 k 0.003 Initial [CUI = 10-4M.
CSz found DTC Std
0.0078 0.0216 0.0454 0.0646 0.0903 0.2043 1040 f 30 -0.008 f 0.003
Error, %
1.2 0.9 1.3 1.4 1.7 1.6
Q
Table 111. Desorption Efficiencies of Various Solvents Solvent
Water Acetonitrile Methyl alcohol Methyl isobutyl ketone Butyl acetate Isoamyl acetate
Desorption,%
0 -25 -50 -40 -75 97-100
of the AA method over the electrode one as one of improved accuracy. Although still an indirect measurement of CS2, there is a direct measurement of the Cu which is complexed. The ease of using AA, once the proper operating parameters have been established, makes this an ideal method to adapt to routine pollution analysis. This method was, in fact, applied to samples which NIOSH provided. The first task was to find a solvent which would quantitatively desorb the CS2 from the charcoal and a t the same time be suitable for use in AA. The results of tests with various solvents are given in Table 111. Methyl isobutyl ketone, the usual organic solvent used in copper analysis, was not used since it was found to desorb only -40% of the sample. Isoamyl acetate fulfilled all the requirements, and it was used throughout. A straight-line calibration curve was prepared daily from charcoal samples by plotting absorbance vs. [CSz]. Results were checked against standards prepared with APDTC. No blank correction was necessary. The precision of replicate measurements was f l - 2 % . T h e biggest problems encountered with the charcoal-containing tubes were lack of reproducibility in injecting the samples and quantitative removal of the charcoal from the tubes. In a routine situation, however, replicate samples would be run. Significant amounts of CSZ were found in the backup sections (B) of the tubes in the NIOSH CSz-on charcoal samples. This resulted from their being stored for 3 weeks prior to analysis, for CS2 tends to equilibrate throughout the sampling tube on standing. Table IV compares the results of collaborative analyses performed by us and by P a t Quinn of NIOSH who used GLC analysis (flame photometric detector) after de-
944
ANALYTICAL CHEMISTRY, VOL. 47, NO. 6, M A Y 1975
csz injected
AA method
0.1 pl = 130 pg 0.3 380 0.5 630 0.7 880 1.0 1260
*
385 49 pg 565 rt 120 612 f 106 932 k 36
GC method
*
a3 13 pg 310 35 570 i 160 860 f 89 1290 f 63
sorption of CS2 with benzene or toluene. Discrepancies in the results were attributed to poor reproducibility in injecting the samples and probable losses due to shipment and storage. Interference studies were not done since all samples supplied were pure CSz. The main interference which would be encountered in routine analysis would be H2S. Inasmuch as CuS is insoluble in isoamyl acetate, H2S is not likely to interfere with this method. I t could, however, be eliminated by passing the air sample through a cotton plug which has been saturated with Pb(Ac)z or CdClp, a procedure which could be readily adapted here (13). The sensitivity of the method as outlined is 7 yg CS2/10 ml of solution. Using smaller volumes than 10.0 ml and an AAS with better electronics than the P E 303 would yield a sensitivity in the range of 1-5 yg. T h e main advantage of this AA method over the current spectrophotometric techniques is t h a t the use of a solvent extraction step affords the opportunity of concentrating samples of CS2 a t levels lower than the NIOSH detection limit of 6 yg/l. air for air samples greater than 1.2 liters. In addition, the sensitivities for Cu attainable with current AA units, on the order of 0.04 ppm, would allow air samples of 0.1 liter to be sampled, although it is unlikely that a samthis small would be taken.
LITERATURE CITED H.Brieger in "Toxicology of Carbon Disulfide," H. Breiger and J. Teisinger, Ed., Excerpta Medica Foundation, Amsterdam, 1967, pp 27-31, V. Vasak and J. Kopecky. /bid,, pp 35-41. P. M. Quinn. C. S. McCammon, Jr., and R. E. Kupel, Am. Ind. Hyg. Conference, . Boston, Mass., May 1973, No. 12. V. Vasak in "Toxicology of Carbon Disulfide," 1973, pp 18-20. F. J. Viles, J. lnd. Hyg. Toxicol., 22, 188 (1940). R. W. McKee, J. lnd. Hyg. Toxicol., 23, 151 (1941). F. A. Gunther and R. C. Blinn. "Analysis of Insecticides and Acaricides." Interscience, New York, NY, 1955, p 338. R. Truhaut, C. Bondine, Nguyen Phu-Lich, and A. Baquet, Arch. Mal. Prof., 33,341 (1972). T. E. Cullen. Anal. Chem., 36,221 (1964). "Threshold Limit Values, 1973," American Conference of Governmental Industrial Hygienists, P.O. Box 1937, Cincinnati, OH 45201, R. E. Kupel and L. D. White, Am. lnd. Hyg. Assoc. J., 32,456 (1971). R. R . Scharfe, V. S. Sastri, and C. L. Chakrabarti, Anal. Chem., 45, 413 (1973). M. B. Jacobs, "The Chemical Analysis of Air Pollutants," Interscience, New York, NY, 1960, pp 190-192.
RECEIVEDfor review July 24, 1974. Accepted January 20, 1975. The research reported here was conducted with the financial support of NIOSH in the form of Research Contract No. HSM-99-72-25.
