Anal. Chem.
1980, 52, 733-736
733
zymes. J. Biol. Chem. 1977. 252. 5939. (3) Markert, C. L. Science 1983, 740, 1330. (4) Chamoles, N.; Karcher, D. Clin. Chim. Acta 1970, 3 0 , 337. (5) Dawson, D. M.; Eppenberger. H. M.: Kaplan, N. 0. Biochem. Biophys. Res. Commun. 1985, 21, 346. (6) Hooton, 6.T. Biochemistry 1988, 7, 2063. (7) Kudirka. P. J.; Schroeder, R. R.; Hewitt, T. E.; Toren, E. C. Clin. Chem. 1978, 22, 471. (8) Chang, S . H.; Noel, R. R.; Regnler, F. E. Anal. Chem. 1978, 46, 1839. (9) Chang, S. H.; Regnler, F. E. US. Patent 4029563, 1977.
(IO) Schlabach, T. D.; Chang, S. H.; Gooding, K. M.; Regnler, F. E.
J.
Chromatogr. 1977, 134, 91. (11) Chang, S.H.; Gooding, K. M.; Regnler. F. E. J. Chromatogr. 1978, 125,
0. 00
' 16'
T I M E (PIIN)
Figure 9. Comparison of sequential, CK isoenzyme profiles from the same serum used in Figure 7. (A) Admission profile. The CK-MM and CKMB activities in (A) were 106.5 and 12.8 U/L, respectively. (B)Profile 18 h after admission. The CK-MM and CK-MB activities in (B) were 168.1 and 30.1 U/L, respectively
102. (12) Schroeder, R. R.; Kudirka, P. J.; Toren, E. C. J. Chmmtogr. 1977, 134. 83. (13) Schlabach, T. D.; Fulton, J. A,; Mockridge, P. B.; Toren, E. C. Clin. Chem. 1979, 25, 1600. (14) Fulton, J. A.; Schbbach, T. D.; Kerl, J. E.; Toren, E. C.; Miller, A. R. J . Chromatog. 1979, 775, 269. (15) Cohen, L.; Djordvitch. J.; Ormiste, Y. J . Lab. Clin. Med. 1964, 64, 355. (16) Roe, C. R.; Limblrd, L. E.; Wagner, G. S.; Nerenberg, S. T. J. Lab. Clln. Med. 1972. 80. 577. (17) Galen, R . S:;Relffel, J. A.; Gambino, S. R. J. Am. Med. Assoc. 1975, 232,145. (18) Williams, E. B.; Lyons, R. 6.Anal. Biochem. 1971, 42, 342. (19) Rosalki, S. B. J . Lab. Clin. Med. 1967, 69, 696. (20) Szasz, G.;Gruber, W.; Bernt, E. Clin. Chem. 1978, 22, 650. (21)FuRon. J. A.: Schlabach. T. D.: Kerl. J. E.: Toren. E. C. J. Chrometwr. I97gS 775, 283. (22)Schlabach, T. D.; Alpert, A. J.; Regnler, F. E. Clin. Chem. 1978, 24,
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1351
profiies were also detected and correctly predicted myocardial infarction.
ACKNOWLEDGMENT We thank William Dean, Corning Glass Works, Corning, N.Y. for supplying us with column support material and Paul Schneider, Biodynamics/bmc, Indianapolis, Ind., for providing some CK assay reagents. We are indebted to Timothy G. Kelly, American Instrument Co., Silver Spring, Md., for writing our file transfer program and assisting in program development and Ruth C. Ray1 and Dorothy N. Vacik for their help in preparing the manuscript. LITERATURE CITED (1) Hunter, R . L.; Markert, C. L. Science 1957, 725, 1294. (2) Report of the Subcommittee on Nomenclature of Interconvertible En-
(23) Tiicha, P. J. Clin. Chem. 1977, 23, 1780. (24)Tsung, S. H. Clin. Chem. 1978, 22, 173. (25)Wagner. G. S.;Roe, C. R.; Limbird, L. E.; Rosatl, R. A.; Wallace, A. G. Circulation 1973, X L V I I , 263. (26) Lederer, W. H.; Gerstbrein, H. L.; McCllntock, W. C. Am. J. Clh. Patho/. 1976, 66, 425. (27) Solni, E.; Hemmila, I. Clin. Chem. 1979, 25, 353. (28) Denton. M. S.:Bostick. W. D.: Dlnsmore. S.R.: Mrochek. J. Cffn. Chem. 1978, 24. 1408. (29) Schlabach, T. D.: Fukon. J. A.; Mockridge, P. B.; Toren, E. C., Clln. Chem., In press.
RECEIVED for review November 1, 1979. Accepted January 16,1980. This work was supported by Grant no. GM 24452 from the National Institutes of Health, and was presented in part at the 31st Annual Meeting of the American Association for Clinical Chemistry in New Orleans, La., July 1979.
Determination of Methanethiol at Parts-per-Million Air Concentrations by Gas Chromatography Rlchard Knarr and Stephen M. Rappaport" School
of Public Health,
Department
of Biomedical and
Environmental Health Sciences, University
A method is described for determining the air concentration of methanethlol. The sampling device, a 37-mm glass fiber filter Impregnated with mercurlc acetate, is suitable for either personal or area monltoring. Methanethiol is regenerated from the mercury mercaptide, formed on the fllter during sampling, by treatment wlth hydrochloric acid and Is dissolved in methylene chlorkle. Chantitation employs gas chromatography wlth flame photometric detection. The detection ilmit of 17 pg/m3 permits use of the method for determlning elther time-welghted average concentrations or 15min ceiling concentrations. The relative error of the method is I 1 0 % , while the relative standard deviation is I 1 %
.
Methanethiol is a commercially important gas which is used extensively in the manufacture of agricultural chemicals, pharmaceutical products, gas odorants, and specialty chemicals. It is also produced in large quantities as an unwanted
of California,
Berkeley, California 94720
by-product of paper manufacture and petroleum refining. The toxic effects of methanethiol have not been extensively investigated. I t is known that the LCW (lethal airborne concentration to l/z the animals) for mice was 1664 ppm (I) and that mice and rhesus monkeys exposed to 50 ppm for 90 d experienced mortality rates in excess of 40% (2). One human death has been attributed to exposure to airborne methanethiol ( 3 ) . Given the paucity of information concerning the health effects of methanethiol in man, standards and guides for occupational exposure have been based in part upon the offensive odor of this compound. Although the current OSHA standard for airborne methanethiol is 10 ppm, a Threshold Limit Value (TLV) of 0.5 ppm has been adopted by the American Conference of Governmental Industrial Hygienists (ACGIH) ( 4 ) and proposed by the National Institute for Occupational Safety and Health (NIOSH) (5). Significantly, this 0.5-ppm limit is suggested as an 8-h time-weighted average (TWA) TLV by ACGIH ( 4 ) and as a ceiling concentration
0003-2700/80/0352-0733$01.00/0 0 1980 American Chemical Society
734
ANALYTICAL CHEMISTRY, VOL. 52, NO. 4, APRIL 1980
which should not be exceeded for 15-min intervals by NIOSH (5). Since many people are occupationally exposed to methanethiol (more than 19 000 between 1972-74) ( 5 ) ,monitoring methods are needed to accurately determine air concentrations inhaled by workers. Ideally, these methods should permit personal sampling whereby a small collection device is attached to the worker's clothing (close to the breathing zone) and connected via plastic tubing to a battery-operated pump. The analytical procedure must be sensitive (at 0.5 ppm a 15-L air sample contains 15 kg of methanethiol) and specific for this compound. Procedures published thus far do not meet these criteria for air sampling and analysis. Methods employing simple absorption (6) and adsorption (7) were unsuitable for personal sampling since subambient temperatures were required to trap methanethiol from the air. Collection methods based upon conversion of methanethiol to the nonvolatile mercuric mercaptide (8-10) appeared promising but could not be applied t~ personal sampling without modification. Two of these procedures (8,9) employed aqueous solutions of mercury salts in glass bubblers, which are susceptible to breaking and spillage. The other procedure, developed by Okita (IO),used a filter which had been impregnated with mercuric cyanide as the collector. Although this method was developed for ambient air monitoring, the collection procedure was readily adaptable to personal sampling by substituting a smaller fiiter. However, the analysis (flame-ionization detector/gas chromatography) was insufficiently sensitive to measure methanethiol a t 0.5 ppm in the small air volumes obtained by personal sampling, and the regeneration of the thiol with strong acid required special apparatus. We report here a procedure for personal sampling and analysis which is both simple and specific for methanethiol. Air is drawn through a glass-fiber filter impregnated with mercuric acetate which converts the thiol to the mercaptide. Preliminary experiments indicated that the methanethiol collection and recovery efficiencies were equivalent with mercuric acetate and mercuric cyanide. We used mercuric acetate to avoid generation of HCN during the extraction procedure. Methanethiol is regenerated and extracted into an organic solvent in one step without special apparatus. Analysis employs gas chromatography with flame photometric detection to separate methanethiol from interfering substances and t o quantitate this compound in the nanogram range. Thus, the method is sufficiently sensitive to allow monitoring for either integrated (TWA) or ceiling exposures a t 0.5 ppm.
-
EXPERIMENTAL Production of Controlled Test Atmospheres. The dynamic system used to generate controlled test atmospheres of methanethiol in air (Figure 1)produced air concentrations from 0.1 to 1.0 ppm. Compressed air was dried with Ca2S04and filtered through a 0.2-pm pleated membrane filter (Gelman Instruments, Ann Arbor, Mich.). A small portion of the purified air stream continuously swept methanethiol from the generation chamber which contained a methanethiol permeation tube (30 cm in length, Metronics, Santa Clara, Calif.). Water, which was held at 39.9 A 0.01 "C in a constant-temperature bath, was circulated by a pump through the water-jacketed permeation chamber to maintain a constant temperature inside. The air stream emerging from the generation chamber was diluted with the bulk of the purified air in a Teflon chamber (3.2 cm i.d. X 76 cm). Three Teflon baffles in the midsection of the chamber ensured complete mixing, while a baffle at the exit prevented contamination with ambient air. Ten sampling ports were arranged radially around the chamber, 25 cm from the exit. Samples were withdrawn from these ports through in-line filter cassettes containg 37-mm impregnated filters. Flow rates were controlled with critical orifices a t the desired levels. When required, the dilution air was humidified by bubbling through distilled water. Wet and dry bulb
I
ck.Genemiion
I
Permeation
Vacuum Humidifier
Filter
Flgure 1. Test atmosphere generation system
thermometers were placed in the air stream immediately downstream from the humidifier to measure the relative humidity. A syringe pump (Harvard Apparatus, Millis, Mass.) metered a methylene chloride solution of potentially interfering compounds into the dilution air, where it vaporized and mixed with the test atmosphere. The effects of these compounds on the method were assessed by analyzing samples from this atmosphere. All components that contacted methanethiol were Teflon or glass, to minimize oxidation on active surfaces. The methanethiol generation rate was measured by weighing the permeation tube daily, at ambient conditions. The electrostatic charge on the tube was removed prior to weighing with a radioactive-charge neutralizer. The rate declined gradually over a 3-month period from 23.9 to 23.2 pg/min. Methanethiol concentrations were varied from 0.1 to 1.0 ppm by adjusting the dilution air flow rate from 116 to 11.6 L/min. Impregnation of Filters. Glass fiber filters (37 mm, type GF/D, Whatman Inc., Clifton, N. J.) were placed in a Petri dish and covered with a 5% (w/v) aqueous solution of mercuric acetate. Wet filters were removed from the dish, slipped into clips, and hung on a wire rack to dry. Analysis. The mercuric mercaptide formed on the filter during sampling was decomposed to yield methanethiol by shaking the filter in a 30-mL separatory funnel containing 10 mL of 25% by weight hydrochloric acid and 20 mL of methylene chloride. In order to prevent loss of the thiol, the exposed filter was folded and inserted into the neck of the separatory funnel, but not allowed to contact the liquid. The filter was then pushed into the funnel with the stopper, which was seated with the same motion. The funnel was shaken for 2 min without venting. After the phases separated, the methylene chloride was drained into a 5-mL serum vial which was sealed with a Teflon-lined rubber septum. A 2-pL aliquot of the methylene chloride extract was injected into a gas chromatograph (Model MT-222 Tracor, Inc., Austin, Tex.) equipped with a flame photometric detector (FPD) and a 2 m X 2 mm i.d. Teflon column packed with SO/lOO mesh Durapak OPN/Porasil C. Operating conditions were as follows: injector temperature, 250 "C; column temperature, 90 "C isothermal; detector temperature 190 "C; carrier gas: nitrogen, 50 mL/min; hydrogen, 150 mL/min; air, 60 mL/min; oxygen, 10 mL/min. Retention times were 45 s for methanethiol and 55 s for methylene chloride. Peak areas were measured by a digital integrator (Autolab Model 6300, Spectra-Physics, Inc., Santa Clara, Calif.) Calibration solutions were prepared by injecting 30 mL of methanethiol gas from a lecture bottle into 100 mL of methylene chloride in a 100-mL capped serum vial. The resulting solution was diluted to the desired concentration (&lo% of sample solutions) with methylene chloride. A fresh calibration solution was prepared daily. A chromatogram is shown in Figure 2. Calibration plota of (peak area)1/2vs. methanethiol concentration were linear over the working range, 0.5 to 3.0 ng/pL.
RESULTS A N D D I S C U S S I O N The accuracy and precision of the method were determined for both large (120 L) and small (13.5 L) sampling volumes at 23 "C and 0% relative humidity. Large-volume samples were collected in groups of 5 at air concentrations ranging from 0.1 to 1.0 ppm for 4 h a t 0.5 L/min. One group of 10 small-volume samples was collected at 0.5 ppm for 15 min at
ANALYTICAL CHEMISTRY, VOL. 52, NO. 4, APRIL 1980
735
Table 11. Recovery (%) of CH,SH from Samples Stored under Various Conditions ( 2 t s f o r 3 samplesIgroup) storage conditions time, desiccator, desiccator, days light, 23 " C dark, 23 " C dark, 2 3 " C dark, -17 " C 1
7 18
01 Time ( min ) Figure 2.
Chromatogram of 1.2-ng injection of methanethiol
Table I. Accuracy and Precision of the Method for Large and Small Sampling Volumes samno. of
pling dura-
L
ples
h
120 120 120 120 120 13.5
5 5 5 5 5 10
4 4 4 4 4 0.25
air volume. sam- tion.
CH,SH air
rel. concn, ppm error, known observed %
0.102 0.299 0.500
0.695 1.02 0.486
0.092 0.272 0.460 0.665
-9.4 -9.1
RSD, %
0.98 0.81
-8.0
1.3
-4.3
0.99 0.22 2.5
1.00
-1.6
0.435
-10.5
0.9 L/min. Data are summarized in Table I. The relative error for large-volume samples decreased from -9.4% a t 0.1 ppm to -1.6% a t 1.0 ppm while the relative error for the small-volume samples was -10.5% a t 0.5 ppm. These results suggest that the method should be accurate to within 10% of the true value for either integrated or short-term samples collected at concentrations in the range of 0.5 ppm, the proposed standard. The relative standard deviation (RSD) for large-volume samples decreased from 0.98% a t 0.1 ppm to 0.22% at 1.0 ppm and for small-volume samples was 2.5% a t 0.5 ppm. The 5 RSDs of the large-sample groups were pooled via a weighting procedure (11) to yield a single estimate of the RSD at 0.34%. If this method was applied to field sampling with pumps having RSDs of 5.0%, the expected precision would be -5.0% for integrated samples and -5-6% for short-term samples collected in the range of 0.5 ppm. Table I1 illustrates the stabilities of samples after collection. Thirty-six samples were collected from a 1-ppm test atmosphere a t 0.5 L/min for 1 h (30 L/sample) and stored under the indicated conditions. Obviously, significant losses of methanethiol resulted from storage under ordinary fluorescent lighting. However, no losses were observed among samples stored in the dark either at room temperature (23 "C) or a t
-
88.3 * 0.38 90.7 69.8 i 0.77 92.7 47.6 * 6.7 92.9
* t
i
1.21 92.2 0.75 92.7 1.07 90.9
f
t i
0.55 92.1 t 0.56 0.86 91.4 * 0.38 1.44 93.1 i 0.31
-17 O C for 18 d, These data imply that exposed samples should be protected from light prior to analysis. The method was also evaluated to determine the effects that humidity and potentially interfering substances may have. Groups of three samples were collected a t 23 "C for either 3 or 4 h from a test atmosphere containing 0.5 ppm of methanethiol. The test atmosphere system was adjusted to produce 4 sets of conditions: 0% RH, interferents absent; 0% RH, interferents present; 85 '% RH, interferents absent; and 85% RH, interferents present. All interfering compounds were present simultaneously a t 1.0 ppm. Three of the four compounds, hydrogen sulfide, dimethyl sulfide, and dimethyl disulfide, were chosen because their presence would be expected in many areas where methanethiol was measured. The fourth compound, propylene, was tested to determine the possible effect of alkenes which also react with mercury salts. Sampling flow rates of 0.5 L/min (120 L/sample) and 0.2 L/min (36 L/sample) were used for the collection of samples when interfering compounds were absent and present, respectively. No differences in recoveries of methanethiol (a = 94.2%) were observed for samples collected in the absence of interfering compounds at either humidity or for samples collected in the presence of interfering compounds a t low humidity. However, when samples were collected from a high humidity environment in the presence of interfering compounds, the recovery (109%) was higher. When the experiment was extended to test each interfering compound independently a t 1.0 ppm in a 85% RH environment, the recovery was 114% in the presence of dimethyl disulfide, but was essentially unchanged in the presence of the other three compounds (f = 92.4%). This experiment clearly demonstrated that the high recovery observed in the presence of high humidity and all four interferants was caused exclusively by dimethyldisulfide. Given the specificity of the analytical procedure, it was concluded that additional methanethiol was produced from dimethyl disulfide in the presence of water vapor and that the apparently high recovery was, in fact, indicative of the true methanethiol content of the filter. The method described offers significant advantages over the one developed by Okita (IO). The procedure of regenerating methanethiol from the mercaptide is considerably simpler, requires no special apparatus, and is more accurate and precise. The best results obtained with Okita's procedure in our laboratory showed a relative error of -12% and an RSD of 5.0%. With our recovery technique, the relative errors were -1% to -10% with RSD values from 0.2 to 1.3%. Substitution of the FPD for the flame ionization detector reduced the detection limit for methanethiol from 20 to 2 wg per sample. Thus, the collection device may be coupled with personalsampling pumps of low volumetric flow rate to evaluate either TWA or peak exposures (15 min) at 0.5 ppm. The collection procedure is not significantly affected either by humidity or by likely interfering compounds. Samples may be shipped and stored conveniently without loss prior to analysis.
ACKNOWLEDGMENT The authors gratefully acknowledge the advice of Steve Selvin concerning the statistical analysis of the data, and the
Anal. Chem. 1980, 52, 736-740
736
assistance of John Potter concerning the design and construction of the test atmosphere system. (6) (7) (8)
LITERATURE CITED ( I ) Horiguchi, M. J . Osaka City Med. Cent. 1960, 9 ,5257-93. (2) Sandage, C. "Tolerance Criteria for Continuous Inhalation Exposure to Toxic Material - 11. Effects on Animals of 90day Exposure to H,S, Methyl Mercaptan, Indole, and a Mixture of H,S, Methyl Mercaptan, Indole and Skatole", Report #ASD-TR-61-519 (11); Biomedical Laboratory, Aerospace Medical Laboratory, Aeronautical Systems Division, Air Force Systems Command, United States Air Force: Wright-Patterson Air Force Base, Ohio, 1961; 30 pp. (3) Shults, W. T.; Fountain, E. N., Lynch, E. C. J . Am. Med. Assoc. 1970, 211. 2153-54. (4) "Threshold Limit Values for Chemical Substances and Physical Agents in the Workroom Environment"; American Conference of Governmental Industrial Hygienists: Cincinnati, Ohio, 1978; p 21 (5) "Criteria for Recommended Standard....Occupational Exposure to nAlkane Mono Thiols, Cyclohexanethiol, and Benzenethiol"; U S . De-
(9) (10) (1 1)
partment of Health, Education, and Welfare, Public Health Service, Center for Disease Control, National Institute for OccuDational Safety and Health: Cincinnati, Ohio, 1978; p 3 Cave, G. C. 8. Tappi1963, 4 6 , 15-20. Charlton, J.; Sarteur. R.; Sharkey, J. M. OilGas J . 1975, 73, 96-100. Moore, H.; Helwig, H. S.; Graul, R. J. Am. Ind. Hyg. ASSOC.J . 1960, 21. 466-70. Fekistein, M.; Balestrieri, S.;Levaggi, D. A., J . Air. Poliut. ControlAssoc. 1965, 15, 215-17. Okita, T. Atmos. Environ. 1970, 4 , 93-102. Kendall, W. G.; Stuart, A. "the Advanced Theory of Statistics", Vol. 1; Charles Griffen and Co., Ltd: London, 1963; p 54.
RECEIVED for review October 29, 1979. Accepted January 17, 1980. This work was supported in part by the Grossman fund, by USPHS Grants 5 TO1 OH00020-12, and 08SlRR05441A18, and by the Northern California Occupational Health Center.
Capillary Gas Chromatography with Ultraviolet Spectrometric Detection M. Novotny" and F. J. Schwende Chemistry Department, Indiana University, Bloomington, Indiana 47405
M. J. Hartigan' and J. E. Purcell Analytical Department, The Perkin-Elmer Corporation, Norwalk, Connecticut 06068
A gas-phase UV absorption detector with a 50-pL cell volume and variable-wavelength capabllity is ideally suited for the selective detection of aromatic solutes emerging from widebore capillary columns. Capillary columns with smaller diameters can also be used but with certain sensitivity sacrifice. The descrlbed applications of capillary GC/UV-detection are UV-absorbing compounds in gasoline, volatiles of physiological fluids, and polycyclic aromatic mixtures. Utilization of this detector can be extended to chromophore-tagged molecules, as demonstrated with benzyl esters of fatty acids. The described UV detector has good sensitivity and response linearity.
Among the many selective detectors used today in chromatographic analysis, various optical spectroscopic detectors play a n important role. These include fixed-wavelength monitors as well as more recently introduced scanning devices a n d imaging detectors. T h e information sought with such instruments may range from simple quantitative analyses of selected components in complex sample matrices up to an acquisition of entire optical spectra during a chromatographic run. While optical detectors have been very common in liquid chromatography, only a few studies have dealt with gas-phase optical spectroscopic detectors to date. With the technological advances of Fourier-transform IR spectroscopy during the past several years ( I ) ,new identification possibilities are becoming attractive in the fields of both gas and high-performance liquid chromatography. In addition, Hausdorff (2)has demonstrated that a simple selective IR monitor can be a useful device in GC peak identifications. When a nondispersive IR instrument is manually tuned to measure absorbance in a given spectral 'Present address: D e l t a Associates, Inc., M i l p i t a s , Calif. 95035. 0003-2700/80/0352-0736$01 .OO/O
region, various sample components can be selectively traced in complex mixtures. Although structural information potentially obtained with UV absorption instruments is considerably less distinct, somewhat similar considerations are applicable. Uses of heated gas-phase detection cells for both fluorescence (3-7) and UV measurements (8, 9) have been investigated. Kaye evaluated the basic instrumental variables involved in UV detection for packed columns, including the possibilities of repetitively scanning a narrow spectral range in 20-s intervals (8). While the detector sensitivity was better than for a typical thermal conductivity cell, the figures are about 2-3 orders of magnitude different from the measurements obtained in this report. Merritt et al. (9) developed their UV gas-phase monitor as an integral part of a process stream analyzer. The selectivity of their detector was found advantageous for a petrochemical problem, as aromatics could be selectively traced in the presence of other hydrocarbons. In this study, a standard variable-wavelength UV-visible detector for HPLC was modified to permit an effective coupling of such a detector to GC capillary columns. A 50-pL detector cell permitted an easy coupling with high-efficiency glass capillary columns, while its sensitivity was about three orders of magnitude greater than the previously described devices of this type (8, 9). The limit of detection for naphthalene was determined and compared to typical flame-ionization detection data under similar chromatographic conditions. Several applications of capillary GC with this detector are demonstrated. These applications attest to unique capabilities of the detector in typical high-resolution GC analyses. These include detection and/or quantitation of aromatic compounds in complex sample matrices such as gasoline or the concentrate of volatiles in human urine. While wide-bore (0.7-mm i.d.) capillary columns are ideal to use with this detector, the problems of excessive cell volume @ 1980 American Chemical Society
