753
Anal. Chem. 1986, 58,753-755
Determination of Chloroacetyl Chloride in Air by High-Performance Liquid Chromatography Andrew J. Klein,* Susan G . Morrell, Orville H. Hicks, a n d J i m m y W. Worley
Technology Division, Monsanto Agricultural Company, 700 Chesterfield Village Parkway, St. Louis, Missouri 63198
An HPLC procedure has been developed for the determlnatlon of chloroacetyl chloride (CAC) In alr. CAC Is collected on Tenax-GC coated wlth 9-[(Nmethylamlno)methyl]anthracene (MAMA) packed in glass tubes. The MAMA acts as an In SHU derlvatlrlng agent for CAC, and the resulting amide Is solvent desorbed from the Tenax support and analyzed by HPLC with fluorescence detectlon. Standard vapor concentrations of CAC were generated in sllanlzed glass for laboratory valldatlon In the range of 5-2500 ppb CAC based on a 5-L air sample. The average recovery was 79% wHh a pooled relatlve standard devlatlon of 0.083. Up to 100 L of alr was sampled and slmllar recoverles were obtalned lmplylng a practical llmlt of quantlflcatlon 1 ppb. The llmlt of detectlon for the MAMA derlvatlve of CAC, N-(9-anthracenylmethyl)2chlor~Nmethylacetamlde,under optbnal condltlons Is less than 1 pg.
Chloroacetyl chloride (CAC) is a reactive material used in industry as a chemical intermediate. Sensitive methods for its determination in workplace in air are important because of its reactive nature and irritating effects on the respiratory system (1). The American Conference of Governmental Industrial Hygienists has recently adopted a threshold limit value (TLV) for 8-h time weighted average exposure to CAC of 0.05 ppm (2). CAC can also be produced by photooxidation of chlorinated hydrocarbons and may be an important sink for these compounds in the atmosphere ( 3 , 4 ) . Several methods for the determination of CAC in air have been published. These include a liquid impinger method, which collects acid chlorides in 2-propanol, followed by GC analysis of the resultant ester using electron capture detection (ECD) (5). The limit of detection for CAC using this method is about 1 ppm and is therefore unsuitable for TLV determinations. Another impinger method, which is considerably more sensitive, relies on the formation of a trichlorophenate ester of CAC followed by GC-ECD (6). This method has been successfully applied to TLV determinations of CAC in workplace air but suffers from the usual disadvantages of glass impingers containing toxic chemicals in solution. A third method samples CAC with commercially available silica gel tubes (7). CAC is immediately hydrolyzed on the silica gel and the resultant chloroacetate and chloride determined by ion chromatography. This method is not specific for CAC, since other sources of chloroacetate such as chloroacetic acid or anhydride could interfere. In addition, the sensitivity of this method is just barely adequate for TLV determinations of CAC. This paper describes a sensitive, selective method for the determination of CAC in workplace air that replaces fragile glass impingers with a solid sorbent for collection and provides an alternative to ion chromatography for the quantification of CAC. The latter feature will be especially useful in small industrial hygiene laboratories, which may not be able to dedicate an instrument to one method that may be used infrequently. 0003-2700/66/0356-0753$01.50/0
Scheme I 0
/
I
‘?CH2C1
I1
Swedish workers have described sensitive procedures for the determination of isocyanates in air, based on derivatization with 9-[(N-methylamino)methyl]anthracene(MAMA) to form the corresponding ureas, which can be determined by HPLC with UV or fluorescence detection (8-10). CAC should readily react with MAMA to form the stable amide N-(9anthracenylmethyl)-2-chloro-N-methylacetide, which could then be detected by HPLC with fluorescence or UV detection (Scheme I).
EXPERIMENTAL SECTION Instrumentation. A Du Pont Model 880 pump was used for all chromatographic determinations. The detectors used were a Du Pont variable wavelength UV spectrophotometer, a Perkin-Elmer Model LS-4 dual grating fluorescence spectrometer, or a Varian Fluorochrom filter fluorescence detector. A Waters Associates Model 710B autosampler was used for injection. A data system designed in-house and based on a Digital Equipment PDP 11/70 was used for all data reduction and analysis. The chromatographic column was thermostated at 40 “Cwith a Du Pont column oven. A 25 cm X 4.6 mm Du Pont Zorbax CN column (5 gm packing) with a Brownlee CN-GU 3 cm X 4.6 mm guard column, also with 5-pm packing, was used throughout. The guard column was replaced when the back pressure increased to unacceptable levels and could not be decreased by flushing with tetrahydrofuran. The mobile phase was nominally 70/30 hexane/ethyl acetate (v/v) with approximately 0.2 % triethylamine added. Purified He was used as a sparge gas (1-2 mL/min) to prevent bubble formation and ensure trouble-free pump operation. A flow rate of 2.0 mL/min was employed. With this configuration, operating pressures were 35-70 bar (500-1000 psi). The excitation monochromator on the grating detector was adjusted to 313 nm and the exit slit set to give a 15-nm full width at half maximum (fwhm) band-pass. Emission was monitored at 440 nm through a 20-nm band-pass slit. A 7-60 excitation filter (300-400 nm band-pass) and 3-74,4-76emission filter combination (385-480 nm band-pass) were used with the Varian filter fluorometer. Du Pont Model P4000 personnel sampling pumps were used for air monitoring. The packed collection tubes (see below) were attached to the personnel pump with a short piece of Tygon tubing. A General Eastern Model 400C % relative humidity/temperature detector was used to measure relative humidity. CAC Standard Generator. Dynamic CAC vapor standards were generated in a modified 3/16 in borosilicate glass tee. About one-fourth of the long arm of the tee was removed, and a poly(tetrafluoroethylene) (PTFE) union was attached to each end of 0 1986 American Chemical Society
754
ANALYTICAL CHEMISTRY, VOL. 58, NO. 4, APRIL 1986
the tee. A PTFE backed silicone rubber septum was placed in the union on the shortest arm of the tee. A drying tube filled with calcium chloride was attached to one wm with a PTFE union to remove moisture from air passing through the tee, and the remaining arm of the tee was attached to a sampling tube (see below). The assembled tee was deactivated with a 10-pL injection of 30% dichlorodimethylsilane (DCMS) immediately prior to each use. CAC vapors were generated by injecting 10-pL aliquots of standard CAC solutions in dry toluene into the tee with air flowing through the standard generator. Reagents. All solvents were Burdick and Jackson, Distilled in Glass. Reagent grade CAC was obtained from Fisher Scientific and was used as received. The 9-[(N-methylamino)methyl]anthracene was obtained as the hydrochloride from Carston Sango, Fagelhundsvagen 52, S-222 53 Lund, Sweden, and was purified N-(9by recrystallization from ethanol before use. Anthracenylmethyl)-2-chloro-N-methylacetamide(11)was prepared by the following procedure. To 500 mL of water was added 2.87 g (0.011 mol) of MAMA-HCl. The solution was made basic by dropwise addition of 1 M sodium hydroxide. The free amine was extracted with two 200-mL portions of toluene and the toluene layer dried over sodium sulfate in an amber bottle. CAC (1.5 mL, 0.020 mol) was dissolved in toluene, which had been stored over calcium hydride to remove water. Triethylamine (3.0 mL) was added, and the mixed solution added to the MAMA solution. The reaction mixture was stirred for 2 h at room temperature in an amber container to preclude photodecomposition. After the reaction was complete, the toluene was extracted two times with approximately 100 mL of a saturated solution of sodium bicarbonate, followed by two 100-mL extractions with 1%HCl. The toluene layer was then dried over sodium sulfate, followed by rotary evaporation. The crude product was recrystallized from toluene to give 1.7 g (0.006 mol) of purified material (46% yield). Anal. Calcd: C, 72.60; H, 5.42; N, 4.70. Found C, 72.68; H, 5.46; N, 4.70. 'H NMR in CDCl,; d 8.5-7.3, m, 9 H; d 5.6, s, 2 H; d 4.2, s, 2 H; d 2.6, s, 3 H. Mass spectrum: m/z 297, M'.; m/z 262, loss of C1; m / z 248, loss of CH2C1; m/z 191; m / z 77; m / z 42. Preparation of MAMA Coated Tenax. For approximately 10 sampling tubes, 20 mg of recrystallized MAMA-HC1was dissolved in 15 mL of 0.1 M HC1. The aqueous solution was extracted with two 15-mL portions of toluene. The toluene was discarded and the aqueous phase made basic by addition of 15 mL of 1M sodium hydroxide, which caused the formation of a milky white precipitate. The free MAMA was then extracted with two 15-mL portions of toluene. The toluene layer was dried over calcium hydride in an amber vessel. Meanwhile, 2 g of Tenax-GC (60-80 mesh) was purified by extracting with boiling toluene. The toluene was removed, and the Tenax-GC stored in a round-bottom flask covered with aluminum foil to protect it from light. After filtration to remove the drying agent, the toluene solution containing the free MAMA was transferred into the flask containing the Tenax-GC. The vessel was stoppered and intermittently swirled over a 45-min period. The toluene was then removed with a gentle stream of purified nitrogen over a 2-4-h period. The coated Tenax was then transferred to an amber bottle and gently mixed with a spatula to form a free-flowing material, which can be readily packed into sampling tubes. Preparation of Sampling Tubes. Sampling tubes were prepared in-house and were fabricated from 0.4 mm i.d. borosilicate glass with an 11.5-cm lead section and a 4-cm backup section. The empty tubes were deactivated with a 30% DCMS in toluene solution immediately before packing. To pack the sampling tubes, a DCMS treated glass wool plug was positioned between the lead and backup sections of an empty tube. Approximately 160 mg of MAMA coated Tenax-GC was placed into the lead portion of the tube and secured with another deactivated glass wool plug. Approximately 40 mg of packing was then placed in the backup section of the tube and secured with another glass wool plug. The tubes were then sealed with PTFE tape and polyethylene caps and stored in the dark for no more than 1week prior to use. Air Sampling. Laboratory air was sampled with Du Pont Model P4000 pumps after connecting a sampling tube to one arm of the standard generator with a PTFE union. A typical field or laboratory sample was collected by drawing air through the
416
393
I 300 h "rn
300
k
400 h nm
Figure 1. Fluorescence spectra of N-(9-anthracenylmethyI)-2chioro-N-methylacetamide: (A) excitation spectrum, emission 4 16 nm; (B) emission smctrum. excitation 254 nm.
sampling tube at 0.1 L/min for 50 min. Field fortifications were made by direct addition of a CAC solution to a prepared tube. HPLC Analysis, After sample collection, the front and backup section of the sampling tube were transferred to a 4-dram vial and extracted at room temperature with 5.0 mL of toluene. The extraction took place over 30 min with gentle agitation,after which the toluene was decanted and filtered through a 0.45-pm membrane filter directly into an autosampler vial. External standard calibration curves were constructed from authentic 11.
RESULTS AND DISCUSSION A pilot study to determine the feasibility of using MAMA as a derivatizing agent for CAC was performed with glass impingers. A CAC solution was injected directly into a toluene solution containing a thousand-fold molar excess of MAMA, and the reaction was shown to be complete and quantitative a t the shortest time tested, 30 s. To determine the loading factor for the Tenax, a similar thousand-fold excess of MAMA was provided in the front section of the sampling tube for the amount of CAC in 10 L of a 20 ppb air sample. Figure 1 presents the excitation and emission spectra of a dilute solution of the amide, I1 in acetonitrile. Nearly identical fluorescence spectra were obtained with the amine, I demonstrating that chloroacetyl substitution has only a minor effect on the fluorescence spectrum of the anthracenylmethyl moiety. Thus any quantitative method must separate unreacted I from 11. A normal-phase HPLC separation based on a CN bonded phase provided quite satisfactory for this separation, allowing the derivative I1 to elute before the large peak for unreacted amine. An excitation wavelength of 255 nm and an emission wavelength of 416 nm should be chosen for maximum sensitivity of detection for 11. Under these conditions, 1 pg of I1 (injected) can be detected. Such extreme sensitivity was not required for TLV determinations of CAC in air, so excitation and emission wavelengths of 313 and 440 nm were chosen for method validation with the grating spectrometer. These wavelengths corresponded to commonly available transmission filters for the filter based detector, which was proposed for use at manufacturing facilities. The method was validated a t eight different levels corresponding to 5-L air samples containing from 5 to 2500 ppb CAC. Appropriate amounts of CAC in toluene were injected into the standards generator, and 5 L of air (25-5070 relative humidity) was drawn through the standard generator and sampling tube with a personnel pump calibrated for a sampling rate of 0.1 L/min. An impinger method was used to verify proper operation of the standard generator (6). Sideby-side comparison of the two methods gave identical results. After sampling, the front and backup tube were separately extracted, the extracts filtered, and aliquots injected. Derivative I1 eluted in approximately 4 min, and another in-
ANALYTICAL CHEMISTRY, VOL. 58, NO. 4, APRIL 1986
Table 1. Laboratory Validation at Ambient Relative Humidity
Table 11. Effect of Sampling Rate and Volume on CAC Recovery volume,
rate,
CAC in air,
recovery,
PPb
N
%
RSD
L
mL/min
PPb
%
4.92 6.40 24.6 53.3 107 246 666 2460
7 4 7 4 4 6 4 8
70 56 76 84 87 81 88 79
0.11 0.12 0.11 0.022 0.051 0.066 0.060 0.061
10.0 10.0 13.5 15.0 20.0 20.0 20.0 20.0 20.0 23.0 30.0 86.0 86 86 107
450 450 45
1250 1250 9.0 8.0 625 625 625 625 625 625 1.0 12.5 12.5 12.5 12.5
CAC in air,
recovery,
jection could be made after elution of I. Under the isocratic conditions used in this study, approximately 25 min was required for complete elution of I. Sample throughput could be increased via gradient elution if required. Quantification of I1 was by peak height, using an external standard calibration curve. Calibration curves were linear over more than 3 orders of magnitude, from 1.0 to 4000 ng/mL. Table I presents the results of a laboratory validation of the method. The average recovery was 79% with a pooled relative standard deviation of 0.083. Bartlett's test (11)yields a x2 value of 9.157, compared to a critical value of 18.49 at the 1% significance level for 7 degrees of freedom (number of test levels less one), indicating the relative standard deviation cannot be considered inhomogeneous or nonuniform throughout the validation range. Breakthrough to the backup tube was not observed during any of the 44 laboratory validation tests. The method was tested at two concentrations (5 and 250 ppb) under conditions of low and high relative humidity (6 and 96%). Mean recovery (* standard deviation, n = 6) for the lower CAC concentration was 74 f 7% at 6% relative humidity and 87 f 10% at 96% relative humidity. Likewise the higher concentration gave 88 f 6% and 76 f 11% at low and high humidity, respectively. A two tailed t test indicates a slight but significant difference in recovery of CAC for both concentrations at both relative humidities at the 0.05 significance level. Cochran's test (12)for homogeneity of variance indicates that, at the 5% significance level, the variance of the method at 96% relative humidity cannot be considered different from the variance at 6% relative humidity. The flexibility of the method was demonstrated by sampling different volumes of air at different sampling rates. These results are presented in Table 11. The recovery of CAC was high in all cases, thus the method can be used for short-term personnel monitoring or for relatively long-term TWA type determinations. The longest collection time was 17.8 h for a 107-L air sample. Samping tubes should be freshly prepared and promptly analyzed for reliable detection of low levels of CAC. The tubes can be stored for up to 1week if protected from light. Storage for longer periods of time results in chromatographic interferences. Recovery of CAC was unaffected after storage for up to 3 days of samples collected on MAMA coated Tenax.
755
60
460 460 100 100 100
100 100 100
100 100 100
79 100
78 74 87 90 93 90 83 83 93 94 96 96 83
The extract solution was stable for at least 2 weeks when stored in the dark at 4 "C. The method was field tested at a site of CAC manufacture on four separate occasions over a 5-week period. Over 110 area and personal samples were taken, and breakthrough was observed in two tubes from areas of high (>400 ppb) concentration. The amount of CAC in the backup tube was only 1 to 3% of that in the front section, however. Twenty-nine field fortifications over the range of 5-270 PPB CAC were prepared and workplace air was drawn through the spiked tubes. An average recovery of 69% with a standard deviation of 14% was obtained. Similar results (75 f 13%, n = 14) were obtained with direct spikes on the tube (field fortified tubes with no air drawn), indicating workplace air had little or no effect on recovery of CAC. Registry No. I, 73356-19-1; 11, 100206-57-3;CAC, 79-04-9.
LITERATURE CITED Patty, F. A.; Fassett, D. W.; Irlsh, D. D. "Industrial Hygiene and Toxicology", 2nd ed.; Interscience: New York, 1963; Vol. 11, pp 1826- 1827. Threshold Limit Values for Chemical Substances and Physical Agents in the Work Envlronment for 1983-1984, American Conference of Governmental Industrial Hyglenists, 1983. Gay, B. W., Jr.; Hanst, P. L.; Bufallni, J. J.; Noonan, R. C. Environ. Sci. Techno/. 1976, IO,58. Butler, R.; Snelson, A. J. Air Polht Control Assoc. 1979, 29, 833. Dahlberg, J. A.; Klhlman, I . B. Acta Chem. Scand. 1970, 2 4 , 644. Langvardt, P. W.; Nestrick, T. J.; Hermann, E. A,; Braun, W. H. J. Chromatogr 1978, 153 443. McCullough, P. R.; Worley, J. W. Anal. Chem. 1979, 51, 1120. Sango, C.; Zimerson. E. J. Liq. Chromatogr. W80, 3 , 971. Andersson, K.; Gudehn, A.; Levin, J.-0.; Nilsson, C.-A. Chemosphere 1082, 1 1 , 3 . Gudehn, A. J. Chromatogr. 1984, 301,481. Bethea, R.; Duran, B.; Bouillion, T. "Statistical Methods for Engineers and Scientists"; Marcel Dekker: New York, 1975; pp 247-251. Caulcutt, R.; Boddy, R. "Statistics for Analytical Chemists"; Chapman and Hall: London, 1983; pp 70-71.
.
RECEIVED for review August 12, 1985. Accepted December 2, 1985.
