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Anal. Chem. 1981, 53, 929-931
H2 + 2H+ t,2e2AgC1
(anodic reaction)
+ 2e- + 2Ag + 2C1-
(cathodic reaction)
The chloridation seems to occur during the conditioning procedures. The readings obtained are linear with respect to the amount of hydrogein dissolved in solution. The response is essentially complete within 90 s. The lower detectable limit can be estimated as follows: Assuming Henry’s law holds, a solution saturated with. Hz contains 1.5 ppm of H2and gives a reading of 5.5 divisions on the panel. The lowest level of hydrogen attempted to be read was 20% Hz which gave a reading of 1.2.
1.5 ppm X 1.2 = 0.33 ppm of H2 5.5 LITERATURE CITED (1) Sweet, W. J.; Houchins, J. P.; Rosen, P. R.; Arp, D. J. Anal. Blochem. 1980, 107, 337-340. (2) Clark, L. C., Jr.; Bargeron, L. M., Jr. Sclence 1959, 130, 709-710. (3) Clark, L. C., Jr. U.S. Patent 3380905, April 30, 1968. (4) Olsen, R. R.; Srlnivasan, V. S. Anal. Chem. 1977, 49, 853-857.
RECEIVED for review November 24, 1980. Accepted March 3,1981. This research was supported by the Faculty Research Committee, Bowling Green State University, Bowling Green, OH 43403.
Automatic Liquid Injector for Headspace Gas Chromatography Rein Otson Bureau of Chemical Hazards, Environmental Health Directorate, Health and Welfare Canada, Tunney‘s Pasture, Ottawa, Ontario K1A OL2, Canada
General aspects and practical applicatilons of headspace gas analysis have been discussed in detail (1, 2). Static headspace chromatographic techniques have been successfully applied in areas such as the analysis of food and beverages (3) and the analysis of water ( 4 , 5 ) . When a large number of samples must be analyzed, the technique requires time-consuming manual injection of headspace aliquots into the gas chromatograph unless an autornated headspace sample injector, such as the system of the Moldel F45 (Perkin-Elmer Corp., Norwalk, CT) is available. Since such an injector was not available when a survey of volatile compounds present in a large number of consumer products was initiated, adaptation of available equipment, a Model 8020 liquid autosampler (Varian Associates, Inc., Palo Alto, CA), to perform automated headspace analyses was investigated.
EXPERIMENTAL SEC’TION Gas Chromatography. All analyses were performed on a Model 5840 gas chromatograph (Hewlett-Packard Co., Palo Alto, CA) equipped with an OIV-17,SCOT stainless steel column (50 ft X 0.020 in. i.d., Perkin Elmer Corp., Norwalk, CT) attached to a Hewlett-Packard capillary column inlet system operated in the splitless mode and maintained at 180 “C. For hydrocarbon analyses, the column was1 attached to a flame ionization detector (FID) and for trihalomethane (THM) analyses it was attached to a 63Ni,electron capture detector (ECD). Both detectors were held at 300 “C, and after each injection the column oven temperature was maintained at 60 “C for 3 min and then raised at a rate of 8 OC/min to 150 “C where it was held for 6 min. Nitrogen gas, passed through Oxiclear (Labclear, Oakland, CA) and molecular sieve traps, was uiaed for column carrier gas, at 4 mL/min flow rate, and detector makeup gas, at 25 mL/min flow rate. Autosampler. A Varian Model 8020 autosampler was interfaced with the gas chromeitograph and was operated in the manner prescribed in the autosampler instruction manual. Zero grade nitrogen gas was used to operate the autosampler pneumatic system. Autosampler vials (2-mL capacity) sealed with Tefloncoated silicone disks and screw caps were used for preparation of samples for headspace analysis. A rinse volume of about 200 p L was used for both sample and rinse vials. Reagents. The purity of all organic reagents was determined by gas chromatography. Composite stock solutions of four hydrocarbons (Chem Service, Inc., West Chester, PA) in nitrobenzene (Fisher Scientific Co., Pittsburgh, PA) were prepared to contain hexane, benzene, toluene, and o-xylene in the concentrations shown for sainples 1-5 in Table I. Three additional stock solutions, respectively containing lo9 of the hydrocarbon
concentrations for samples 1, 3, and 5, were also prepared for quantitation of hydrocarbons in headspace aliquots. Aliquots of methanolic (Caledon Laboratories Ltd., Georgetown, Ontario, Canada) solutions containing 0.20 mg of four trihalomethanes (Chem Service, Inc.) per milliliter of solution were injected into trihalomethane (THM) free water (2)to obtain aqueous, composite stock solutions. The aqueous solutions contained chloroform, bromodichloromethane,chlorodibromomethane,and bromoform at the concentrations corresponding to samples A-E in Table 11. Three composite solutions containing 5,10, and 50 ng/mL of each of the four trihalomethanes in hexane (CaledonLaboratories LM.) were also prepared for determination of THMs in headspace aliquots. A variety of consumer products, such as paints, paint removers, automotive and household cleaners, wood preservatives and sealants, and contact cements, were obtained. Procedure. Sample, blank, and rinse vials for headspace analyses were prepared by injecting 200-pL aliquots of composite hydrocarbon solutions, consumer products, or nitrobenzene and 250-pL aliquots of THM solutions, THM free water (containing 0.1% of methanol by volume), methanol, or hexane into sealed autosampler vials. The storage time between aliquot injection and headspace analysis and the ambient temperature at the autosampler were recorded. Sealed autosampler vials containing ambient laboratory air only were used for air blank analyses and air rinses. Headspace aliquots of 5 pL volume were used both for the autosampler injections and for the manual injections performed by means of a 1 0 - ~ L Hamilton syringe. Results from gas chromatographic analysis of aliquots of the solutions were used to construct calibration curves. These plots of peak area against the calculated amount of compound injected allowed estimation of the concentration of organics in headspace aliquots.
RESULTS AND DISCUSSION The Model 8020 autosampler principles of operation suggested that it could be used to sample and inject headspace above samples in the autosampler vials. It was shown that headspace rather then liquid was sampled and injected if less than 300 p L of consumer product was added to a vial. Volatile organic compounds in the consumer products were thus readily detected by the automated headspace chromatography technique. For some products, contamination of the autosampler transfer and injection system by compounds in the headspace caused a “memory effect”. The “memory” for volatile compounds was reduced when the contaminated system was rinsed with air from an empty, sealed vial. The analysis of some consumer products caused such high
0003-2700/81/0353-0929$01.25/0Published 1981 by the Amerlcan Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 53, NO. 6, MAY 1981 -__.
Table I. Typical Headspace Analyses Results for Composite Hydrocarbon Solutions hydrocarbon concentration (mg/mL), mean peak areaa (pV s), and RSD (%) hexane
benzene
-___
sample type
mg/mL
x
fiv s lo3
%
0.33 3.30 16.5 33.0 65.9 3.30 3.30
9.5 10.1 0.9 39.0 180 336 495 46.9 28.4
5.2 28 170 5.9 4.7 3.0 3.0 4.0 1.2
air blank nitrobenzene blank 1 2 3 4 5 2-IC 2-11d
PV s
mg/mL x l o 3 Autosampler 0.44 4.39 22.0 43.9 87.8 4.39 4.39
1.8 1.6 2.2 9.0 35.9 81.6 136 10.6 8.6
toluene %
22 29 14 5.0 6.4 4.2 3.8 4.0 1.8
PV s
o-xylene
mg/&
x lo3
%
32 33
0.43 4.33 21.7 43.3 86.6 4.33 4.33
0.5 0.7
