United States Environmental Protection Agency Environmental Sciences Research Laboratory Research Triangle Park NC 27711 Research and Development EPA-600/S3-83-058 Sept. 1983 Project Summary Optimization of GC/MS Based Tenax Collection Method for Toxic Organics Barbu Demian and Edo D. Pellizzari The sampling of vapor-phase organ- ics in the presence of reactive inor- ganics using the Tenax GC sampling cartridge was investigated. To differen- tiate between pollutants in air and those formed from in situ artifact reac- tions, deuterated organics were em- ployed in both laboratory and field experiments, and any subsequent arti- fact products were detected by capil- lary gas chromatography/mass spec- trometiy/computer [(GC)VMS/COMP] techniques. Artifacts produced by Tenax GC itself and by reactions between adsorbed species were investigated using statistical methods. This Project Summary was developed by EPA's Environmental Sciences Re- search Laboratory, Research Triangle Park. NC. to announce key findings of the research project that is fully docu- mented in a separate report of the same title (see Project Report ordering information at back). Introduction The characterization and measurement of minute amounts of hazardous com- pounds in ambient air has, for many years, been seriously hampered by the lack of reliable sampling systems. Techniques have been developed to concentrate or- ganic vapors from large volumes of atmos- phere and to transfer the collected vapors to an analytical system. There is, however, a paucity of experi- mental data concerning artifact studies on collection devices for vapor-phase organ- ics. Investigators have had a propensity for accepting the viability of the collection step prematurely while emphasizing de- velopment of other steps in analytical procedures. In fact the literature is replete with analytical methods for analysis of a few vapor-phase components in complex mix- tures using various instrumental methods. Nonetheless, it should be noted that none of these procedures can be considered superior since the collection method is a common denominator among all the ana- lytical methods, and appears to be the weak link With the elucidation of nitrosamine presence in ambient air, serious consid- eration was given to potential artifact for- mation during collection. In fact, a plethora of collection methods for nitrosamines occurred. Artifacts associated with cryo- genic traps were readily apparent,and modifications ensued which eventually lead to using a sorbent cartridge impreg- nated with sulfamic acid to inhibit the in situ nitrosation of secondary amines. An approach to detecting, identifying, and quantifying halogenated hydrocar- bons in ambient air has involved using a Tenax GC cartridge combined with high resolution gas chromatography/mass spec- trometry/computer [(GC)2/MS/COMP] analysis. The primary concern was to use a Tenax GC sorbent that has been previously employed for collecting vapor-phase or- ganics in ambient air. Since the Tenax GC cartridge may concentrate reactive com- pounds from an atmosphere containing, for example, ozone (03), nitrogen oxides (NOX), molecular halogen such as chlorine (CI2) and bromine (Br2), in situ formation of artifact products may occur, even though inorganic gases do not appreciably ac- cumulate on the sorbent. Preliminary studies indicated that a more in-depth study was needed. The objectives of this research program were: (a) to examine the potentiaIly trou ble- ------- some chemical group types that exhibit reactivity with the commonly occurring inorganic gases in ambient air; (b) to conduct a series of controlled laboratory experiments to determine the extent, if any, of artifact problems associated with the direct interaction of these inorganic gases with Tenax GC itself; (c) to evaluate the artifact problems, if any, associated with organics on Tenax GC in the presence of atmospheric concentrations of inorganic gases; (d) to develop a way to minimize potential artifacts if they exist; and (e) to evaluate and apply potential corrective measures that minimize artifact production under field sampling conditions. Effects of Ozone and Nitrogen Oxides A 23 factorial experiment was planned to assess the ozone/nitric oxides/humid- ified air (03/NOX/H20) combination ef- fect on Tenax. For quantitative analysis, the gas chromatographic system was cali- brated with external standards. The identity of the major Tenax GC decomposition products was established by GC/MS methods. Clean, "virgin" Tenax GC cartridges were exposed to air containing 03/NOX/ H20, and pertinent information regarding Tenax GC cartridge exposure was obtained. The most important Tenax GC decom- position products were benzaldehyde, acetophenone, and phenol, indicating ozonolysis to be the polymer's major chemical reaction. After breakdown of the polymer backbone, further reactions of the primary degradation products lead to the relatively stable compounds actually de- tected. This result corroborates the many reports citing that interaction with atmos- pheric O3 is the main degradative mech- anism of polymeric materials. Humidity had a strong effect This is important since more attention should be given to artifact formation from Tenax GC when sampling air with a high relative humidity. The ozone concentration and N02 con- centration behaved additively. The three major decomposition products were found in easily detectable and.dosable quantities, even in "clean" cartridges. It appears, however, that analysis for any of the three major decomposition products at levels below 100 ng/L with Tenax GC sampling is not possible without taking special precautions. Effects of Sulfur Oxides Tenax GC cartridges were exposed to 30 L of air containing 03, sulfur oxides (SOX), and NOX at different humidity levels. The major Tenax GC decomposition prod- ucts were confirmed but no compounds that could identify the presence of SOX could be detected. Effects of Chlorine Tenax GC cartridges were exposed to 03, CI2, and humidified air. The same major decomposition products were ob- served. Effects of Tenax GC Aging Substantially lower levels of decompo- sition products were found in sampled air containing SOX and CI2. This effect was not related to the nature of the reactive inorganic gas (in all experiments 03 was present, the main factor in polymer degra- dation), but to the history of the Tenax GC cartridge. Recycled Tenax GC cartridges were used in the SOX and CI2 series. The hypothesis that cartridge history was the main factor in the total quantity of degradation prod- ucts was tested using the same cartridge exposed to 30 L of air in 30 min, with 100 ppb 03, 1 50 ppb NOX, and 60% humidi- fied air. The quantities of degradation products decreased by an order of magni- tude after five analysis cycles. Artifact Products from Adsorbed Compound Reactions Tenax GC cartridges (sorbent bed di- mensions, 60 mm length x 13 diameter) were loaded with d10-cyclohexene or d5- ethanol. For quantitation, 2-fluorobiphenyl was used as an internal standard. Stand- ard solutions of d^-cyclohexene and 2- fluorobiphenyl were prepared by weighing and dissolving in pure methanol. The loaded cartridges were exposed to an air flow containing inorganic gases in the concentrations listed below (inorganic gases are potential generators of artifacts by reaction with the adsorbed d^-cyclo- hexene: CI2 maximum concentration, 564 ppb 03 maximum concentration, 1,000 ppb N0/N02 maximum concentration, 500 ppb S02/S03 maximum concentration, 400 ppb humidified 50% at 25°C air For the low concentration range of reac- tive inorganic components in the sampled air, no deuterated cyclohexene product was detected. At higher chlorine concen- trations, d10-dichlorocyclohexane was found. A nondeuterated dichlorocyclc- hexane was also identified in the same samples, probably from CI2 reacting with cyclohexene (a contaminant). Deuterated compounds derived from d5-ethanol and contaminants typical for Tenax GC were identified as early eluting compounds (i.e., contaminants). The potential oxidation products - acetaldehyde and acetic acid - were not detected during GC/MS analysis. Artifact Inhibition with Impregnated Filters A series of filters was impregnated with various reducing agents for03. The sodium thiosulfate impregnated glass fiber filters appear to be the best in quenching ozone. Relatively good - but less spectacular - results were obtained for N02 quenching. The inclusion of sodium lauryl sulfate in the impregnating solution was proposed with the view that a surfactant would lower the solution's surface tension and allow a better wetting of the filter, thus improving overall performance. This be- havior was observed for the hydrophobic Teflon filters, which cannot be impreg- nated uniformly with reducing agents in the absence of surfactants. Studies on Artifact Problems Under Field Sampling Conditions The results from laboratory experiments suggested two types of filters for best overall performance: glass fiber filters im- pregnated with sodium thiosulfate and Teflon filters impregnated with sodium thiosulfate/sodium lauryl sulfate. The major objective in designing the field ex- periments was to test these two types of filters for inhibition of Tenax GC decom- position and for reduction of in situ reac- tions of adsorbed compounds. The deuterated compounds selected and the possible artifactual reactions were as follows: (1) d10-cyclohexene: chlorination and oxidation; (2) d6-benzene: aromatic substitution and oxidation; and (3) d8-dioxane: oxidation (peroxide for- mation). In conducting field experiments, two sorbent cartridges were run parallel. One cartridge was protected by an impreg- nated filter and the other cartridge by an unimpregnated filter. The objectives using (GC)2/MS/COMP analysis were as follows: (1) assess the recovery of deuterated compounds from exposed cartridges; ------- (2) identify reaction products of deu- terated compounds; and (3) quantify adsorbed volatile organic compounds, i.e., determine the trends in the quantities found, relative to using impregnated filters. The statistical analysts of aromatic com- pound data was restricted to the higher concentration range, i.e., more than 300 ng benzene/cartridge, in order to avoid unaccountable contamination effects. Only for toluene was a positive difference statis- tically significant. The loss of the aromatic compounds by further reaction of adsorbed species was, therefore, negligible at the level of sensitivity of the analytical method. The following were excluded from the statistical analysis of the halogenated compound data: (1)1,2-dichloroethane, due to the high concentration level in air; (2) 1,2-dibromoethane, since it is prac- tically absent; and (3) carbon tetrachloride and dichloro- benzene, which are present at very low concentrations. The statistical analysis was restricted to the higher concentration range for the halogenated compounds as well (same Tenax cartridge as for aromatics). The collection of chloroform and tn- chloroethane data was erratic and, there- fore, useless in these experiments. For trichloroethylene, a positive difference was statistically significant fourtimes, and for tetrachloroethylene, only once. Again, there was some evidence that the impreg- nated filter was preventing sample loss by further reaction of the adsorbed compound if it was relatively reactive. It was highly significant that the evi- dence for sample loss by artifact reaction was positive only for unsaturated com- pounds (cyclohexene, trichloroethylene, tetrachloroethylene), which were more re- active toward 03. The phenol data were also unreliable. Due to their strong acidic nature, phenol and acetic acid are subject to serious limitations in trace analysis by chromato- graphic methods, the best deactivated capillaries bind significant quantities ir- reversibly. Conclusions and Recommendations (2) The tr-h'-i f.v^oit, uetcrmining the qnantities of artifacts generated were, in order of decreasing importance, as follows: (a) 03 concentration of sampled air; (b) Tenax cartridge age; (••) humidity of sampled air; (d) "Concentration of NOX; and (e) concentrations of other reactive comp unds (SOX, CI2). (3) Artifact i -••ot'ons of adsorbed species were fount, to be: (a) relativeK unimportant for aromatic-; and saturated halogenated com- pounds; and (b) significant for more reactive com- pounds, e.c,., unsaturated com- pounds such as i'ichloroethylene and tetrachloroethyltirit. (4) Sodium thiosulfate impregnated fil- ters were found to be: (a) effective in artifacts generated by Tenax GC itself; and (b) effective in reducing artifact reac- tions of reactive adsorbed species. Use of sodium thiosulfate impregnated glass fiber filters for sampling with Tenax GC cartridges is strongly recommended. Based on the results of laboratory and field experiments on artifact formation, three important recommendations are n-.ade: (1) Sodium thiosulfate impregnated glass fiber filters should be used, with an expected improvement in these characteristics: (a) collection efficiency of com- pounds reactive to 03 (e.g., un- saturated compounds); and (b) Tenax GC sorbent stability, which will result in fewer artifact prod- ucts. (2) Selection of the sampling volume must consider the air's humidity (80 to 100% relative humidity), thereby avoiding excessive artifact formation, and, at the same time, early breakthrough for the more volatile components sampled. (3) If the quantities found for benzalde- hyde, acetophenone, and phenol are more than 1,000 no/cartridge, quantitation for these compounds can be conducted. Barbu Demian and Edo D. Pellizzari are with the Research Triangle Institute, Research Triangle Park, NC 27709. Kenneth Krost is the EPA Project Officer (see below). The complete report, entitled "Optimization of GC/MS Based Tenax Collection Method for Toxic Organics," (Order No. PB 83-229 476; Cost: $ 13.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Environmental Sciences Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27717 *US GOVERNNtNT PRINTING OFFICE 1983-659-017/7189 (1) The main artifacts produced from Tenax GC were benzaldehyde, aceto- phenone, phenol, a-hydroxyacetophe- none, acetic acid, and ethylene oxide. ------- United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Postage and F-ees Paid Environmental Protection Agency EPA 335 Official Business Penalty for Private Use $300 PS 0000339 U S ENVIR HROTtCTION AGENCY REGION 5 LIBRAKY 230 S DEARBORN STRtET CHICAGO IL 60604 ------- |