Quantification of benzene, toluene, ethylbenzene and o-xylene in internal combustion engine exhaust with time-weighted average solid phase microextraction and gas chromatography mass spectrometry

Abstract

A new and simple method for benzene, toluene, ethylbenzene and o-xylene (BTEX) quantification in vehicle exhaust was developed based on diffusion-controlled extraction onto a retracted solid-phase microextraction (SPME) fiber coating. The rationale was to develop a method based on existing and proven SPME technology that is feasible for field adaptation in developing countries. Passive sampling with SPME fiber retracted into the needle extracted nearly two orders of magnitude less mass (n) compared with exposed fiber (outside of needle) and sampling was in a time weighted-averaging (TWA) mode. Both the sampling time (t) and fiber retraction depth (Z) were adjusted to quantify a wider range of Cgas. Extraction and quantification is conducted in a non-equilibrium mode. Effects of Cgas, t, Z and T were tested. In addition, contribution of n extracted by metallic surfaces of needle assembly without SPME coating was studied. Effects of sample storage time on n loss was studied. Retracted TWA-SPME extractions followed the theoretical model. Extracted n of BTEX was proportional to Cgas, t, Dg, T and inversely proportional to Z. Method detection limits were 1.8, 2.7, 2.1 and 5.2 mg m(-3) (0.51, 0.83, 0.66 and 1.62 ppm) for BTEX, respectively. The contribution of extraction onto metallic surfaces was reproducible and influenced by Cgas and t and less so by T and by the Z. The new method was applied to measure BTEX in the exhaust gas of a Ford Crown Victoria 1995 and compared with a whole gas and direct injection method.

Passive Sampling and Analysis of Naphthalene in Internal Combustion Engine Exhaust with Retracted SPME Device and GC-MS

“…It was shown that the TWA model based on Ficks' law works reasonably well for BTEX when the contribution of extraction by metallic parts of the SPME assembly is accounted for [30]. This contribution is reproducible and dependent on the type of compound [30].…”

“…In our previous research, Woolcock et al [37,38], Baimatova et al [30], and Koziel et al [29] addressed these concerns by proposing to use retracted SPME sampling for benzene, toluene, ethylbenzene and o-xylene (BTEX) in hot gas streams from syngas plant, vehicle exhaust, and phenolics, mercaptans and a heterocyclic amine in potentially infectious process reactor air. Baimatova et al [30] and Koziel et al [39] showed that the adsorption to metallic surfaces of SPME assembly is significant, reproducible, yet can be controlled and accounted for. Adsorption to metallic SPME assemblies is likely more of a concern for PAHs but was not assessed before.…”

“…Many methods for long-term monitoring of exposure to environmental pollutants use passive sampling to estimate TWA concentration. The time-weighted averaging (TWA) approach to sampling could be a useful way to "even out" these variations during sampling from vehicle exhaust gases, i.e., a source that is inherently variable [30]. Passive sampling is based on the diffusion of the analyte, either into a large sorbent bed (e.g., passive badges) or onto the retracted SPME fiber.…”

“…This work builds on the development TWA method for determination BTEX in exhaust gases [30] and hot syngas process gas [37,38] with retracted SPME fibers for lower molecular weight compounds. It was shown that the TWA model based on Ficks' law works reasonably well for BTEX when the contribution of extraction by metallic parts of the SPME assembly is accounted for [30].…”

“…Finally, the new method was tested on exhaust gases from idling pickup truck and a tractor and compared side-by-side with a direct injection of sampled exhaust gas method. The working hypotheses were that (a) the contribution of adsorption by metallic SPME assembly parts is reproducible yet significant for naphthalene, a semi-volatile PAH with multiple aromatic rings, and greater than those observed [30] for the mono-aromatic group BTEX group and that (b) naphthalene can be quantified in vehicle exhaust gas using the retracted fiber TWA-SPME approach when the contribution to extraction via SPME metallic parts is accounted.…”