Static headspace sampling followed by gas chromatography and gas chromatograhy-mass spectrometry applied to various complex matrices

Date of Completion

January 1999

Keywords

Chemistry, Analytical|Environmental Sciences

Degree

Ph.D.

Abstract

Static headspace sampling was studied to: (1) minimize the effect of a soil's matrix on the analysis of benzene, toluene, ethylbenzene, and xylenes from soils, (2) determine the Henry's law coefficients for various fuel components, (3) compare gas-sampled and solid phase microextraction (SPME)-sampled static headspace, and (4) successfully couple static headspace sampling to high-speed GC. ^ The effects of various matrix modifiers were studied in addition to alternative techniques such as the full evaporation technique, to determine an effective way to eliminate the effect of the matrix on analyte recovery. The full evaporation technique used very high temperatures to force the analytes of interest into the gaseous phase. Using these high temperatures and no matrix modifying solution provided an analysis free of matrix effects. ^ Henry's Law coefficients were determined for several compounds found in reformulated gasolines. This new method relies only on the knowledge of the phase ratio defined by the experimental apparatus. The value obtained for MTBE using the method was in excellent agreement with other literature values, specifically 1.7 M/atm. Other compounds studied included: ETBE, TAME, DIPE, benzene, toluene, and ethylbenzene. ^ The comparison of gas-sampled and SPME-sampled static headspace methods when applied to GC-MS analyses was examined for the effectiveness of transferring of volatile components of several juices from sample vial to chromatograph. The results of this study showed the SPME fiber to be approximately 1400 time more effective, owing to the ability of the fiber to concentrate the analytes and transfer them without the need to inject large volumes of inert gas into the instrument. ^ Finally, the coupling of static headspace to high-speed GC allowed the reduction of the analysis time reported in the SPME study by a factor of approximately twenty times, from 75 to just 4 minutes. The sampling system designed used batch equilibration of many samples to enhance the speed of analysis, in conjunction with a sample collection method that used a trapping column to collect the sample which is rapidly transferred from the sample vial to the instrument by a stream of nitrogen. ^

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