EVALUATION OF GAS-CHROMATOGRAPHY MATRIX-ISOLATION INFRARED SPECTROMETRY FOR THE DETERMINATION OF SEMIVOLATILE ORGANIC-COMPOUNDS IN AIR SAMPLE EXTRACTS

The capabilities of gas chromatography/matrix isolation infrared (GC/MIIR) spectrometry for the determination of semivolatide organic compounds (SVOCs) in environmental air sample extracts were evaluated. A series of systematic experiments, using the xylene isomers as test compounds, was conducted to determine the repeatability of the various steps involved in GC/MIIR measurements and to identify parameters which affect the precision in quantitative analyses. The repeatability of MIIR net absorbance measurements for both single and replicate depositions was determined. The precision for MIIR net absorbance measurements on single depositions was found to be better than 2%, whereas measurements for daily replicate depositions had relative standard deviations of less than 4%. The effect of experimental parameters, such as deposition tip position and cryogenic disk time resolution, on the overall precision is illustrated. The detection limits and range of linear response of the GC/MIIR method for o-, m-, and p-xylene were determined by analyzing calibration standards ranging in concentration from 0.87 to 86.9 ng/mu-L. The MIIR net absorbance exhibited a nonlinear response at concentrations higher than 52.1 ng/mu-L, which was most likely due to an increase in the sample spot size relative to the IR beam focus or a decrease in the matrix-to-solute ratio to less than what is acceptable for matrix isolation conditions. The method detection limit for the xylene isomers was estimated to be between 1 and 2 ng/mu-L injected on-column for routine measurements. Extensive signal averaging was required to obtain identifiable spectra at concentrations less than 1 ng/mu-L. The GC/MIIR method was tested by determining target SVOCs in amblent air sample extracts. The MIIR quantitative results were compared to those obtained on the system's flame ionization detector (FID). The FID response exhibited a high bias when unknown compounds coeluted with a target analyte. The ability of GC/MIIR to quantify target compounds in the presence of interferents and to discriminate between coeluting isomers is demonstrated. Overall, the GC/MIIR technique provided excellent quantitative data. However, because of the complexity of the equipment and the time required for analysis, the current method is not amenable to routine measurements.