A STUDY OF RELATIVE PERFORMANCE BETWEEN DIRECT INJECTION AND THERMAL DESORPTION FOR SEVERAL VOLATILE ORGANIC ACIDS AND REFERENCE VOCS BY GAS CHROMATOGRAPHY - MASS SPECTROMETRY

Abstract

In this research, the relative performance of gas chromatography - mass spectrometry (GC-MS) has been examined to compare the recovery rates (RR) obtained for several volatile organic acids in air when using different sample introduction methods. To this end, a comparison was performed between direct injection (DI) and thermal desorption (TD) for introduction of the samples into the GC-MS. The GC-MS system was calibrated initially by using liquid phase working standards (L-WS) comprising a mixture of 13 volatile organic compounds (VOCs) with a main emphasis on volatile organic acids and several reference compounds including aromatics with and without the use of TD. Assuming that one can acquire the optimum sensitivity for any given individual compound by direct injection (DI: i.e., without TD), the response factors (RF) derived by the DI method are compared against those of TD on a compound-by-compound basis to assess the relative sensitivity attributable to the two methods. To this end, the RF values are adjusted for each VOC and each of the two different approaches by considering the different split ratios for TD and DI. According to this comparison, the RR of the TD method tends to vary with target compound; however, a RR near unity is attained for most VOCs except for MEK and organic acids.