Quality control in quantification of volatile organic compounds analysed by thermal desorption-gas chromatography-mass spectrometry. J Chromatogr A 1186:348-357

Research Group EnVOC, Department of Organic Chemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium.
Journal of Chromatography A (Impact Factor: 4.17). 05/2008; 1186(1-2):348-57. DOI: 10.1016/j.chroma.2007.11.036
Source: PubMed


This paper presents a detailed study on the calibration of a thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS)-based methodology for quantification of volatile organic compounds (VOCs) in gaseous and liquid samples. For the first time, it is documented to what extent three widely encountered problems affect precise and accurate quantification, and solutions to improve calibration are proposed. The first issue deals with the limited precision in MS quantification, as exemplified by high relative standard deviations (up to 40%, n=5) on response factors of a set of 69 selected VOCs in a volatility range from 16 Pa to 85 kPa at 298 K. The addition of [(2)H(8)]toluene as an internal standard, in gaseous or liquid phase, improves this imprecision by a factor of 5. Second, the matrix in which the standard is dissolved is shown to be highly important towards calibration. Quantification of gaseous VOCs loaded on a sorbent tube using response factors obtained with liquid standards results in systematic deviations of 40-80%. Relative response factors determined by the analysis of sorbent tubes loaded with both analytes and [(2)H(8)]toluene from liquid phase are shown to offer a reliable alternative for quantification of airborne VOCs, without need for expensive and often hardly available gaseous standards. Third, a strategy is proposed involving the determination of a relative response factor being representative for a group of analytes with similar functionalities and electron impact fragmentation patterns. This group method approach indicates to be useful (RSD approximately 10%) for quantifying analytes belonging to that class but having no standards available.

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    • "After conditioning and before sampling, sorbent tubes were loaded with a gaseous internal standard (Tol-d8), separately prepared by making a two-phase system. In short, 500 mL from the headspace of the two-phase system, corresponding to 10.7 ng Tol- d8, was loaded onto each sorbent tube by means of a home-made heated (50 C) injection system flushed with He (100 mL/min) (Demeestere et al., 2008). Before each analytical run, TD-GC-MS was calibrated and the relative sample response factors (RSRF), defined as the ratio of response factor of the compound (peak area/ng loaded on the tube) and the response factor of the internal standard, were calculated for each VOC. "
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