Demeestere Kristof, Dewulf Jo, De Roo Karlien, De Wispelaere Patrick, Van Langenhove Herman
Research Group EnVOC, Department of Organic Chemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium.
J Chromatogr A. 2008 Apr 4;1186(1-2):348-57. doi: 10.1016/j.chroma.2007.11.036. Epub 2007 Nov 19.
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.
本文详细研究了基于热脱附-气相色谱-质谱联用（TD-GC-MS）技术对气态和液态样品中挥发性有机化合物（VOCs）进行定量分析的校准方法。首次记录了三个常见问题对精确定量的影响程度，并提出了改进校准的解决方案。第一个问题涉及质谱定量的精度有限，例如在298K下，一组69种选定VOCs的响应因子的相对标准偏差较高（高达40%，n = 5），其蒸气压范围为16Pa至85kPa。在气相或液相中添加[(2)H(8)]甲苯作为内标，可将这种不精确性降低5倍。其次，标准物质溶解于其中的基质对校准至关重要。使用液相标准物质获得的响应因子对吸附管上负载的气态VOCs进行定量，会导致40%-80%的系统偏差。通过分析负载有分析物和[(2)H(8)]甲苯的吸附管，从液相中测定相对响应因子，可提供一种可靠的替代方法来定量空气中的VOCs，而无需使用昂贵且通常难以获得的气态标准物质。第三，提出了一种策略，即确定一个相对响应因子，该因子代表一组具有相似官能团和电子轰击碎片模式的分析物。这种分组方法对于定量属于该类但没有标准物质可用的分析物很有用（相对标准偏差约为10%）。
