Study on the Derivatization Process Using N-O-bis-(trimethylsilyl)-trifluoroacetamide,N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide, Trimethylsilydiazomethane for the Determination of Fecal Sterols by Gas Chromatography-Mass Spectrometry

Fecal sterol has been proposed as a chemical indicator of human fecal pollution even when fecal coliform populations have diminished due to water chlorination or toxic effects of industrial effluents. This paper describes an improved derivatization procedure for simultaneous determination of four fecal sterols including coprostanol, epicholestanol, cholesterol and cholestanol using gas chromatography-mass spectrometry (GC-MS), via optimization study on silylation procedures using N-O-bis (trimethylsilyl)-trifluoroacetamide (BSTFA), and N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA), which lead to the formation of trimethylsilyl (TMS) and tert-butyldimethylsilyl (TBS) derivatives, respectively. Two derivatization processes of injection-port derivatization and water bath derivatization (60 C, 1h) were inspected and compared. Furthermore, the methylation procedure at 25 C for 2h with trimethylsilydiazomethane (TMSD) for fecal sterols analysis was also studied. It was found that most of TMS derivatives demonstrated the highest sensitivities, followed by methylated derivatives. For BSTFA or MTBSTFA derivatization processes, the simple injection-port derivatization process could achieve the same efficiency as that in the tedious water bath derivatization procedure. Keywords—Fecal Sterols, Methylation, Silylation, BSTFA, MTBSTFA, TMSD, GC-MS. Manuscript received August 15, 2008. This work was supported by the Incentive for Research & Innovation Scheme (IRIS) under Grant IRIS-031-00 from Environment & Water Industry Development Council (EWI), Singapore. Jingming Wu is with the Center for Advanced Water Technology, PUB Consultants, the Toh Tuck Complex, 80/82, Toh Guan Road East, Singapore 608575 (e-mail: [email protected]). Ruikang Hu is with the Center for Advanced Water Technology, PUB Consultants, the Toh Tuck Complex, 80/82, Toh Guan Road East, Singapore 608575 (e-mail: [email protected] ). Junqi Yue is with the Center for Advanced Water Technology, PUB Consultants, the Toh Tuck Complex, 80/82, Toh Guan Road East, Singapore 608575 (e-mail: [email protected]). Zhaoguang Yang is with the Center for Advanced Water Technology, PUB Consultants, the Toh Tuck Complex, 80/82, Toh Guan Road East, Singapore 608575 (e-mail: [email protected]). Lifeng Zhang (corresponding author) is with the Center for Advanced Water Technology, PUB Consultants, the Toh Tuck Complex, 80/82, Toh Guan Road East, Singapore 608575 (phone: +65-6326-2931; fax: +65-6326-2936. E-mail: [email protected]).