Thesis (M.Sc.)--Chulalongkorn University, 2006

A cheap and simple sample preparation technique, hollow fiber supported liquid phase microextraction, was used for the preconcentration of the quaternary ammonium herbicides from drinking water. The cationic herbicides were extracted through a hollow fiber membrane where the supported liquid membrane was 70% di-(2-ethylhexyl) phosphoric acid in di-n-hexyl ether. They were preconcentrated in a few microliters of an acidic acceptor. Liquid chromatography-mass spectrometry was used to analyze these herbicides in only 4-min run time without any ion-pairing agent. The enrichment factors were between 8.9 and 57.2 from a 60-minute extraction. The calibration curve after extraction of 2-10 [micro]g/L spiking level presented the correlation coefficients in the range of 0.97 to 0.99. Relative standard deviations of the % recovery based on ten replicates of 5 and 50 [micro]g/L spiked standard solutions were lower than the % R.S.D. calculated from the Horwitz equation. The method detection limits are 0.17, 0.39, 0.48 and 1.29 [micro]g/L for chlormequat, mepiquat, diquat, and paraquat, respectively. This proposed method was validated and successfully applied for drinking water samples in Thailand with the acceptable % recovery values.