Chiang Mai Journal of Science

A hollow-fiber microextraction (HF-LPME) method was developed for the extraction of four high polarity herbicides (paraquat, diquat, chlormequat, and mepiquat) prior to the analysis by high performance liquid chromatography-mass spectrometry (LC-MS). The miniature extraction system was constructed from a single piece of hollow fiber membrane. Di-(2-ethyl hexyl)phosphoric acid in di-n-hexyl ether was used as membrane supporting liquid. Samples were adjusted to pH 5.0 by a phosphate buffer, and the acceptor solution was HCl pH 0.5. The extracted herbicides were separated on a hydrophilic interaction liquid chromatographic column within 5 minutes using isocratic elution of 10 mM ammonium formate:acetonitrile (50:50). The factors affecting the extraction efficiency were investigated. Under the optimum conditions, the enrichment factors were in the range of 49-476. Excellent linear dynamic range was observed from 2-180 mg/L with correlation coefficients (R2) better than 0.997. Method detection limits were 0.04-0.13 mg/L which are better than values published in the U.S. EPA method 549.2-1. The procedure was validated and tested on water, and rice samples with good success. The method was accurate with recoveries ranging from 71.6 to 78.7%. Good intra-precision and intermediate precision were obtained with RSD lower than 11%.