Automated on-line in-tube solid-phase microextraction followed by liquid chromatography/electrospray ionization-mass spectrometry for the determination of chlorinated phenoxy acid herbicides in environmental waters

A method for the determination of six chlorinated phenoxy acid herbicides in river water was developed using in-tube solid-phase microextraction (SPME) followed by liquid chromatography/electrospray ionization-mass spectrometry (LC/ESI-MS). In-tube SPME is an extraction technique for organic compounds in aqueous samples, in which analytes are extracted from a sample directly into an open tubular capillary by repeated draw/eject cycles of the sample solution. Simple mass spectra with strong signals corresponding to [M-H](-) and [M-RCOOH](-) were observed for all herbicides tested in this study. The best separation of these compounds was obtained with a C(18) column using linear gradient elution with a mobile phase of acetonitrile-water containing 5 mmol l(-1) dibutylamine acetate (DBA). To optimize the extraction of herbicides, several in-tube SPME parameters were examined. The optimum extraction conditions were 25 draw/eject cycles of 30 mul of sample in 0.2% formic acid (pH 2) at a flow rate of 200 mul min(-1) using a DB-WAX capillary. The herbicides extracted by the capillary were easily desorbed by 10 mul acetonitrile. Using in-tube SPME-LC/ESI-MS with time-scheduled selected ion monitoring, the calibration curves of herbicides were linear in the range 0.05-50 ng ml(-1) with correlation coefficients above 0.999. This method was successfully applied to the analysis of river water samples without interference peaks. The limit of quantification was in the range 0.02-0.06 ng ml(-1) and the limit of detection (S/N = 3) was in the range 0.005-0.03 ng ml(-1). The repeatability and reproducibility were in the range 2.5-4.1% and 6.2-9.1%, respectively.