NEW APPROACH FOR THE ANALYSIS OF ACIDIC PESTICIDES IN WATER BY LC/MS WITH A PARTICLE-BEAM INTERFACE

A new method for the determination of 18 acidic pesticides in water by liquid chromatography/mass spectrometry is presented. A liquid-solid extraction procedure for the isolation of the pesticides from the aqueous samples was employed. The method, which avails of a micro-flow rate particle beam interface, offers improved performance far the analysis of heat-sensitive compounds such as phenoxy acid herbicides. The new technique combines the benefits of a reduced mobile-phase flow rate (1-5 mu L/min) with a modified vaporization surface inside the ion source of the mass spectrometer. The electron impact ion source was covered with a Teflon layer, which has been proven to minimize compounds' decomposition and adsorption. The improved vaporization of thermally unstable substances, accomplished by the modified surface, allows a higher signal response and an accurate reproduction of the original chromatographic profile. Electron impact ionization allows almost unambiguous identification of the analytes. The liquid chromatography, carried out with a C18 packed capillary column, was optimized to allow the injection of larger sample volumes, thus improving method sensitivity for trace level pollutants. The detection limits were in the range of 0.1-1 ppb, which is a considerable improvement in the analysis of these compounds with mass spectrometric detectors.