Large volume injection of acidic pesticides by reversed-phase micro high-performance liquid chromatography

Modern liquid chromatography-mass spectrometry interfaces often require a limited intake of mobile phase to work properly. Packed capillary columns combine high chromatographic efficiency, reduced flow-rate and an appreciable reliability and can be successfully employed in such applications. Acidic pesticides, a group of important compounds widely used in agriculture and often encountered as environmental pollutants, are positively analyzed by reversed-phase HPLC. The combination of micro-HPLC and particle beam mass spectrometry offer a powerful tool for their determination at very low concentrations. However, any detection limit obtained by this instrumentation is impaired by the constraint of a very small injection volume compatible with a narrow-bore column. In this paper, a procedure based on large volume injection is presented. This procedure is capable of increasing up to 800 times the volume of sample that can be injected into a packed capillary column. Seventeen acidic pesticides were selected for this study representing most of the compound classes commonly found in several environmental matrices. This method differs from previous attempts because of the acidic dissociation in water which may interfere with a correct solute focusing. The larger sample availability consistently improved the method sensitivity based on a LC-MS technique.