Analysis of pesticides by LC-electrospray-MS with postcolumn removal of nonvolatile buffers

Liquid chromatographic (LC) separations for pesticides and many other compo unds make use of nonvolatile buffers in the mobile phase. The coupling of L C with mass spectrometry (MS) does not allow the use of nonvolatile buffers . Substitution with volatile buffers is possible, but changes in chromatogr aphic retention and resolution can result even if pH is held constant. The postcolumn removal of nonvolatile buffers using a commercially available io n suppressor is evaluated for the analysis of carbamate pesticides. The sup pressor efficiently removes phosphate anions from an LC mobile phase. Most compounds show an increased signal by factors of 2-7 after postcolumn phosp hate removal. The suppressor has little effect on the chromatographic param eters of some compounds, while serious negative effects are noted for other s. Some compounds will give poor results due to adsorption or retention by the suppressor. The results indicate that such a device may be useful for t he LC-MS analysis of some pesticides using nonvolatile buffers.