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

Liquid chromatographic (LC) separations for pesticides and many other compounds make use of nonvolatile buffers in the mobile phase. The coupling of LC with mass spectrometry (MS) does not allow the use of nonvolatile buffers. Substitution with volatile buffers is possible, but changes in chromatographic retention and resolution can result even if pH is held constant. The postcolumn removal of nonvolatile buffers using a commercially available ion suppressor is evaluated for the analysis of carbamate pesticides. The suppressor efficiently removes phosphate anions from an LC mobile phase. Most compounds show an increased signal by factors of 2-7 after postcolumn phosphate removal. The suppressor has little effect on the chromatographic parameters of some compounds, while serious negative effects are noted for others. 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 the LC-MS analysis of some pesticides using nonvolatile buffers.