Capillary isotachophoresis with ESI-MS detection: Methodology for highly sensitive analysis of ibuprofen and diclofenac in waters

The possibilities of reaching higher sensitivity in capillary electrophoretic analyses of complex samples with ESI-MS detection were investigated on the example of analysis of diclofenac and ibuprofen in waters. The applied separation approach is based on application of isotachophoresis that ensures permanent stacking of analytes until they reach the detector. Investigation of the possibilities of MS detector optimization have shown that optimization of fragmentor voltage and working in the SIM mode with collection of data for multiple fragments both increases the method specificity and approx. doubles its sensitivity. Combination with an offline SPE preconcentration step resulted in very high sensitivity of the described methodology with a reached LOD below 2 × 10⁻¹² M, corresponding to analyte levels of 0.6 ng L⁻¹ of diclofenac and 0.4 ng L⁻¹ of ibuprofen. The results demonstrate that CE-MS, particularly when performed in the ITP mode, has the potential to reach sensitivities comparable to HPLC-MS.