Microemulsion electrokinetic chromatography with on-line atmospheric pressure photoionization-mass spectrometric detection of medium polarity compounds

In this paper, we present the determination of pharmaceuticals employing microemulsion electrokinetic chromatography (MEEKC) with atmospheric pressure photoionization-mass spectrometric (APPI-MS) detection. This recent hyphenated technique allows to overcome some disadvantages of MEEKC, namely its inherent incompatibility with MS detection. Important parameters like microemulsion (ME) composition, the composition of the sheath liquid and APPI-MS detection parameters have been investigated. Using the optimized set of parameters, the eight selected substances could be detected down to concentrations between 3 mg L−1 (phenacetin) and 41 mg L−1 (diltiazem). Switching to the MS2 mode, the use of specific transitions for the detection of each analyte provided improved detection limits in the range of 0.6 mg L−1 (carbamazepine) to 6 mg L−1 (metoprolol). Calibration curves were linear over one to two orders of magnitude with correlation coefficients better than 0.98.