Penicillin analyses by capillary electrochromatography-mass spectrometry with different charged poly(stearyl methacrylate–divinylbenzene) monoliths as stationary phases

This study describes the ability of an on-line concentration capillary electrochromatography (CEC) coupled with mass spectrometry (MS) for the determination of eight common penicillin antibiotics. Poly(stearyl methacrylate–divinylbenzene) (poly(SMA–DVB)) based monolithic columns prepared under the same conditions but differing only in the charged monomer were used as separation columns. Vinylbenzyl trimethylammonium chloride (VBTA) and vinylbenzenesulfonate (VBSA) were employed as the positively charged monolith and negatively charged monolith, respectively. Results indicated that poly(SMA–DVB–VBTA) monolithic column provided reproducible performance for penicillin separation through ion-exchange interaction, while the negatively charged poly(SMA–DVB–VBSA) column produced unstable separation due to the electrostatic repulsion between the electrophilic analytes and the negatively charged stationary phase. On-line concentration steps of step-gradient elution combined with anion selective injection (ASEI) were used to enhance the detection sensitivity of the CEC-MS method and all penicillin detection sensitivities were further improved (reduction in the limits of detection from 1.9–31 μg/L (normal injection mode) to 0.05–0.2 μg/L (on-line concentration mode)). Finally, this optimal on-line concentration CEC-MS method was applied to trace penicillin analyses in milk samples.