Capillary electrophoresis-tandem mass spectrometry combined with molecularly imprinted solid phase extraction as useful tool for the monitoring of 5-nitroimidazoles and their metabolites in urine samples

A novel capillary electrophoresis-tandem mass spectrometry approach is proposed for the determination of eleven 5-nitroimidazoles in urine samples for therapeutical drug monitoring purposes. A comparison between two separation modes, namely micellar electrokinetic chromatography and capillary zone electrophoresis was carried out, obtaining higher selectivity when 1 M formic acid (pH 1.8) was selected as background electrolyte. 5-Nitroimidazoles were hydrodynamically injected in water for 40 s at 50 mbar and their separation was performed at 28 kV and 25 degrees C. To improve migration time repeatability, a pressure of 50 mbar was applied to the inlet vial during runs without any loss of peak resolution. Electrospray ionization parameters were established as follow: 6 L/min, dry gas flow rate; 51,021.2 Pa, nebulization pressure; 160 degrees C, dry gas temperature. Sheath liquid consisted of a mixture of propan-2-ol/water/acetic acid (60.0:38.8:0.2% v/v/v) supplied at 3.3 mu L/min. MS parameters were optimized for analyte identification through their MS2 and MS3 spectra. The method was applied to the determination of 5-nitroimidazoles in urine samples, applying molecularly imprinted solid phase extraction for sample clean-up. Recoveries higher than 79.2% demonstrated the suitability of the procedure. Limits of detection ranged from 9.6 to 130.2 mu g/L while precision assays resulted in relative standard deviations for peak areas lower than 16.1%.