Simultaneous analysis of cocaine and its metabolites in urine by capillary electrophoresis–electrospray mass spectrometry using a pressurized liquid junction nanoflow interface

A new method for the simultaneous separation of cocaine and four metabolites in urine by CE‐ESI‐MS via a pressurized nanoliquid junction interface was developed. The resolution of cocaine, cocaethylene, benzoylecgonine, norcocaine, and ecgonine methyl ester was achieved in a polyvinyl‐alcohol‐coated capillary with 75 μm id × 50 cm total length, using a 15 mM ammonium formate electrolyte solution (pH 9.5) in less than 15 min. In addition, to enhance sensitivity, a field‐amplified sample injection (FASI) was evaluated in terms of injection time and sample solvent composition. The limits of detection achieved with the FASI method ranged from 1.5 to 10 ng/mL for all the compounds. The detection of the studied compounds was performed using an ion‐trap mass spectrometer in a positive ionization mode. A mixture of methanol:water (80:20 v/v) containing 0.1% v/v of formic acid was employed as spray liquid and delivered at ˜200 nL/min. Under optimal CE–MS conditions, linearity was assessed in the concentration range of interest for all analytes with correlation coefficients r 2 ≥ 0.9913. Intra‐ and inter‐day precision provided a relative standard deviation lower than 1.54% for migration times and lower than 12.15% for peak areas. Finally, urine samples, spiked with the standard mixture, were extracted using a solid‐phase extraction procedure and injected under FASI conditions, providing recoveries from 80% to 94% for all analytes.