CEC-ESI ion trap MS of multiple drugs of abuse

This article describes a method for the separation and determination of nine drugs of abuse in human urine, including amphetamines, cocaine, codeine, heroin and morphine. This method was based on SPE on a strong cation exchange cartridge followed by CEC-MS. The CEC experiments were performed in fused silica capillaries (100 m×30 cm) packed with a 3 m cyano derivatized silica stationary phase. A laboratory-made liquid junction interface was used for CEC-MS coupling. The outlet capillary column was connected with an emitter tip that was positioned in front of the MS orifice. A stable electrospray was produced at nanoliter per minute flow rates applying a hydrostatic pressure (few kPa) to the interface. The coupling of packed CEC columns with mass spectrometer as detector, using a liquid junction interface, provided several advantages such as better sensitivity, low dead volume and independent control of the conditions used for CEC separation and ESI analysis. For this purpose, preliminary experiments were carried out in CEC-UV to optimize the proper mobile phase for CEC analysis. Good separation efficiency was achieved for almost all compounds, using a mixture containing ACN and 25 mM ammonium formate buffer at pH 3 (30:70, v/v), as mobile phase and applying a voltage of 12 kV. ESI ion-trap MS detection was performed in the positive ionization mode. A spray liquid, composed by methanol-water (80:20, v/v) and 1% formic acid, was delivered at a nano-flow rate of 200 nL/min. Under optimized CEC-ESI-MS conditions, separation of the investigated drugs was performed within 13 min. CEC-MS and CEC-MS2 spectra were obtained by providing the unambiguous confirmation of these drugs in urine samples. Method precision was determined with RSDs values 3.3% for retention times and 16.3% for peak areas in both intra-day and day-to-day experiments. LODs were established between 0.78 and 3.12 ng/mL for all compounds. Linearity was satisfactory in the concentration range of interest for all compounds (r20.995). The developed CEC-MS method was then applied to the analysis of drugs of abuse in spiked urine samples, obtaining recovery data in the range 80-95%.