VA Medical Center-113, San Diego, CA 92161 and Dept. of Pathology, UCSD, USA

The standard REMEDi mobile phase was changed to an ammonium acetate/acetonitrile mix to make it compatible with positive ion electrospray ionization. Sample preparation consisted of adding 200 uL of the REMEDi internal standard mixture (an ammonium acetate buffer containing retention time markers) to 1 mL of urine. After centrifugation to pellet out any solids present, samples were automatically injected into the REMEDi which had been interfaced with an ion trap mass spectrometer (Finnigan LCQ).

The REMEDi/MS system detected 18 drugs from a variety of classes including amphetamines, benzoylecgonine, antidepressants, benzodiazepines, opiates and antihistamines directly from urine specimens using both a full scan mode and a data dependant MS/MS mode of analysis. The ion trap was under automatic gain control with full scan and MS/MS targets of 5 x 10⁷ and 2 x 10⁷ respectively. In the data dependant mode, the LCQ collected full scan spectra from 50 to 500 amu and when any ion exceeded 1 x 10⁶ counts, it automatically switched to collect daughter ion spectra. With electrospray ionization most drugs only exhibit a molecular ion in the full scan mode, consequently MS/MS is necessary for unequivocal identification.

The quantitative ability of this system was demonstrated for the cocaine metabolite benzoylecgonine (BE) using benzoylecgonine-d₃ as the internal standard. Quantification was performed using selected reaction monitoring. The parent/daughter ions for benzoylecgonine and benzoylecgonine-d₃ were 290/168 and 293/171 respectively. Using 200 ng/mL benzoylecgonine-d₃ as the internal standard the method was linear from 30 to 10,000 ng/mL (r squared = 0.999).