Liquid-phase microextraction and desorption electrospray ionization mass spectrometry for identification and quantification of basic drugs in human urine

Authors


C. Janfelt, Department of Pharmaceutics and Analytical Chemistry, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark.

E-mail: cja@farma.ku.dk

Abstract

Hollow fibre liquid-phase microextraction (LPME) and desorption electrospray ionization mass spectrometry (DESI-MS) were evaluated for the identification and quantification of basic drugs in human urine samples. The selective extraction capabilities of three-phase LPME provided a significant reduction in the matrix effects otherwise observed in direct DESI-MS analysis of urine samples. Aqueous LPME extracts (in 10 mM HCl) were deposited on porous Teflon, dried at room temperature, and the dried spots were then analyzed directly with DESI-MS in full scan mode. Pethidine, diphenhydramine, nortriptyline, and methadone were used as model compounds for identification, and their limits of identification were determined to be 100, 25, 100, and 30 ng/mL, respectively. In a reliability test with 19 spiked urine samples, 100 % of the positive samples containing the model drugs in concentrations at or above the limit of identification were identified. Diphenhydramine was used as a model compound for quantitative analysis with diphenhydramine-d5 as an internal standard. The calibration curve was linear in the range 50–2000 ng/mL (R2 = 0.992) with a limit of quantification at approximately 140 ng/mL. The intra- and inter-day relative standard deviations were <9.5 %. In a reliability test with six spiked urine samples, deviations between the measured and the true values for diphenhydramine were in the range 0.2–22.9 %. Copyright © 2011 John Wiley & Sons, Ltd.

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