An ionic liquid coating for determination of sildenafil and UK-103,320 in human serum by capillary zone electrophoresis-ion trap mass spectrometry

Abstract

Ionic liquid (IL) was covalently bonded onto the silica capillary surface and the electroosmotic flow was reversed over a pH range of 3.5 to 7. Sildenafil (SL) and its metabolite UK-103,320 (UK) in human serum were detected by solid-phase extraction followed by capillary zone electrophoresis-mass spectrometry analysis. The running buffer contained 10 mM acetic acid adjusted to pH 4.5 with 1 M ammonia, and the separating voltage was set to -25 kV. The adsorption of the analytes onto the bare capillary wall was eliminated by the IL coating and the drugs were baseline-separated within 14 min with detection limits (S/N = 3) of 14 and 17 ng/mL for SL and UK, respectively. The method developed showed good intraday precision in terms of relative standard deviation (RSD) with respect to migration time (RSD ≤ 0.76%, n = 5) and peak area (RSD ≤ 3.4%, n = 5); the relative coefficients of linear regression for both targets were better than 0.99 within linear dynamic range (SL: 50-600 ng/mL; UK: 40-400 ng/mL). Satisfactory interday precision was obtained with respect to the slope of the regression (RSD ≤ 4.21%, n = 9) and the migration time (RSD ≤ 1.1 %, n = 9). The IL coating could be used with stable electroosmotic flow (RSD = 2.78%, n = 10) for at least 80 h.