Analysis of catechol-type glucuronides in urine samples by liquid chromatography-electrospray ionization-tandem mass spectrometry

A direct and fast liquid chromatographic–electrospray ionization-tandem mass spectrometric (LC–ESI-MS–MS) method is described for the determination of 3-O-glucuronides of E- and Z-entacapone, nitecapone and tolcapone and 1-O- and 2-O-glucuronides of 4-nitrocatechol in urine. p-Nitrophenyl β-d-glucuronide was used as internal standard. Spiked urine samples were prepared by solid-phase extraction and analysed by isocratic LC–ESI-MS–MS in negative ion mode. The ESI mass spectra showed an abundant deprotonated molecule [M–H]−, which was chosen as precursor ion. Collisionally induced dissociation of [M–H]− in MS–MS resulted in the loss of neutral glucuronide moiety and in the appearance of an intense negatively charged drug molecule, which was chosen as the product ion to be monitored in the LC–MS–MS analysis. The new method showed good linearity (r2>0.997) and repeatability of the method (relative standard deviation <2.56%). The limits of detection were determined to be 0.1–0.2 μg/ml when 5 μl of the spiked urine was used for the analysis (5–10 pg of glucuronide introduced to ESI-MS–MS).