Determination of Urine Luck in urine using electrospray ionization tandem mass spectrometry

Abstract

A simple, rapid and sensitive method using tandem mass spectrometry (MS-MS) has been developed for the determination of chromate Cr6+ in urine. Cr6+ is a substantial component of Urine Luck, which is used to conceal the presence of drugs in urine. Cr6+ was complexed with diethyldithiocarbamate (DDC) and extracted with isoamyl alcohol in the presence of citric acid. Then a 1-μl aliquot of isoamyl alcohol containing Cr-DDC complex was directly injected into an MS-MS instrument without chromatographic separation. The quantification was performed using selected reaction monitoring at m/z 363.8 of product ion CrO(DDC)2 + obtained by collision-induced dissociation from the precursor ion, CrOH(DDC)3 + at m/z 513.1. This method was validated with the analysis urine samples obtained from volunteers. A linear calibration curve could be obtained in the range of 0.18–100 ng/ml. The limits of detection and quantification of Cr6+ were 0.05 and 0.18 ng/ml, respectively, using only 10 μl of urine. Results could be obtained in less than 10 min for a sample. After oxidation of Cr3+ to Cr6+, near 100% recovery was confirmed using standard reference materials such as SRM 2670a (low level and high level) and SRM 1643e. The most outstanding advantage of this ESI-MS-MS method is that it gives excellent product ion mass spectra for identification of Cr6+.