Rapid screening of doping agents in human urine by vacuum MALDI-linear ion trap mass spectrometry

Detection of doping agents in urine frequently requires extensive separation prior to chemical analyses. Gas or liquid chromatography coupled to mass spectrometry has produced accurate and sensitive assays, but chromatographic separations require time and, sometimes, chemical derivatization. To avoid such tedious and lengthy procedures, vacuum matrix-assisted laser desorption ionization (vMALDI) coupled with the linear ion trap mass spectrometry (LIT/MS) technique is tested for its applicability as a rapid screening technique. Commonly used doping agents like nandrolone, boldenone, trenbolone, testosterone, and betamethasone were chosen as study compounds. Different MALDI matrixes like alpha-cyano-4-hydroxycinnamic acid (CHCA), dibyroxy benzoic acid (DHB) with and without cetyl trimethyl ammonium bromide (CTAB), a surfactant, and meso-tetrakis(pentafluorophenyl) porphyrin (F20TPP) were tested. Among them, F20TPP (MW 974.57 Da) was selected as the preferred matrix owing to the lack of interfering matrix peaks at the lower mass range (m/z 100-700). Urine samples spiked with study compounds were processed by solid-phase extraction (SPE) and consistently detected through a linear range of 0.1-100 ng/mL. The limit of detection and lower limit of quantification for all five analytes have been determined to be 0.03 and 0.1 ng/mL, respectively, in urine samples. Testosterone-d(3) was used as an internal standard, and the quantitative measurements were achieved by the selective reaction monitoring (SRM) mode. The method was validated and showed consistency in the results. Hence, vMALDI-LIT/MS can be used as a rapid screening method to complement the traditional GC/MS and LC/MS techniques for simultaneous identification, confirmation, and quantification of doping agents in urine.