Determination of lewisite metabolite 2-chlorovinylarsonous acid in urine by use of dispersive derivatization liquid-liquid microextraction followed by gas chromatography-mass spectrometry.
The purpose of this study was to develop a sensitive and simple method, based on dispersive derivatization liquid-liquid microextraction-gas chromatography-mass spectrometry (DDLLME-GC-MS) in scanning and selected-ion-monitoring (SIM) modes, for detection of 2-chlorovinylarsonous acid (CVAA) as a hydrolysis product and urinary metabolite of lewisite in urine samples. Chloroform (65 μL), methanol (500 μL), and ethanedithiol (10 μL) were used as extraction solvent, dispersive solvent, and derivatizing reagent, respectively. Critical conditions of the proposed method were optimized. The nucleophilic reactions of dithiol and monothiol compounds with CVAA were also studied using a competitive method. In view of the high affinity of trivalent arsenic for sulfhydryl groups, the interaction between CVAA and bis(2-chlorovinyl)arsonous acid (BCVAA) and free cysteine (Cys) was also investigated using liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS). The interference of Cys, present in human urine, with the detection of CVAA was evaluated using dithiol and monothiol chemicals as derivatization agents. The developed method provided a preconcentration factor of 250, and limits of detection of 0.015 and 0.30 μg L(-1) in SIM and scanning modes, respectively. The calibration curves were linear over the concentration range of 1-400 μg L(-1) in full-scan mode. The relative standard deviation (RSD) values were calculated to be 5.5 and 3.2% at concentrations of 20 and 100 μg L(-1), respectively. Collision-induced dissociation studies of the major electron-impact (EI) ions were performed to confirm the proposed fragment structure of CVAA-dithiols derivatives. Results indicated that the developed method for analysis of CVAA is suitable not only for verification of human exposure to lewisite, but also for quantification of CVAA in urine samples.