Laser-induced electron transfer desorption/ionization on MoO3 and WO3 surfaces for the determination of dithiocarbamates.

Surface layers of molybdenum oxide MoO3 and tungsten oxide WO3 produced by thermal oxidation of molybdenum and tungsten plates in the air were studied for the first time as a platform for laser-induced electron transfer desorption/ionization. High analytical performance of such layers for the determination of metal complexes with dithiocarbamates, such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, and diethyldithiocarbamate, has been demonstrated. All studied complexes are detected as radical cations, with no fragment ions. The ion yields from MoO3 and WO3 surfaces were found to be more than two orders of magnitude higher than those from nanocrystalline silicon surfaces. A novel method has been developed for the determination of trace amounts of dithiocarbamates based on the complexation of analytes with gold ions, followed by laser-induced electron transfer desorption/ionization. The limits of detection of dithiocarbamates were estimated to be about 1 ng/mL. The proposed method was successfully applied to the rapid screening of tetramethylthiuram disulfide residues in juice.