Rapid differentiation of ortho-, meta-, and para-isomers of halogenated phenylmethylidene hydrazinecarbodithioates by metal complexation and electrospray ionization mass spectrometry.

RATIONALE Development of mass spectrometry (MS)-based methods for isomeric differentiation remains a challenging analytical task, and has attracted the interest of many research groups. It is relevant to develop a general method to differentiate the isomeric halogenated phenylmethylidene hydrazinecarbodithioates (MX, X = F, Cl, Br). METHODS Diluted CH3CN solutions containing NiCl2 and a title isomer (MX) were analyzed by electrospray ionization tandem mass spectrometry (ESI-MSn) in a quadrupole ion trap instrument equipped with an ESI source. Theoretical calculations were performed using the density functional theory (DFT) method at the uB3LYP/6-31+G(2d,p) level. RESULTS In MS3 experiments, the complex [MX + SCH3 + Ni]+ ion, resulting from dissociation of the ESI-generated complex [2MX – H + Ni]+ ion, undergoes ligand-exchange reactions with residual gas molecules, such as water, acetonitrile, and nitrogen in the ion trap, and the o-isomers [Mo-X + SCH3 + Ni]+ were found to undergo the characteristic HX elimination reactions to afford several unique ions. Each set of three isomers [MX + SCH3 + Ni]+ show significantly different reactivity, which has been corroborated by MS4 experiments and theoretical calculations. CONCLUSIONS A rapid method based on metal complexation and tandem mass spectrometric (MSn) analysis has been developed to differentiate three sets of positional isomers of halogenated phenylmethylidene hydrazinecarbodithioates (MX, X = F, Cl, Br). Copyright © 2014 John Wiley & Sons, Ltd.