Identification of photochemical methylation products of tin(ii) in aqueous solutions using headspace SPME coupled with GC-FPD or GC–MS

Methylation is an important transformation process for elements in the environment. Herein, headspace solid phase micro-extraction (HP-SPME) coupled with gas chromatography–flame photometric detection (GC-FPD) or gas chromatography–mass spectrometry (GC–MS) techniques were employed to study the photochemical methylation of inorganic tin(II) by eight organic compounds (including acetone, pyruvic acid, acetic acid, propionic acid, dimethyl sulfoxide, N,N-dimethylformamide, tert-butyl alcohol and isopropyl alcohol) in aqueous solutions. The major products were identified as monomethyltin (MMT) and dimethyltin (DMT), as well as trimethyltin (TMT) as the minor product. The yields of methyltin products were closely related to the chemical structures of methyl donors, and the pH and salinity of the reaction solution. The concentrations of methyltin products peaked at a pH of 5.0 and a salinity of 0.5 M. The dominating product also changed from MMT to DMT with an increase in pH value. Notably, pyruvic acid can readily methylate tin(II) under irradiation by sunlight in view of its absorption of sunlight, demonstrating that photochemical methylation is a possible transformation pathway for tin(II) in the environment.