Robust polydimethylsiloxane-polydopamine coated stir bar for rapid extraction of malachite green, crystal violet and their metabolites in aquatic waters and determined by portable mass spectrometry

Triphenylmethane (TPM) fish drug residues and their metabolites exist in many aquiculture waters and can cause significant harm to consumers. Rapid, accurate, and simultaneous detection of their residues in foods is significant in protecting the safety of aquatic products. In the study, a new type of polydopamine coated polydimethylsiloxane (PDMS-PDA) stir bar was prepared for the automatic sorptive extraction and enrichment of malachite green, leucomalachite green, crystal violet, and leucocrystal violet which are common TPM drugs used in aquaculture. The surface of PDMS matrix was first turned to hydrophilic by plasma treatment to enhance the evenness and stability of PDA coating. Therefore, the PDMS-PDA stir bar can enhance its extraction capacity and selectivity towards TPMs. These were due to the synergisitic adsorption capacities of PDA and PDMS towards the dyes. A hand-held stirring device was installed with the stir bar for on-site extraction. After that, a portable mass spectrometer directly detected the eluted targets without chromatography separation. Under the optimized conditions. The four analytes' lower detection limit of 0.16–0.38 μg L^-1 was obtained. Within 35 min, the stir bar device, combing with a portable mass spectrometer, was used for rapid pretreatment and real sample analysis of four analytes with a recovery of 84.3–110 %. All these prove that the assay exhibited potential application prospects for the on-site detection of TPM residues in aquatic waters.