Solid phase microextraction combined with gas chromatography-mass spectrometry for the determination of diquat residues in water

A novel method for the determination of diquat in aqueous samples was developed and applied to environmental water samples. The method involved sodium borohydride-nickel chloride (NaBH4-NiCl2) reduction and headspace solid phase microextraction (HS-SPME) of the perhydrogenated products. Gas chromatography-mass spectrometry was used to identify and quantify the analytes in selected ion monitoring (SIM) mode. The parameters and variables that affected the reduction and extraction were also investigated. The optimal conditions for the reduction were found to be 20 mg NaBH4, 200 μL 10% of NiCl2 (w/v) and heating at 90°C for 10 min. For the extraction, the SPME fiber was exposed for 20 min at 60°C. Using these conditions, the recovery rates of diquat ranged from 92.59 to 101.27% in water. Good linearity (y = 0.0769x + 0.2748, r2 = 0.999) was obtained, intra- and inter-day precision were less than 3.99 and 5.64%, respectively. We found that reduzates of diquat exist as cis- and trans-isomers, and their ratio is 1: 5.3, with RSD of 13.1% (n = 17).