Abstract
We developed a simple colorimetric method which can separately determine paraquat and diquat utilizing automatic reduction property of diquat under existence of tetramethylammonium hydroxide. In the first step, diquat in the sample was automatically reduced by adding tetramethylammonium hydroxide, and UV/VIS spectrum (λmax=430 nm) and absorbance at 430 nm were measured for confirmation and determination of diquat. In the second step, paraquat in the sample was also reduced by adding sodium hydrosulfite, and UV/VIS spectrum (λmax=396 nm, 600 nm.) and absorbance at 600 nm were measured for confirmation and determination of paraquat. The calibration curves were linear in the concentration range from 1-100 ppm for both compounds. The herbicide containing both paraquat and diquat, Preeglox-L®, showed typical UV/VIS spectra of each compound, and there was a good correlation between herbicide concentration and paraquat and diquat concentrations. The established method was successfully applied to forensic samples, gastric content and heeltap solution.
