Objective  While detecting the concentration of organophosphorus pesticides in natural water by ultraviolet-visible absorption spectroscopy method, the detection accuracy was easily interfered by the turbidity caused by suspended solids in the natural water, therefore the natural water containing organophosphorus pesticides was needed to be pretreated (filtered) before detection. This paper studied the effects of different filtration conditions on the absorption spectra and concentration prediction models of organophosphorus pesticides in natural water.

Method  Methyl parathion was selected as the research object, meanwhile pond water, farmland water and canal water were used as diluents to prepare experimental samples with different concentration gradients. The study used 400 mesh (40 μm pore size) gauze, 5 μm filter membrane, 0.45 μm filter membrane to filter three kinds of natural water-organophosphorus pesticide solutions respectively, and used the turbidity sensor to detect the turbidity of natural water before and after filtration. The ultraviolet-visible absorption spectroscopy detection system was built to obtain the spectrum data of experimental sample before and after filtration, combining with chemometric methods to construct quantitative prediction models for methyl parathion.

Result  The turbidity of three kinds of natural water obviously decreased after filtration by 5 and 0.45 μm filter membranes. Methyl parathion had only two characteristic peaks in three kinds of natural water, which were located at about 225 and 275 nm respectively in samples with all tested mass concentrations before and after filtering by different filtration conditions. On the whole, filtration enhanced the linear relationship between the concentration and optical density of methyl parathion solutions, the filtered natural water-methyl parathion solution spectra models had high prediction accuracy and could be used for quantitative analysis. Among three filtration conditions used in this study, the 5 μm filter membrane had the best filtration effect, which could remove the turbidity disturbance and the organophosphorus pesticides spectra model had high prediction accuracy.

Conclusion  The filtered models of methyl parathion have less turbidity interference and are more suitable for practical application detection. This study provides a theoretical basis for pretreatment of rapid detection of organophosphorus pesticide concentration in natural water by ultraviolet-visible absorption spectroscopy.