Development and validation of an HPLC-DAD method for the simultaneous determination of most common rice pesticides in paddy water systems

Rice crop is mainly cultivated in large river basins which constitute unique ecosystems and their ecological quality is invaluable. However, the high loads of pesticides used in rice cultivation contribute to the contamination of the water resources in such rice-cultivated regions. To regularly monitor the quality of such water resources there is a need for a rapid and sensitive multi-residue analytical method. This study presents the development and validation of a new analytical method for the simultaneous determination of most rice pesticides including penoxsulam, tricyclazole, propanil and its main metabolite 3,4-dichloroaniline, azoxystrobin, molinate, profoxydim and deltamethrin. A solid-phase extraction (SPE) procedure followed by high performance liquid chromatography (HPLC) with diode array detection (DAD) was used. A C-18 RP column operated at 30 degrees C was utilised and the analytes were separated with a mobile phase of acetonitrile/water mixture in a linear gradient. Clean-up of water samples and isolation of pesticides was performed on SPE Bakerbond octadecyl cartridges and an ethyl acetate-dichlomethane mixture (9 : 1 v/v, 2 mL) was used for elution. Method validation was performed by means of intra-day (n = 5) and inter-day accuracy and precision (n 8), sensitivity and linearity. The relative recoveries of the pesticides in paddy water samples were acceptable (80.6-110.2%) and the relative standard deviation (RSD%) ranged from 1.9 to 7.6%. Limits of detection (LOD) and limits of quantification (LOQ) varied from 0.1 to 0.8 ng mL(-1) and 0.25 to 2.0 ng mL(-1) respectively, depending on the analyte. The method was subsequently applied for the determination of pesticide residues in paddy and canal water samples. Tricyclazole was the most frequently detected pesticide at the highest concentrations, while herbicides were less frequently detected and at lower concentrations. The method described could be a valuable tool for regular monitoring of surface water systems in rice-cultivated basins.