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Abstract

An HPLC method for simultaneous determination of insecticide clothianidin and its metabolites (TZNG, TMG, TZMU, and MNG) in rice was developed and is described in this paper. We extracted the parent clothianidin compound and its metabolites from samples with methanol and an aliquot of the extract was evaporated in a rotary evaporator to remove methanol. The residue was dissolved in 1 mL of 0.005 M 1-sodium octansulfonate (pH 8.3) and transferred to the ENVI-CARB cartridge coupled with an HLB cartridge for solid phase extraction (SPE). Clothianidin and its 4 metabolites were eluted from the cartridges with 3.5 mL of 70% acetonitrile in 0.005 M 1-sodium octansulfonate (pH 7). Determination and separation of clothianidin and its four metabolites were performed in an Agilent Aq column using gradient mobile phase and different UV wavelengths. The average recoveries of clothianidin, TZNG, TMG, TZMU, and MNG were 110%, 87%, 113%, 108%, and 61%, respectively, spiked at 2 ppm into rice. The relative standard deviation (RSD) was determined to be less than 10% in a triple-repeated confirmation test. The limits of quantification (LOQ) were 0.05 ppm for clothianidin, TZNG, TZMU and MNG, and 0.1 ppm for TMG in rice. The method was applied for the determination of clothianidin and its metabolites in 8 polished and 4 unpolished rice grain samples, each of which was collected from a different market in Taiwan. No residue of clothianidin or any of its metabolites was found at levels or at greater than the LOQ in these rice samples.

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