Determination of the insecticide imidacloprid in potato (Solanum. tuberosum L.) and onion (Allium cepa) by high-performance liquid chromatography with diode-array detection

A high-performance liquid chromatography (HPLC) method has been proposed for the determination of imidacloprid residues in fortified potato (Solanum tuberosum L.) and onion (Allium cepa) and in treated potato and onion samples. Sample preparation consisted of dichloromethane extraction of imidacloprid from the plant material, followed by purification of the obtained onion extract on an LC-Florisil disposable cartridge. The obtained potato extracts were further analyzed without purification. The HPLC-diode-array-detection (DAD) method has been developed on reversed phase for separation of imidacloprid with isocratic elution with a mixture of 0.01 M phosphate buffer (pH 3.15) and acetonitrile (75 : 25, v/v). Spectral data obtained with DAD allow the identification of imidacloprid residue. Detector response showed a linear dynamic range from 0.0125 to 0.500 mu g/mL. Imidacloprid was recovered from fortified samples in a range of 94-99%. The within-day RSD of repeatability of the retention time of imidacloprid standard solution was less than 0.1% and of the obtained peak area less than 5%. For potato and onion samples, the limits of detection were 0.0075 and 0.0060 mg/kg and the limits of determination were 0.015 and 0.012 mg/kg, respectively.