Abstract:

A high performance liquid chromatographic (HPLC) method for multi-residue analysis of phenylurea herbicides in vegetables was developed. The sample was extracted with acetonitrile and cleaned up by solid phase extraction (SPE) using a Florisil cartridge. The target compounds were separated on a C18 column (250 mm×4.6 mm, 5 μm) and detected by a fluorescence detector (FLD) after online post-column ultraviolet (UV) decomposition with a UV lamp with 254 nm wavelength and fluorescent derivatization. The elution gradient, sample pretreatment and conditions of decomposition and derivatization were also studied. The elution gradient was as follows: the mobile phase started with 70%A （water） and 30%B （acetonitrile）, which was increased linearly to 50%B in 15 min, and increased 90%B in the next 15 min and held for 2 min, then returned to the initial conditions in 0.5 min. The column was equilibrated for 10 min at 25 ℃. The flow rate was 0.75 mL/min for HPLC and 0.2 mL/min for derivatization reagent. In the linear ranges of concentrations, the correlation coefficients were between 0.9986 and 1.0000. The 15 herbicides were measured in fortified onion, spinach and cucumber samples at three spiked levels, the average recoveries (n=3) were in the range of 75.3%-121.6% with relative standard deviations of 0.4%-11.6%. The limits of detection (LOD) were 0.005-0.05 mg/kg. The method is simple, sensitive, selective and qualified for phenylurea herbicide multi-residue analysis.

Key words: fluorescent derivatization, online post-column ultraviolet decomposition, phenylurea herbicides, solid phase extraction, vegetables , high performance liquid chromatography (HPLC)