Abstract:

A method for the determination of ethephon, thidiazuron and diuron in cotton samples has been developed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The sample was extracted with methanol-water. The separation was carried out on a C₈ column (150 mm×4.6 mm, 5 μm) with methanol-water (6:4, v/v) as mobile phase at a flow rate of 0.4 mL/min, and the injection volume was 20 μL. Then the sample solution was analyzed by HPLC-MS/MS in negative ion mode with multiple reaction monitoring (MRM). There were one precursor/two product ion transitions for each pesticide. The results showed that the working curves were linear in the range of 0-10 μg/L for ethephon and thidiazuron, and 0-1 μg/L for diuron. The correlation coefficients (r) were all over 0.999. The limits of quantitation (LOQ) of ethephon, diuron were 40 μg/kg, that of thidiazuron was 4 μg/kg. The average recoveries varied from 89.4% to 100.2% with the relative standard deviations (RSDs) of 5.7%-11.5% at three spiked levels (LOQ, 2LOQ and 4LOQ). The method is simple, rapid and accurate, and can meet the requirements of the domestic and international legislation. The method adapts to confirm the residues of ethephon, thidiazuron and diuron pesticides in cotton samples.

Key words: cotton, diuron, ethephon, high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), thidiazuron