Residue determination of thiamethoxam and its metabolite clothianidin in okra using the modified QuEChERS method with d-SPE clean-up coupled with LC-MS/MS

The aim of this study is to develop a modified QuEChERS method to analyze the thiamethoxam (TMX) and its metabolite clothianidin (CLO) in Okra. Using the developed analytical method the residue level of the neonicotinoid pesticides thiamethoxam (TMX) and its metabolite clothianidin (CLO) was determined in okra. The extraction was carried out using acetate buffer (1.5 g sodium acetate and 3.0 g anhydrous magnesium sulfate) in acetonitrile, and then the extract was cleaned up with optimized dispersive solid phase extraction (d-SPE) sorbents. The method linearity in a wide range (0.001–1.0 mg/L) with (R2≥0.9996), selectivity, accuracy (recoveries in the range of 86.9–97.8 %), precision (relative standard deviation (RSD) ≤ 5.8 %), limit of detection (LOD) and limit of quantification (LOQ) were 0.0007 and 0.002 mg/kg, respectively, and matrix suppression effect (ME) was observed -19.86 and -7.76 % for TMX and CLO, respectively. A total of 100 samples were collected from different market places in Dhaka, Bangladesh. The developed method coupled with LC-MS/MS was applied to determine the residue amount in the collected samples. In 43 % of the samples, TMX residues were found in the range of 0.0051- 0.214 mg/Kg. The maximum residue limit (MRL) of TMX and CLO in okra is 0.010 mg/kg; in 30 % of collected samples, TMX residue exceeds the MRL levels. The residue data were applied to estimate the human health risk.