Dissipation and Decontamination of Dimethoate in Curry Leaf using LC-MS/MS (ESI) Technique

Using LC-MS/MS, a method was standardised and validated to estimate dimethoate residues in curry leaf. The LOD and LOQ of 0.001 and 0.002 μg g⁻¹ respectively were observed in the curry leaf matrix. The modified QuEChERS sample extraction procedure using acetonitrile recorded recoveries of 85.71, 104.43 and 83.79 per cent at 0.002, 0.010 and 0.020 μg g⁻¹ spiking level respectively with per cent RSD in the range of 2.13 to 6.36. The RSD values for intra-day and inter-day accuracy tests were found between 3.03 to 10.99 per cent. The results of a supervised field trial with two applications of dimethoate 30 per cent EC at the recommended (200 g a.i. ha⁻¹) and double the recommended (400 g a.i. ha⁻¹) doses recorded initial deposit of 5.747 and 10.383 mg kg⁻¹ respectively which dissipated by more than 99.98 per cent at both the dosages at 30 d after the second application. The calculated half-life values were 3.25 and 3.64 d and safe waiting periods were 34.77 and 42.00 d at the recommended and double the recommended doses, respectively. Different decontamination processes reduced the dimethoate residues in curry leaf in the range of 70.64 to 98.47 per cent. Dipping in 2 per cent salt solution for 15 min followed by boiling for 15 min was found effective and reduced the residues by 98.47 per cent.