Determination of Herbicide Residues using LC-MS/MS in Direct Seeded Cultivated Paddy under Drip Irrigation System

A simple, sensitive and cost effective method is reported for the analysis of herbicides by LC-MS/MS with positive spray ionization technique. The limit iof quantification (LOQ) was 0.001 mg kg⁻¹ for pretilachlor and pyrazosulfuron ethyl, 0.002 mg kg⁻¹ for pendimethalin and 0.003 mg kg⁻¹ for bispyribac sodium The calibration curve for each herbicide was linear over the concentration range of 0.01 to 0.1 μg mL⁻¹ and coefficient of determination (R²) was 0.999. Sample extraction was done following the modified QuEChERS technique which recorded recovery within acceptable range of 70–120 per cent for all the herbicides. Residual analysis of the four herbicides following application of pendimethalin, pretilachlor and pyrazosulfuron ethyl (pre-emergent) and bispyribac sodium (post-emergent) in field samples revealed no significant difference between surface drip irrigation and sub-surface drip irrigation systems. Among the treatments, pyrazosulfuron ethyl 10 per cent WP applied at 20 g a.i ha⁻¹ followed by bispyribac sodium 10 per cent SL at 25 g a.i ha⁻¹ recorded the residue of pyrazosulfuron ethyl only in surface and sub -surface drip systems, respectively during 2016 and 2017. Pendimethalin 38.7 per cent CS recorded residues below detectable level; whereas pretilachlor 50 per cent EC applied at 1.0 kg a.i ha⁻¹ did not record any residues in surface and sub-surface drip irrigation systems.