Determination of Profenofos Residues using LC-MS/MS and Its Dissipation Kinetics in Pigeonpea Pods

Abstract

Background: Pigeonpea is a drought resistant legume crop, cultivated in semiarid tropical and subtropical regions of the world mainly for its protein enriched seeds. Insect pests are major biotic constraints implicating yield losses of staggering dimensions. Profenofos is being used for management of pigeonpea pod borer and studying the pattern of dissipation, residual occurrence and hazard index for consumption of pigeonpea grain contaminated with profenofos is very important. Methods: A simple, sensitive and reproducible method for analysis of profenofos in pigeonpea green pods and dry grain was standardized and validated using liquid chromatography tandem mass spectrometry (LC-MS/MS) with electro spray ionization (ESI+). Modified QuEChERS methods with 1 % ethyl acetate in acetonitrile involved in the extraction of profenofos residues from green pods and mature dry grains. Results: The limit of detection and limit of quantification (LOD and LOQ) were 0.002 and 0.006 µgg-1, respectively. The recovery ranges from 88.75 to 101.36 % for the green pods and 88.34 to 98.77 % for mature dry grains with relative standard deviation (RSD) was in the range of 0.99 to 4.05 %. The field study was conducted to investigate the dissipation kinetics of profenofos in pigeonpea. Two applications of profenofos 50 % EC at 500 and 1000 g a.i.ha-1 at 15 days intervals in pigeonpea at the time of pod formation recorded initial deposits of 20.28 and 41.64 ìgg-1 in the green pod, respectively. At15 days after application, residues gradually dissipated to the level of 0.78 and 1.98 µg g-1 accounting to the loss of 96.15 and 95.58 % at 500 and 1000 g a.i. ha-1, respectively. The half-life values were 5.18 and 5.93 days. Hazard index (HI) was found less than 1 at 25th and 35th day after application at 500 and 1000 g a. i. ha-1, respectively.