Multiresidue Pesticide Analysis Using QuEChERS Method in Vegetable Samples by Ultra-Performance Liquid Chromatography

A Laser Reduced Graphene Oxide Grid Electrode for the Voltammetric Determination of Carbaryl

Laser-reduced graphene oxide (LRGO) on a polyethylene terephthalate (PET) substrate was prepared in one step to obtain the LRGO grid electrode for sensitive carbaryl determination. The grid form results in a grid distribution of different electrochemically active zones affecting the electroactive substance diffusion towards the electrode surface and increasing the electrochemical sensitivity for carbaryl determination. Carbaryl is electrochemically irreversibly oxidized at the secondary amine moiety of the molecule with the loss of one proton and one electron in the pH range from 5 to 7 by linear scan voltammetry (LSV) on the LRGO grid electrode with a scan rate of 300 mV/s. Some interference of the juice matrix molecules does not significantly affect the LSV oxidation current of carbaryl on the LRGO grid electrode after adsorptive accumulation without applied potential. The LRGO grid electrode can be used for LSV determination of carbaryl in fruit juices in the concentration range from 0.25 to 128 mg/L with LOD of 0.1 mg/L. The fabrication of the LRGO grid electrode opens up possibilities for further inexpensive monitoring of carbaryl in other fruit juices and fruits.

LC-MS/MS method optimization and validation for trace-level analysis of 71 crop protection chemicals in pulses

An analytical method involving modified QuEChERS (quick, easy, cheap, effective, rugged and safe) technique coupled with LC-MS/MS (liquid chromatography-tandem mass spectroscopy) has been developed for simultaneous identification and quantification of 71 pesticides (insecticides/acaricides/nematicides (32), fungicides (12), herbicides (26), plant growth regulator (1)) in different pulses (edible seeds of leguminous plants), namely gram, lentil, black gram and pea. The analysis was done using Shimadzu LC-MS/MS-8030 instrument equipped with Zorbax Eclipse Plus C-18 column operating under electrospray ionization (ESI) in positive and negative modes. Validation of method was done as per a single laboratory validation approach. Nine-point linear calibration curves for each pesticide were obtained in the range of 0.005 to 2 μg/g with correlation coefficient of ≥ 0.98. Limit of detection (LOD) for all the pesticides was achieved in the range of 0.001-0.015 μg/g, whereas the limit of quantification (LOQ) were found in the range of 0.01-0.05 μg/g. Recovery studies were conducted at 0.01- and 0.05-μg/g level of fortification using modified buffered QuEChERS method standardized for low moisture foods. It was observed that due to matrix interference, only around 75% of the pesticides were recovered in an acceptable range of 70-120% when compared against the solvent standard. With matrix-matched standards, 95% of the recovery results came within acceptable range with highly acceptable HorRat ratio (between 0.2 and 0.8) indicating satisfactory precision. The global and expanded uncertainties for estimation of each pesticide in above-mentioned pulse matrices were calculated to evaluate the suitability of the developed method for quantification of pesticides in pulse matrices.