Selective carbonaceous-based (nano)composite sensors for electrochemical determination of paraquat in food samples

A novel electrochemical sensor based on activated biochar (AB4) and reduced graphene oxide (rGO) was developed and tested for detection of paraquat (PQ) in food samples. Precursor biochar was obtained by the pyrolysis of water hyacinth biomass at 400, 500, and 600 degrees C, followed by a chemical activation step using HNO3 to increase the amount of oxygenated and nitrogenated groups. The modified electrodes (rGO-AB4) were tested in different experimental conditions, and exhibited good response under the optimized conditions, showing linearity from 0.74 to 9.82 mu mol L -1 and a limit of detection and limit of quantification of 0.02 mu mol L-1 and 0.07 mu mol L-1, respectively. Interfering species such as glyphosate caused insignificant changes in the peak current of paraquat, and the selectivity of the method was tested using blank and spiked samples of coconut water, wastewater, honey, lettuce and lemon. Recovery ranged from 87.70 +/- 2.07% to 103.80 +/- 3.94%.