Determination of paraquat residues in lettuce and cabbage grown in Lepaterique by HPLC-DAD

Abstract

Determination of residues of the herbicide paraquat in lettuce (Lactuca sativa) and cabbage (Brassica oleracea) produced in the community of La Brea, Lepaterique and marketed in the city of Tegucigalpa was carried out in October and November of 2017, through the application of high performance liquid chromatography with detector of diode array (HPLC-DAD) in less than 6 minutes, with a reverse phase separation mechanism using a C18 surface porous column and a mixture of 0.1 M orthophosphoric acid (pH 3.0) with acetonitrile in proportion of 3:1 as mobile phase. The method is based on extraction with an ultrasonic bath using water as an extractive solvent and the subsequent application of solid phase extraction (SPE) with weak ion exchange (WCX) sorbent. The different parameters of the extraction (extractor solvent, sonication time, cleaning solvent and elution solvent) were evaluated to optimize the efficiency
of the extraction process. Validation of the method was carried out by fortifying samples at 0.05 and 1mg Kg-1, with three replicates (n = 3) for each concentration, determining linearity, accuracy (expressed as percent recovery), detection limits (LOD) and quantification (LOQ). The limit of detection of the method was 0.025 mg Kg-1, which is below the maximum residue limit (MRL) established by the Codex Alimentarius (0.07 mg Kg-1) for leafy vegetables. The acquired samples were analyzed following the validated method, without finding paraquat residues in a total of 10 samples of each vegetable.