Correction of predicted concentration in the use of solvent-based calibration lines for determining carbendazim, fuberidazole and thiabendazole in water after a SPE step

This paper addresses an attempt to overcome the deviation that results from the use of a solid phase extraction (SPE) procedure for extracting trace levels of three benzimidazole pesticides (carbendazim, fuberidazole and thiabendazole) from water samples, for their subsequent quantitative determination by spectrofluorimetry, using univariate calibration. The deviation is due to an attenuation effect originating in the C18 cartridge used in the SPE step. The approach developed is based on the calculation of a correction factor (fc) that is dependent on the signal measured after the SPE step. In order to calculate fc a study of the intermediate precision of two calibration graphs (with and without SPE) was performed. The fc was added to the predicted concentrations for the analytes using a calibration graph for pure solvent, built every time that the analysis is done. In addition, predictions were made using both average calibration graphs obtained from the intermediate precision study. In this study, the first of these three options was shown to improve the accuracy of predictions in the presence of matrix effects.