Flow-through fluorescence-based optosensor with on-line solid-phase separation for the simultaneous determination of a ternary pesticide mixture

A rapid and selective method was developed for the simultaneous determination of 3 widely used pesticides, carbendazim (CBZ), carbofuran (CF), and benomyl (BNM). The method utilized a single continuous-flow, solid surface fluorometric multioptosensor implemented with a previous separation of the analytes on a minicolumn, placed just before the sensor, that was packed with the same solid support (C18 silica gel) as the flow-through cell. The separation was achieved because of the different kinetics of retention/elution of the pesticides on the solid support in the minicolumn, enabling the sequential arrival of the analytes at the sensing zone. With a single injection of the mixture, 2 of them were more strongly retained in the minicolumn (CF and BNM) while the other (CBZ) passed through the system towards the sensing material where it developed its fluorescence transitory signal. Then, CF and BNM were successively eluted from the solid support using 2 different eluting solutions, and they sequentially reached the sensing zone and developed their respective signals. A multiwavelength fluorescence detection mode was used, recording the signals of each pesticide at its maximum excitation/emission wavelength; therefore, the sensitivity was increased. The system was calibrated using a sample volume of 2000 microL. The linear dynamic range was 80-1400, 250-2400, and 150-2000 ng/mL with detection limits of 15, 68, and 35 ng/mL and relative standard deviation values of 3.5, 3.2, and 2.4% for CBZ, CF, and BNM, respectively. A recovery study was applied to spiked environmental water samples, and recoveries ranged from 96 to 104%.