Sodium dodecyl sulphate-coated alumina for the extraction/preconcentration of benzimidazolic fungicides from natural waters prior to their quantification by liquid chromatography/fluorimetry

Sodium dodecyl sulphate (SDS)-coated alumina was used for the extraction/preconcentration of benzimidazolic pesticides (BFs) [carbendazim (CB), thiabendazole (TB) and fuberidazole (FB)] from river and underground water. SDS admicelles were required to get quantitative retention of BFs. Adsolubilization of analytes occurred through hydrophobic and electrostatic interactions. Methanol (1 ml) provided quantitative elution of the target analytes for all the samples analyzed. The high breakthrough volumes obtained (400 ml for CB and 1 l for BF and FB) and the low eluent volume used resulted in very high preconcentration factors (between 400 and 1000). Calcium was found to decrease BFs retention due to the disruption of SDS admicelles; however, this interference was easily removed by precipitation with SDS prior to BFs adsolubilization. The accuracy of the proposed method was assessed by studying recoveries of BFs in natural waters at two spiking concentration levels (80, 40 and 4 ng l−1, and 400, 200 and 20 ng l−1 for CB, TB and FB, respectively); mean recoveries in the intervals 96–105% and 98–108% were obtained for river and underground water samples, respectively.