Preconcentration of lead complexed with O,O-diethyl-dithiophosphate by column solid-phase extraction using different sorbents in a flow injection system coupled to a flame atomic absorption spectrometer

A comparative study of C18 immobilized on silica, activated carbon and a polyurethane foam, as sorbents for Pb complexed with O,O-diethyl-dithiophosphate in a flow injection preconcentration system is reported. The complex was formed in 1.0 M HCl medium and processed in a simple system using a peristaltic pump, a manual injector–commutator and a mini-column filled with the sorbent. Using ethanol as eluent, the richest 150-μl fraction was collected and measured (after discarding 150, 200 and 0 μl for the activated carbon, foam and C18, respectively) by flame atomic absorption spectrometry. The optimum concentration of the complexing agent was 0.05% m/v for C18 and 0.2% m/v for the activated carbon and the polyurethane foam. The best sample loading flow rate was 4.0 ml min−1 for the activated carbon and 2.0 ml min−1 for C18 and the polyurethane foam, while the best elution flow rate was 1.0 ml min−1 (activated carbon) and 0.6 ml min−1 (C18 and foam). It was found that beyond a certain loading sample volume, for a constant analyte mass, the signal decreased. The maximum loading sample volume, for a constant analyte mass, before the signal started to decrease, was 50 ml for the activated carbon and 150 ml for the other materials. By processing 25 ml, the enrichment factors were 23, 55 and 166 for the activated carbon, foam and C18, respectively. The best limit of detection (3σ) was 0.3 μg l−1 for the C18 (1.2 μg l−1 for the foam and 3 μg l−1 for the activated carbon). As shown, the C18 has a much superior retention performance in comparison to the other two materials.