Resumen
It has been employed a mechanized procedure for the spectrophotometric determination of anionic surfactants in sea sand samples. The method is based on a batch leaching of surfactants from sand with two hot water successive treatments followed by on-line reaction of the extracted surfactants with methylene blue (MB) and extraction in chloroform using the multicommutation approach. The dynamic linear range was evaluated till 8.7 × 10–6 mol L–1 (2.48 mg L–1) sodium dodecyl sulphate (SDS). A solvent consumption of 0.7 mL per determination, a sampling throughput of 40 measurements per hour, a relative standard deviation of 4.2% (n=10) for a 2 × 10–6 mol L–1 (576 µg L–1) surfactant standard and a limit of detection of 1.4 × 10–7 mol L–1 (0.04 mg L–1) were the analytical parameters obtained for the on-line reaction. Quantitative recoveries, between 92.2 and 100.0%, were found for the determination of anionic surfactants in sand samples spiked with amounts of SDS from 0.75 to 3 µg g–1.