Cloud point extraction combined with micellar electrokinetic capillary chromatography determination of benzophenones...

A method has been developed for the separation and determination of three hydrophobic benzophenones: 2,4-dihydroxybenzophenone (BP-1), 2,2'4,4'-tetrahydroxybenzophenone (BP-2), and 2-hydroxy-4-methoxybenzophenone (BP-3) in sunscreen by micellar electrokinetic capillary chromatography (MEKC) combined with cloud point extraction (CPE). The analytes were extracted at pH 5.0 by micelles of the nonionic surfactant polyoxyethylene-7.5-octylphenyl ether (Triton X-114). A 150 microL aliquot from the extracted surfactant-rich phase was diluted up to 500 microL with ethanol to reduce its viscosity before separation by MEKC. A background electrolyte of 25 mmol/L sodium tetraborate containing 30 mmol/L sodium dodecyl sulfate at pH 9.25 was used as the separation medium to avoid the adsorption of hydrophobic substances and Triton X-114 onto the inner surface of the separation capillary, ensuring the separation efficiency and reproducibility. Detection is performed at 290 nm. Under the optimized conditions, an enrichment factor of 20 was obtained and the determination limits of BP-1, BP-2, and BP-3 were found to be 3.90 x 10(-) (7), 3.83 x 10(-7), and 6.42 x 10(-8) mol/L, respectively. In comparison with the earlier reported methods, the LODs of this method are superior to the other methods. The presented procedure was successfully applied to the determination of BP-1, BP-2, and BP-3 in sunscreen with satisfactory results.