Sensitive sequential-injection system for the determination of 2-phenylbenzimidazole-5-sulphonic acid in human urine samples using on-line solid-phase extraction coupled with fluorimetric detection.

2-Phenylbenzimidazole-5-sulphonic acid (PBS) is an UV-filter contained in many cosmetics as a sunscreen. A direct, selective and sensitive method to determine traces of PBS is presented. The on-line separation of this compound from urine matrix was directly coupled with fluorimetric detection in a sequential-injection system. The separation was performed using a SAX microcolumn in which the analyte was retained and eluted selectively. The determination is carried out without any derivatization reaction, by directly measuring the intrinsic fluorescence of the analyte. The wavelengths of excitation and emission were 301 and 681 nm, respectively. On-line standard addition calibration is performed into the system, and only one standard solution is required. The limit of detection was 12 ng ml(-1). The method was satisfactorily used to determine PBS in both, spiked and unspiked human urine samples, without any pretreatment. The relative standard deviations of the results were in the order of 2-13%. The concentrations of the analyte obtained for unspiked samples taken from sunscreen users were higher than the limit of detection.