A sequential-injection system for spectrophotometric determination of p -aminobenzoic acid in sunscreens.

A sequential injection method is proposed for spectrophotometric determination of p-aminobenzoic acid (PABA) in cosmetic formulations. The method is based on diazotization of the analyte, coupling with 8-hydroxyquinoline, and the subsequent formation of a colored product. The experimental conditions used (coupling reagent, sandwich arrangement, volumes aspirated, propulsion flow rate, reaction coil length) were studied. Response of the sequential injection method were linearly dependent on concentrations up to 25 micro g mL(-1) and the detection limit was 2 micro g mL(-1). Throughput was 51 measurements per hour and a complete cycle, including three measurement per sample and a washing step…