Thesis (M.Sc.)--Chulalongkorn University, 2011

In this study, a new technique was developed using rapid ultra-performance liquid chromatography (UPLC)-based separation coupled with electrochemical detection by a boron-doped diamond (BDD) electrode for the detection and quantification of three commonly used parabens (methylparaben (MP), ethylparaben (EP) and propylparaben (PP)). The ultimate goal is aimed to reduce the analysis time by using UPLC coupled with a short reverse phase C18 monolithic column (25 mm x 4.6 mm). Operating the monolithic column at low back-pressure resulted in high flow rates. A mobile phase consisting of a 25:75 (v/v) ratio of acetonitrile: 0.05 M phosphate buffer (pH 5) at a flow rate of 2.5 mL min-1 was used to perform the separation. The amperometric detection with the BDD electrode was found to be optimal and reliably reproducible at a detection potential of 1.5 V vs. Ag/AgCl. Under these conditions, the separation of the three target analytes (MP, EP and PP) was achieved in 2 min and was linear within a sample concentration range of 0.1 to 50.0 mg L-1 (r2 > 0.997). This method was successfully applied to determine the concentrations of each paraben in six real samples with the recoveries ranging from of 80.3 - 98.9% for all three parabens from samples spiked at 12, 22 and 32 mg L-1. Therefore, the proposed method can be used as an alternative rapid and selective method for the determination of paraben levels in real samples.