Pervaporation-flow injection analysis of phenol after on-line derivatisation to phenyl acetate

A reverse pervaporation-flow injection (rPFI) method coupled with on-line derivatisation was developed for the determination of trace phenol in aqueous samples. On-line rPFI derivatisation was performed by direct injection of acetic anhydride into a donor stream of standard or sample phenol solution, which had been merged upstream with an alkaline concentrated sodium chloride stream. The reaction mixture was passed through a mixing chamber to generate phenyl acetate, which was then transported to the pervaporation unit. After evaporation into the headspace of the pervaporation unit, phenyl acetate diffused through a hydrophobic membrane into a static alkaline solution in the acceptor chamber where it was trapped for 15 min. Phenyl acetate was converted to phenolate ions and then transported to an electrochemical detector where it was analysed amperometrically at a glassy carbon electrode at +0.62 V (versus Ag/AgCl). The calibration plot was linear over the range of 50–1000 μg l −1 with a sample throughput of 4 h −1. The detection limit was determined to be 25 μg l −1 and 4.85% R.S.D. for n=6 (at 1000 μg l −1). This new method was applied to the analysis of several samples and the data compared with those obtained by the standard 4-aminoantipyrine (4-AAP) method and reversed-phase HPLC.