FI-Online Enzymatic Oxidation and Preconcentration by PVA Modified Membranous Capillary-Photometric Determination of Total Phenols in Water

Polyphenol oxidase (PPO) was immobilized on the surface of PTFE membranous capillary by using adipoyldichloride as crosslinking agent.A FI-manifold was used for the on-line analytical process.Phenols in water sample were enzymatically oxidized when cycling in the PVA-PPO modified PTFE membranous capillary,and the oxidation products of phenols were reacted with 4-aminoantipyrine to give a colored compound.The colored solution of definite volume was enriched by cycling for 15 min in the un-modified PTFE membranous capillary,the colored compound was eluted from the unmodified capillary with ethanol,and the absorbance of the eluate was measured at the wavelength of 510 nm.Optimum parameters of time for on-line enzymatic oxidation,time for on-line color reaction,flow-rate of introduction of sample solution in reaction cycle 1 and 2,and flow-rate of the eluant during elution,were given and the reaction was carried out in PBS of pH 6.8.Range of linearity found was between 0.5-60 μg·L-1.Common co-existing ions and compounds were found to be non-interfering.The proposed method was used in the analysis of samples of ground water and tap water,the results were checked by the international standard method,giving relative errors ranged from 1.8% to 3.3%.