A flow injection (FI) biosensor system for pentachlorophenol (PCP) using a substance recycling scheme

A flow injection (FI) biosensor system has been designed for the analysis of pentachlorophenol (PCP) using a substrate recycling scheme comprising immobilized bilirubin oxidase (BOX) in the presence of excess of NADH. PCP was efficiently converted to tetrachloro-p-benzoquinone (1,4-TCBQ) and then tetrachloro-p-hydroquinone (1,4-TCHQ) by bis(trifluoroacetoxy)iodobenzene (BTFAIB) and zinc powder, respectively. BOX immobilized on aminopropyl glass beads rapidly oxidized 1,4-TCHQ to 1,4-TCBQ, which in turn was readily reduced back to 1,4-TCHQ in the presence of excess NADH. This recycling scheme enabled one molecule of PCP to consume several NADH molecules leading to enhanced sensitivity. Under optimized conditions the rate of NADH uptake measured as the absorbance decrease at 340 nm yielded a detection limit for 1,4-TCHQ or oxidized PCP of 250 nM. The detection limit was improved to 25 nM for both analytes using a fluorescence detector with excitation and emission wavelengths of 345 and 450 nm, respectively. The PCP level in contaminated soil samples was measured using the FI biosensor system, and the results obtained compared well with capillary zone electrophoresis (CZE) analysis.