Flow injection spectrophotometric determination of total phenols using a crude extract of sweet potato root (Ipomoea batatas (L.) Lam.) as enzymatic source Original Research Article

A flow injection spectrophotometric method is proposed for the determination of total phenols in industrial wastewaters. After selection of the extraction medium (e.g., buffer-to-tissue ratio, pH, buffer concentration, protective agents and/or stabilizers) and storage conditions, crude extract of sweet potato root (Ipomoea batatas (L.) Lam.) was used as an enzymatic source of polyphenol oxidase (PPO; EC 1.14.18.1) directly in the carrier. This enzyme catalyses the oxidation of mono-, di-, and polyhydric phenols to o-quinones which can couple to each other producing melanin-like pigments with a strong absorption at 410 nm. For the optimum extraction conditions, the enzyme activity did not vary for at least five months when stored at 4°C and decreased only 4–5% during an 8 h working period at 25°C. The results obtained for the determination of total phenols in industrial wastewaters are in good agreement with results obtained using a conventional manual method (correlation coefficient, r=0.9954). Twenty-six results were obtained per hour, and the relative standard deviation (r.s.d.) was less than 2.7% (n=6) for all samples. The detection limit (three times the signal blank/slope) was 1.0×10−5 mol l−1 and the recovery of catechol from three samples ranged from 96.4 to 102.7% of added amount.