FLOW-INJECTION SPECTROPHOTOMETRIC DETERMINATION OF TOTAL PHENOLS USING A CRUDE EXTRACT OF SWEET-POTATO ROOT (IPOMOEA-BATATAS (L.) LAM.) AS ENZYMATIC SOURCE

A flow injection spectrophotometric method is proposed for the determi nation of total phenols in industrial wastewaters. After selection of the extraction medium (e.g., buffer-to-tissue ratio, pH, buffer concen tration, protective agents and/or stabilizers) and storage conditions, crude extract of sweet potato root (Ipomoea batatas (L.) Lam.) was us ed as an enzymatic source of polyphenol oxidase (PPO; EC 1.14.18.1) di rectly 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. F or the optimum extraction conditions, the enzyme activity did not vary for at least five months when stored at 4 degrees C and decreased onl y 4-5% during an 8 h working period at 25 degrees C, The results obtai ned for the determination of total phenols in industrial wastewaters a re in good agreement with results obtained using a conventional manual method (correlation coefficient, r=0.9954). Twenty-six results were o btained per hour, and the relative standard deviation (r.s.d.) was les s than 2.7% (n=6) for all samples. The detection limit (three times th e signal blank/slope) was 1.0x10(-5) mol l(-1) and the recovery of cat echol from three samples ranged from 96.4 to 102.7% of added amount. ( C) 1998 Elsevier Science B.V.