ON LINE COUPLING OF A LIQUID-LIQUID-EXTRACTION FLOW-REVERSAL SYSTEM TO A SPECTROPHOTOMETRIC FLOW-THROUGH SENSOR FOR THE DETERMINATION OF POLYPHENOLS IN OLIVE OIL

The coupling of a liquid-liquid extraction approach based on flow-reve rsal to a flow-through sensor is proposed. The basis of the sensor is the use of Folin-Ciocalteau reagent immobilized on an anionic exchange resin packed in a flow cell located in a spectrophotometer, where the reaction product (molybdenum blue) is formed, retained and detected o n the resin surface, thus integrating the reaction, retention and dete ction. The regeneration of the sensor is accomplished by passing an ac idic Ce(IV) solution through it. This coupled system allows the extrac ted analytes (polyphenols) to be monitored continuously, and it was us ed to develop a method for the determination of polyphenols in oil. Th e proposed method features two linear response ranges, from 15 to 30 a nd from 30 to 90 mu g ml(-1), expressed as caffeic acid, with a relati ve standard deviation < 3.1%. The 3 sigma detection limit was 10 mu g ml(-1) caffeic acid. It was applied to the determination of polyphenol s in olive oil samples with results in excellent agreement with those provided by a conventional method.