Flow-injection determination of polyphenols using a plant juice carrier

Abstract Banana pulp and spinach leaves exhibit enzyme acitivities of polyphenol oxidase and catechol oxidase (dimerizing), respectively, and the extracted solutions of these plants were employed as carriers for the determination of polyphenols. Spinach leaf juice was found to be superior to banana juice in terms of its long stability and broad linear rang of the calibration graphs for dopamine (1 × 10 −4 –6 × 10 −3 M), catechol (2 × 10 −4 –8 × 10 −3 M) and dl -epinephrine (2 × 10 −4 –6 × 10 −3 M). Each peak current returned to the original baseline completely within about 5 min when the flow-rate was 0.65 ml min −1 . The enzume activity of spinach leaf solution containing 0.3% of sodium azide did not vary for at least 7 days and it was found that this solution was useful as a carrier in a flow-injection system for the determination of polyphenols.