Flow Injection Analysis System for the Determination of Total Phenolic Compounds by Using Folin-Ciocalteu Assay

Abstract

A simple, rapid and reliable flow injection analysis system for the determination of total phenolic compounds using the Folin-Ciocalteu method was established. The detection method was based on the reduction of a mixture of phosphotungstic and phosphomolybdic acid (Folin-Ciocaltue reagent) to tungsten and molybdenum oxide by phenolic compounds in the basic media and subsequent formation of a blue color product. The standard or sample solutions were injected into a carrier stream (distilled water) to react with a folin ciocaltue reagent and sodium carbonate to give the blue color product which was detected by spectrophotometer at 765 nm. The experimental conditions such as sample volume, flow rate of carrier and reagents, length of reaction coils and concentration of reagents were optimized. The relative standard derivation, RSD (20 replicates) of 5 ppm gallic acid was 0.72% with the detection limit (3S/N) of 0.0231 mg L-1. A good linear calibration curve in the range of 0.5-100.0 mg L-1 was obtained with regression equation y = 0.0123x + 0.021, R2 = 0.9991. The sampling throughput was 32 samples per hour. The effect of potential interferences such as citric acid, fructose and others were examined. The proposed method was successfully applied for the determination of the total phenolic compounds in tea.