Flow Injection Spectrophotometric Determination of Total Polyphenols in Black Tea Processed and Marketed in Ethiopian

Abstract

The present study proposes an alternative flow injection spectrophotometric method for the quantification of total polyphenols in tea samples. The method was based on the reaction between polyphenols and 4-aminoantipyrine (4-AAP) in the presence of hexacyanoferrate in alkaline medium. A reddish-brown coloured product is formed as a result of a reaction between polyphenols and 4-AAP in the presence of oxidizing reagent, hexacyanoferrate, in alkaline medium which was detected at a wavelength of 520 nm. Standard gallic acid solutions prepared in the range of 10- 500 mg/L was used to plot a calibration graph. A good linear calibration graph (r= 0.997, n= 5) was obtained by plotting A (520nm) values versus gallic acid standards solutions (10- 500mg/L). The effect of several experimental conditions such as the effect of pH, reaction coil length, flowrate, the concentration of 4-AAP and concentration of hexacyanoferrate (HCF) were optimized and applied to flow injection analytical system. The proposed method was applied for the quantification of total polyphenol in selected tea samples and the result obtained are given as gallic acid equivalent (GAE) mg/L with RSD < 5.

Keywords: Flow Injection, Amino-Antipyrine, Total-Polyphenol