Determination of Polyphenol Content by Formation of Unstable Compound Using a Mini-Pump Multicommutation System

Abstract

This article describes a multicommuted flow procedure for photometric determination of the polyphenol content in wines and teas, exploiting the formation of unstable intermediate products, by the reaction of sodium hypochloride with gallic acid. Because the lifetime of the formed compound is very short, a special flow cell was designed in order to enable mixing of sample and reagent solution within the flow cell, thus allowing signal monitoring, while compound formation proceeded. The flow system manifold comprised three solenoid mini-pumps to propel sample, reagent solution, and carrier fluid. The photometer consisted of a photodiode and a light emitting diode (LED) with maximum emission at 490 nm. Under the selected operational conditions, useful features including a linear response ranging from 62 to 1000 mg L −1 gallic acid solution (R = 0.9987), a detection limit of 21 mg L −1 gallic acid, a sampling rate of 120 determinations per hour, a relative standard deviation of 1.9 % (n = 20) for a typical solution containing 400 mg L −1 gallic acid, and a waste generation of 1.0 mL per determination were also achieved. Medium recovery values of 96.2 ± 10.4 and 101.9 ± 7.3 % for wines and teas, respectively, were achieved.

Chemical Derivatization in Flow Analysis

“…Moreover, the ability to detect unstable yet reproductively formed species allows the proposals of novel analytical methods and represents a clear advantage of flow analysis. Examples of applications are presented in Table 2 [ 30 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 ]. Moreover, the instability of the measured species can be exploited to improve selectivity, as demonstrated in the ingenious determination of ascorbic acid relying on its intrinsic UV absorption [ 110 ].…”