Simultaneous (or sequential) determination of the total polyphenol index (or I280) and density in wines by flow injection

Abstract

Flow injection methods for the determination of the total polyphenol index, the ‘index 280’ (I₂₈₀) and dissolved solids in wines are proposed. The determination of the total polyphenol index is based on the Folin–Ciocalteu reaction in a basic medium and subsequent spectrophotometric detection at 750 nm. The direct measurement at 280 nm of the wine allows the determination of I₂₈₀ with a simple manifold. The dissolved solids determination is based on the displacement of a light beam when the refractive index of the medium changes. This phenomenon, followed by a change in the absorbance in a photometric detector, usually takes place when an injected sample reaches the flow cell, and it is magnified on passage of the light beam in the radial direction instead of the more common axial direction. The use of a capillary (4 cm × 1.1 mm id) as the flow cell allows monitoring of the injected plug. A simple manifold coupled with a diode array spectrophotometer allows the determination of these parameters with a frequency of at least 90 h⁻¹. Depending of the method adopted for the determination of polyphenols, Folin–Ciocalteu or I₂₈₀, either a manifold different from that used for determining dissolved solids or the same, respectively, is required. The methods have been successfully applied to different wines and were substantiated well with official methods.