Determination of copper labile species in wine using diffusive gradients in thin-films technique with open and restricted diffusive gels

Copper labile species are involved in oxidation reactions in wine, thus affecting its quality and long-term stability. Consequently, the development of analytical methods capable of assessing the Cu labile fraction in wine is highly important. In this work, we developed an analytical methodology based on the use of the Diffusive Gradient in Thin-films (DGT) technique as passive sampling tool for DGT-labile species, followed by Cu determination using graphite furnace atomic absorption spectrometry (GF-AAS). DGT devices with Chelex resin gel and two types of diffusive gels, open pore (OP) and restricted pore (RP), were used in the experiments. The effective diffusion coefficients of Cu, determined in 12 % ethanol in water solution at 22 °C and pH 3.0, were (5.15 ± 0.28) × 10 −6 cm 2 s −1 for the OP gel and (4.47 ± 0.26) × 10 −6 cm 2 s −1 for the RP gel. Linearity assays for DGT in wine were evaluated over a 48-h deployment period, yielding determination coefficients of 0.9932 and 0.9867 for OP and RP, respectively. No significant differences were found for the Cu DGT-labile concentrations sampled using tools with OP or RP gels. The DGT-labile fraction of Cu in the seven analysed wine samples ranged from 7.0 to 33.1 μg L −1 , representing approximately 6.6 to 11.2 % of the total Cu concentration in the wine. By measuring Cu-labile species, producers in the winery sector can better control the Cu content in wine. • DGT passive sampling was applied to determine the labile fraction of Cu in wine. • Low pH typical to wine does not affect DGT analytical performance for Cu accumulation. • No difference was observed in the Cu DGT-labile concentration measured using OP and RP gels. • The effective diffusion coefficients of Cu in 12 % ethanol solution were determined. • The DGT-labile fraction of Cu ranged from 6.6 % to 11.2 % of the total Cu concentration.