A SO2-selective electrode based on a Zn-porphyrin for wine analysis

• An innovative SO2-selective electrode based on coordinated complexes between amines and metalloporphyrins.
• Lower detection limits allow the evaluation of SO2 in different wine preparation steps.
• Can be applied to the analysis of the free and total SO2 in wine samples.
• Higher accuracy and precision when compared with a reference method.

This work describes the assessment of a SO2-selective electrode based on the use of the neutral carrier 5,10,15,20-tetraphenyl(porphyrinate)zinc(II) in a PVC membrane plasticized with 2-nitrophenyl phenyl ether. After being conditioned in 2 mol L−1 diethylamine solution for 24 h, the electrode exhibited selective anionic response toward the analyte in a concentration interval of more than four decades, with an slope of −59.5 mV dec−1, a practical detection limit of 3.7 × 10−6 mol L−1 and a low limit of linear range of 7.2 × 10−6 mol L−1. The response mechanism is based on the displacement of the diethylamine:metalloporphyrin complex equilibrium within membrane bulk, inducing a variation in the cationic-sites to ionophore ratio. In turn, free hydroxyl ions are complexed by the displaced ionophore in a ratio 1:1 and translated as single negative charge nernstian response. Finally, the selectivity of the electrode is evaluated in view of its application to wine analysis. Results had high accuracy and precision when compared with a reference method.

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