Multivariate Optimization of an Analytical Method for Bisulfite Determination in Vinegar Samples Using Digital Images

This work proposes an analytical method based on digital images to indirectly determine bisulfite in vinegar samples using the colorimetric reaction between Fe(II) and the complexing agent 2,2′-bipyridine. Optimization was conducted using a multivariate methodology. Firstly, a two-level full factorial design was performed to identify the factors with significant effects on the analytical response through a two-level full factorial design (2³). The studied variables included pH, 2,2′-bipyridine concentration, and sample volume. Subsequently, a Doehlert matrix was employed to establish the optimal conditions for the significant variables. The recommended procedure involved a reaction pH of 5.7 and a 0.0038 mol L⁻¹ 2,2′-bipyridine concentration, with a sample volume of 0.75 mL. The proposed method exhibited a linear response within the range of 0.45 to 300 mg L⁻¹ of bisulfite, with detection and quantification limits of 0.15 mg L⁻¹ and 0.45 mg L⁻¹, respectively. The method’s precision, assessed through relative standard deviation, was 3.4% (n = 10, 1.0 mg L⁻¹). Accuracy was evaluated through recovery tests, with results ranging from 97 to 114%. Furthermore, a comparison was made between the bisulfite concentrations determined using the proposed method and those obtained through a reference method based on iodometric titration. The method was successfully applied to determine bisulfite in commercial vinegar samples. The bisulfite concentration varied from (14 ± 1) mg L⁻¹ to (261 ± 3) mg L⁻¹.