Cost-Effective Voltammetric Determination of Salicylic Acid in Milk Using Copper Wire Electrodes

The illegal use of salicylic acid (SA) as a milk preservative raises significant health concerns, highlighting the need for accurate analytical methods capable of detecting this adulteration. This study presents an innovative, ecofriendly voltammetric method for SA determination in milk. The proposed method employs a working electrode fabricated from inexpensive, commercially available Cu wires, which were chemically modified with a CuO-rich layer grown electrochemically via cyclic voltammetry in alkaline medium (0.1 mol L^-1 NaOH). This modifying layer not only enhanced the voltammetric response of SA but also conferred antifouling properties to the working electrode. Differential pulse voltammetry, under optimized conditions, yielded a linear range of 10-500 μmol L^-1 with a limit of detection of 3.0 μmol L^-1. A key innovation is a simple and rapid sample pretreatment using aqueous solutions of ZnSO₄ and NaOH. The ZnSO₄ precipitates proteins, while NaOH ionizes SA, facilitating its extraction into the aqueous phase. This procedure minimizes sample and reagent consumption, eliminates organic solvents, and allows the processing of up to eight samples in 15 min. This environmentally friendly pretreatment, combined with the Cu/CuO electrode, enabled reliable SA quantification in spiked milk samples, with recovery percentages ranging from 91% to 107%. This approach offers a cost-effective, sensitive, selective, and more sustainable method for SA quantification in milk.