Determinação voltamétrica de ácido salicílico em amostras de leite com um eletrodo de fio de cobre

Abstract

Salicylic acid (SA) is widely used in the dermatological and pharmaceutical industries due to its antiseptic, anti-inflammatory, and exfoliating properties; however, its use as a food additive is not permitted. Despite this prohibition, cases of milk adulteration with SA are frequently reported in several countries. Besides compromising the quality of milk and dairy products, this adulteration represents a serious health risk to consumers, demonstrating the relevance of efficient analytical methods for the quantification of SA in complex matrices such as milk. This work presents an environmentally friendly voltammetric method for the determination of SA in milk, using a working electrode made of commercial copper wires, subsequently subjected to a chemical modification in an alkaline medium to form a CuO-rich layer that protects against electrode fooling and improves the electrochemical response of SA. The technique employed was Differential pulse voltammetry, which, after parameter optimization, yielded a linear range of 10 to 500 µmol L⁻¹ and a detection limit of 3.0 µmol L⁻¹. Another highlight is the sample treatment using only ZnSO₄ and NaOH, the former precipitates milk proteins, while the latter ionizes the SA, facilitating its extraction and subsequent detection. This procedure reduces reagent and sample consumption, eliminates organic solvents, and allows for rapid pre-treatment of multiple samples simultaneously. In the spike-and-recovery study for fortified samples, the recovery percentages of AS ranged from 91 to 107%, with RSD values from 2.1 to 5.3%, results consistent with the AOAC guidelines for evaluating the performance of analytical methods. Therefore, this work offers a low-cost procedure, more sustainable than the established method for determining AS in food, and with satisfactory analytical performance, representing a promising strategy for the quantification of AS in milk samples.