Desenvolvimento de metodologia eletroanalítica para determinação de níquel em alimentos

Abstract

Nickel is one of the metals presents in stainless steel alloys used in the manufacture of food packaging and can therefore contaminate food by promoting consumer contamination. For this reason, it is important to develop analytical methodologies for the identification and quantification of nickel in industrialized foods. Unlike traditional techniques, electroanalytical techniques are faster, low cost and have low detection limits. Thus, the objective of this work was the development of an electroanalytical methodology for determination of nickel in industrialized foods using a silver solid amalgam electrode (AgSAE) together with the square wave voltammetry (SWV) technique with adsorptive redissolution steps. Initially, the analytical responses were evaluated in 0.1 mol L-1 of ammonium buffer solution at different pH values (pH 8.00 to 10.00). The influence of the application of potentials (Eacc) and times for adsorptive preconcentration (tacc) of Ni+2 over the AgSAE were also evaluated, followed by potential sweep in the range of 0.00 to -1.70 V. The value of Eacc was evaluated at potential values before, in the medium, at the top, in the medium (after the top) and at the end of the voltammetric peak during tacc from 0 to 90 seconds. The SWV parameters were also evaluated considering the height, position and width of the peak of reduction, where the frequency of application of the potential pulses (f) was evaluated from 10 to 300 s-1, the amplitude of pulses (a) of -5 to -50 mV and the scanning increment of potentials (ΔEs) from -2 to -10 mV. The addition of dimethylglyoxime complexing agent (DMG) was also evaluated, with an intense improvement in sensitivity and selectivity, characterized by the cumulative adsorption of nickel dimethylglyoxime on the surface of the AgSAE, followed by potential cathodic scans. Thus, the optimized experimental and voltammetric parameters were: 0.10 mol L-1 ammonium buffer pH 9.00, 90 μmol L-1 of DMG, Eacc of -0.857 V per tacc 30 seconds, f = 100 s -1, ΔEs = -2 mV and a = -25 mV. The analytical parameters (precision, accuracy, linear dynamic range, detection limits, quantification limits and recovery efficiency) were evaluated in pure electrolyte, and the results obtained are comparable to those obtained using conventional techniques such as mass spectrometry with plasma coupled inductively. Finally, the proposed methodology was applied to samples of natural water and coconut water, which were not previously treated by acid digestion. Solid samples of maize and tomato extract, purchased locally, were artificially contaminated with a known concentration of Ni+2 and were then digested with a mixture of concentrated acid (HNO3) and hydrogen peroxide (H2O2). Recovery curves were constructed in all samples, where it was observed that successive addition of aliquots of Ni+ 2 standard solution provided a linear increase in the peak current responses, allowing the calculation of the recovery efficiencies, which indicated that the results were satisfactory in terms of sensitivity, selectivity, repeatability and reproducibility.