Effect of KNO3 to remove silver interferences in the determination of mercury(II): Application in milk and breast milk samples

Mercury determination was performed at rotating silver electrode (RSE) using square wave voltammetry (SWV) in electrolytic mixture of HCl (0.1 mol L−1) and KNO3 (0.2 mol L−1). The reproducibility, sensitivity and accuracy are good, provided the proper instrumental parameters and supporting electrolyte are used. The relationship between the peak current of mercury(II) and its concentration is linear with regression equation: I(μA) = 0.784 [Hg(II)] + 49.5 (r2 = 0.9878) in the dynamic range from 1.0 × 10−7 to 8.0 × 10−4 mol L−1. The detection limit (DL,3σ) and quantification limit (QL,10σ) were 4.61 × 10−8 mol L−1 and 15.3 × 10−8 mol L−1, respectively. The relative standard deviation (RSD) for seven replicate analysis of a solution containing 5.0 × 10−5 mol L−1 was 2.19%. Possible effects of Cu, Co, Fe, MnO4, Zn, were investigated but did not cause any significant interferences. Immobilization of mercury(II) on the surface of rotating silver electrode obeyed to the Langmuir adsorption isotherm. The calculated ΔG°ads value showed that the interaction between mercury and silver electrodes is mainly controlled by a chemisorption process. This methodology was potentially applied for mercury determination in milk and breast milk samples.