Voltammetric determination of nitronaphthalenes at a silver solid amalgam electrode

Electrodes based on amalgam materials were re-introduced in electroanalytical chemistry in the year 2000, partially as reaction to unsubstantiated public fears of liquid mercury. In this publication, the voltammetric behavior of 1-nitronaphthalene and 2-nitronaphthalene was investigated at a mercury meniscus-modified silver solid amalgam electrode. The reduction mechanism in mixed neutral buffer-methanol medium includes the four-electron reduction to hydroxylaminoderivative followed by a two-electron reduction to the amine in acidic medium, similarly to mercury electrodes. In alkaline media, both compounds show the splitting of the main four-electron reduction peak typical for mercury electrodes in two new ones, the first one corresponding to a one electron reduction of the nitroderivative to the nitro radical anion, which was confirmed by microcoulometry. Using optimized conditions (differential pulse voltammetry, Britton-Robinson buffer pH 7.0 - methanol (9:1) medium) the calibration dependences are linear in the range of 2 · 10^-7 (4 · 10^-7) to 1 · 10^-4 mol L^-1 for 1-nitronaphthalene (2-nitronaphthalene). After preconcentration of the analytes from drinking and river water samples using solid phase extraction the limit of determination was lowered to ∼3 · 10^-8 mol L^-1.