Voltammetric and amperometric determination of n-nitroso antineoplastic drugs at mercury and amalgam electrodes

A hanging mercury drop electrode and a mercury meniscus modified silver solid amalgam electrode were used as electroanalytical sensors for voltammetric determination of antineoplastic drugs carmustine, lomustine and streptozotocin containing reducible N-nitroso groups. On the example of carmustine it was shown that its one-step reduction proceeds at substantially more negative potentials at amalgam electrode as compared with mercury electrode. Both electrodes offer satisfactory repeatability of current response (relative standard deviations < 5%) using DC voltammetry and differential pulse voltammetry. The achieved limits of determination lie mostly in the 10^-7 mol l^-1 concentration range. The mentioned voltammetric methods were applied to determination of carmustine and lomustine in pharmaceutical formulations. Further, the mercury meniscus modified silver solid amalgam electrode was employed in a "wall-jet" amperometric detection cell in the determination of carmustine by flow injection analysis. Under optimized conditions (run electrolyte Britton-Robinson buffer of pH 7.0; flow rate 5.5 ml min-1; detection potential-1.5 V; injection volume 0.02 ml) the limit of quantitation 7.1 × 10^-6 mol l^-1 was achieved.