Adsorptive differential-pulse stripping voltammetry of norfloxacin and its analytical application

Abstract

Cyclic voltammetric investigations have been performed which showed that norfloxacin exhibits adsorptive processes at the hanging mercury drop electrode (HMDE) in various base electrolytes of pH < 9 such as LiCl, NaCl—NaOH (pH 8.8), CH₃CO₂Na, CH₃CO₂Na—CH₃CO₂H (pH 7.5) and NH₃—NH₄Cl (pH 8). Adsorptive preconcentration followed by differential-pulse cathodic stripping in various base electrolytes showed voltammograms of three waves in the ranges of –1.02 to –1.18, –1.28 to –1.34 and –1.43 to –1.54 V with the one at –1.02 V being the most sensitive wave in most cases. The optimum experimental parameters were assessed for each base electrolyte. In general, accumulation potential, E_acc, scan rate, v, and accumulation time, t_acc, were found to be in the ranges of 0 to 0.1 V, 2 to 10 mV s^–1 and 60 to 300 s, respectively.

The calibration plots showed more than one linear segment in the same base electrolyte. These segments covered ultratrace levels of norfloxacin extended from 0.32 to 900 ng l^–1(1.0 × 10^–12 to 3.0 × 10^–9 mol l^–1) and from 0.32 to 65 µg l^–1(1.0 × 10^–9 to 2.0 × 10^–7 mol l^–1) depending on the base electrolyte and the adsorptive peak used for analysis. These linearities may be ascribed to pure adsorptive and mixed adsorptive–diffusion processes. Ten successive adsorptive stripping peak measurements yielded relative standard deviations, s_r, of 2.5 to 6.0% for various norfloxacin concentrations in the range of 4.82 to 39.6 µg l^–1 in different base electrolytes. Norfloxacin in Noroxin commercial tablets was determined using the standard addition technique for concentrations at ng l^–1 and µg l^–1 levels. Good recoveries were obtained without an interference of the drug excipients.