Voltammetric behavior and quantification of the sedative-hypnotic drug chlordiazepoxide in bulk form, pharmaceutical formulation and human serum at a mercury electrode

Abstract

Chlordiazepoxide is a sedative-hypnotic drug widely employed as a transquilizer and anti-depressant. Its electrochemical behavior in Britton–Robinson (B–R) buffers of pH 2–11 at a mercury electrode has been investigated using dc-polarography, cyclic voltammetry and controlled-potential coulometry. Polarograms of the drug in B–R buffers of pH 2–10 exhibited three 2-electron waves, while at pH>10, only a single 4-electron wave was observed. The first, second, and third waves in buffers of pH≤10 may be attributed to the reduction of N-oxide, CN and CN centers, respectively. The single wave (pH>10) may be due to the reduction of both the N-oxide and CN centers in a one step. The shift of the E 1/2, values to more negative potentials upon the increase of pH indicated the involvement of protons in the electrode reaction and that the proton-transfer reaction precedes the electrode process proper. The estimated data indicated that, one proton and two electrons are participated in the rate-determining step of each of the reduced centers. The general sequence of chlordiazepoxide reduction processes via each of its reactant centers may be expressed as: H +, e, e, H + (fast). Based on the interfacial adsorptive character of the drug onto the mercury electrode, a validated direct square-wave adsorptive cathodic stripping (SWAdCS) voltammetric procedure has been described for the trace determination of the drug in bulk form, tablets and human serum. The procedure did not require sample pretreatment or time-consuming extraction or evaporation steps prior to the assay of the drug. The optimized operational conditions of the proposed procedure have been found to be: accumulation potential E acc.=−0.9 V, accumulation time t acc.=30 s, pulse-amplitude=50 mV, scan increment=10 mV and frequency=120 Hz. The proposed procedure is much more simple, fast, sensitive, costly low and achieved much more lower limits of detection (LOD) (4.4×10 −10 M and 6.6×10 −10 M) and limits of quantitation (LOQ) (1.5×10 −9 M and 2.2×10 −9 M), respectively in pharmaceutical formulation and spiked human serum, compared to previously reported methods.