Polarographic behaviour of loratadine and its direct determination in pharmaceutical formulation and human plasma by cathodic adsorptive stripping voltammetry.

The polarographic behaviour of the antihistaminic drug loratadine has been investigated in B.R. buffer solution of different pH values. Contradictory to that mentioned before in a previously published work, loratadine is electro-active at the mercury electrode. In B.R. buffer solution of pH values > or =6 it is reduced via a single 2-electrons irreversible wave corresponding to saturation of carbon-nitrogen double bond of the pyridine ring. The electrode reaction pathway was proposed and discussed. A sensitive differential pulse stripping voltammetric method based on controlled adsorptive accumulation of loratadine on a hanging mercury drop electrode has been developed for its direct determination at nanomolar concentrations without nitration of the drug. The optimized conditions for the direct cathodic adsorptive stripping voltammetric determination of the drug are: 0.1 M sodium hydroxide solution as a supporting electrolyte, accumulation potential, -1.2 V; accumulation time, 30 s; scan rate, 2-5 mV x s(-1) and pulse amplitude 100 mV. The proposed procedure was applied for the assay of loratadine in pharmaceutical formulation and human plasma. The average recoveries were 99.32-99.44 and 100.33-102.99% with the RSD 0.27-0.42 and 0.39-0.90% in pharmaceutical formulation and human plasma, respectively. The limits of detection of 1.60x10(-7) and 1.25x10(-7) M loratadine were found in pharmaceutical formulation and human plasma, respectively.