Development of a New Coated Graphite Electrode for Hydroxychloroquine Sulfate Determination in Pharmaceutical Preparations and Human Urine

A simple, rapid and sensitive method for the determination of hydroxychloroquine sulfate using coated graphite electrode (CGE) was developed. The membrane film of the electrode made of 5.0% (w/w) ion-pair of hydroxychloroquine sulfate (HCQS) with sodium tetraphenylborate (NaTPB) and 47.5% (w/w) of each of dibutyl phthalate (DBP) as plasticizing solvent and poly vinyl chloride (PVC). The electrode showed Nernstian slope of 30.0±0.2 mV decade-1 at 25±0.1°C within the concentration range of 7.1×10-5 to 1.0×10-2 mol L-1 (HCQS), with a detection limit of 1.8×10?5 mol L-1 HCQS and response time ? 10 s. Up to 24 h continuous soaking, the calibration graph slope was constant at 30.0±0.2 mV decade-1 at 25±0.1°C, then it decreased gradually as reaching 23.6±0.6 mV decade-1 after 20 days. The changes in pH did not affect the electrode performance within the range of 2-7. The standard electrode potentials were determined at different temperatures and used to calculate the thermal coefficient of the electrode. The electrode showed very good selectivity for HCQ cation with respect to a number of common inorganic and organic species. The standard addition method and potentiometric titration were used to determine HCQS in pure solutions, pharmaceutical formulations and human urine.