Abstract: Two types of polyvinyl chloride (PVC) matrix membrane electrodes responsive to the antimalarial drug chloroquine have been constructed, electrochemically evaluated, compared and used in pharmaceutical analysis. Type 1 is the classic PVC model with chloroquine-tetraphenylborate (TPB) sensor; Type 2 is a coated silver disk without internal filling solution. Both electrode types exhibited rapid linear potentiometric response to the logarithmic concentration of diprotonated chloroquine cation in the 10^-1 - 10^-6 M range with calibration slopes 28-30 mV/concentration decade over the pH range 1.8-6.2. These electrodes were sensitive enough to permit determination of chloroquine phosphate at concentrations as low as 5µg/mL with good accuracy and precision. Determination of chloroquine in various pharmaceutical preparations using direct potentiometry and potentiometric titration with NaTPB gave an average recovery of 98.8% of the nominal values (SD 0.5%). The Type 2 electrode was also assessed in a flow-through sandwich cell for flow injection analysis. Results were compared with data obtained by the U.S. Pharmacopeia method. Two membrane electrodes are described, both incorporating a PVC membrane plasticized with dioctyl phthalate and containing the chloroquine (I) - tetraphenylborate ion-pair complex: a conventional membrane electrode with 5 mM chloroquine phosphate - 5 mM KCl as filling solution, and a membrane-coated Ag-disc all-solid-state electrode. Both electrodes gave rectilinear response from 1 µM to 0.1 M I at pH 1.8 to 6.2 with a slope of 28 to 30 mV per decade. The limit of determination was 5 µg mL-1, and accuracy and precision were good. The all-solid-state electrode was also assessed in a flow injection cell.

Abstract: A potentiometric polyvinyl chloride membrane comprising of bis(2-ethylhexyl)adipate as plasticizer and potassium tetrakis(4-chlorophenyl)borate was developed as a chloroquine sensor. The sensor was later applied as a detector in a flow injection analysis set up where it was not only successfully used in the determination of active ingredient in pharmaceutical preparations but also in establishing the dissolution profiles for chloroquine tablets. The flow through chloroquine sensor offers high accuracy and excellent repeatability, with large sample throughput (90 mL min-1). Besides being simple, the technique is rapid, low cost and allows direct quantification of chloroquine (without sample pretreatment).