A comparative study of solid and liquid inner contact benzalkonium chloride ion-selective electrode membranes

A comparative study was made between two designs of benzalkonium ion (Bz)-selective electrodes: a silver-coated (solid contact) called electrode A and a PVC membrane (liquid inner contact) called electrode B based on benzalkonium-phosphomolybdate (Bz-PM) as ion-exchanger complex. Electrode A has a linear dynamic range from 2.0×10−8 to 1.0×10−2 mol L−1, with a Nernstian slope of 60±0.3 mV/decade and a detection limit of 2.0×10−8 mol L−1. Electrode B shows linearity over the concentration range from 2.0×10−7 to 1.0×10−2 mol L−1, with a Nernstian slope of 55±1.2 mV/decade and a limit of detection of 1.5×10−7 mol L−1. Electrode A showed better performance than electrode B. The detection limit of benzalkonium chloride (BzCl) was effectively improved by a solid contact ion-selective electrode (SC-ISE), rather than the traditional liquid inner contact electrode that gives lower detection limits because of diminished ion fluxes. The present electrodes show clear discrimination of BzCl from several inorganic, organic ions, sugars and some common drug excipients. The sensors were applied efficiently for determination of BzCl in its pharmaceutical preparations (eye, ear and nasal drops) using standard addition and the calibration curve methods.