PVC membrane bulk optode incorporating 4-nitrobenzo-15-crown-5 and sodium tetrakis(1-imidazolyl) borate for the pico-molar determination of silver ion in pharmaceutical formulation

Silver ion (Ag⁺) is of harmful effects to both environment and human health. Ag⁺ soluble compounds and salts is used in treating mental illness, epilepsy, nicotine addiction, gastroenteritis, and infectious diseases, including syphilis and gonorrhea, and as anti-infective dermatological agent for controlling nose bleeding. However, high Ag⁺ doses cause several harmful effects to human health such as irreversible pigmentation of skin and eye, and problems to liver and kidney. A bulk membrane Optode is proposed in this work to measure the Ag⁺ concentration in the pharmaceutical formulations. The membrane optode is prepared from the ionophore 4-nitobenzo-15-crown-5, the ion-exchanger sodium tetrakis (imidazolyl) borate, the plasticizer o-nitrophenyl octyl ether, and the chromoionophore ETH 5294; these components are dissolved in the PVC/THF slurry to form the membrane. The optode is studied by atomic force microscope and UV–visible spectrophotometer, and its spectrum exhibits two maximum wavelengths of 550 and 665 nm, and response for Ag⁺ at these maximum wavelengths is reproducible in the concentration range of 10^–11 to 10^–8 M using acetate buffer of pH 5.0, with very low detection limit of 8.8 × 10^–12 M. The most important feature in this work is the selectivity improvement for Ag⁺ over all interfering ions; the selectivity coefficient logarithm \({logK}_{Ag+, cation}^{opt}\) ${\mathit{logK}}_{Ag+,cation}^{\mathit{opt}}$ is found to be − 4.3 for Cu²⁺, − 5.6 for Ni²⁺ and − 5.0 for Cd²⁺. The response mechanism is studied by FTIR, and it depends on ion-exchange of Ag⁺ and sodium imidazolyl borate, followed by the host–guest complexation between Ag⁺ and the crown ionophore, which is accompanied by concomitant deprotonation of the chromoionphore. The optode has a response time of 2–3 min within lifetime of 10 days with the same response. The optode can be applied successfully for Ag⁺ determination in the pharmaceutical formulation, PinkEye Relief^® eye drop, which is used for treating inflammation, redness and water discharge of the eye; the high recovery and low standard deviation of the results using calibration curve method confirm the accuracy and precision of the proposed optode for its application in real samples.