A stability-indicating potentiometric platform for assaying Metoprolol succinate and felodipine in their tablets and human plasma

Solid contact electrodes are prevalent in analytical applications due to their superior performance compared to traditional electrodes. Nonetheless, these electrodes have been observed to develop a water layer, which compromises their stability. In this study, we introduce an innovative solid contact ion selective electrode designed to mitigate this issue by incorporating multi-walled carbon nanotubes. This system was utilized for potentiometric sensing of metoprolol and felodipine. Furthermore, molecular imprinted polymer was developed to enhance selectivity for determination of felodipine. The electrode modified with multi-walled carbon nanotubes was employed for the quantification of metoprolol, exhibiting a Nernstian slope of 55.23 mV/decade over a linear concentration range of 1.0 × 10^{- 7} to 1.0 × 10^{- 2} mol L^{- 1}, at a pH of 7.0. The molecularly imprinted polymer-modified electrode was utilized for the determination of felodipine, showing slope of 56.089 mV/decade across a linear range of 1.0 × 10^{- 7} to 1.0 × 10^{- 4} mol L^{- 1}, at a pH of 3.0. Detection limits for both sensor were less than 8.0 × 10^{- 8} mol L^{- 1}. The developed sensors were successfully utilized for the quantification of the aforementioned drugs in pharmaceutical tablets, in human plasma samples and in the presence of their degradates. The proposed approach showed a better linearity range and a lower limit of detection for metoprolol quantification compared to its reported potentiometric methods. Moreover, it was the first one to use such an electrochemical technique for felodipine detection.