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Two fast, accurate and selective stability-indicating methods were developed and validated for the simultaneous determination of bisoprolol, perindopril and three of their possible degradation products. The first proposed method was a gradient reversed phase-high-performance liquid chromatography (HPLC) method, whereas the second was a capillary electrophoresis method. The structures of the obtained degradation products were elucidated using infrared and mass spectrometry. They were also confirmed to be either a drug impurity in the British Pharmacopoeia or a precursor to such impurity. The linearity for bisoprolol and perindopril was achieved in the range of 1–20 μg mL−1 and 5–30 μg mL−1 for HPLC and capillary electrophoresis methods, respectively. The proposed methods were validated according to the International Conference on Harmonisation guidelines. The HPLC method proved to be more sensitive and succeeded in the quantitative determination of the obtained degradation products. Also, it was able to quantify perindopril impurity up to three times lower than the desired limit set by the British Pharmacopoeia. They were successfully employed in the determination of bisoprolol and perindopril in their combined pharmaceutical formulation.

The objective of this study is to fabricate solid-contact ion selective electrodes (SC-ISEs) that have long term stable potential. Various conducting polymers such as polyaniline and its derivatives have been successfully employed to improve the potential stability in SC-ISEs. Recently, the role of hydrophobicity at the interface between the conducting polymer solid contact and the ion sensing membrane has been investigated and figured out that the hydrophobic interfaces preclude water layer formation that deteriorate the SC-ISEs potential stability and reproducibility. In this work, a hydrophobic polyaniline derivative was fabricated on the surface of a glassy carbon electrode by electropolymerization of perfluorinated aniline monomers in acidic solution. The electropolymerized hydrophobic polymer was characterized by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. The fabricated electrode was employed for determination of midazolam—a model drug-in pharmaceutical formulation without prior extraction. The SC-ISEs performance was optimized, and the potential drift was compared to control SC-ISEs, the SC-ISE linear range was 1 × 10–6–1 × 10–2 M, LOD was estimated to be 9.0 × 10–7 M, and potential drift was reduced to 100 μV/h.