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Eco-friendly solid-contact ion selective electrode was fabricated and optimized for the determination of flavoxate hydrochloride in presence of its main metabolite. The process is based on carbon screen printed electrode and polyvinyl chloride polymeric sensing membrane. The first optimization step involved the ionophore selection through screening various ionophores, where calix[4]arene showed the highest affinity towards flavoxate. The second step, a graphene nanocomposite interlayer was employed as the ion-to-electron transducer between the carbon electrode and the polymeric ion sensing membrane. The graphene layer decreased the potential drift down to < 500 μV/h and improved the electrode stability.

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Two microsized graphite-design sensors based on ionophore technique, polyvinyl chloride carboxylated (PVC-COOH) and β-cyclodextrin (β-CD), are used for fabrication of two membrane sensors for the two studied drugs, metronidazole (MZ), sensor 1, and spiramycin (SP), sensor 2. Fast and stable Nernstian responses near 1x10-5-1x10-3 M for MZ and 1x10-5-1x10-2 M for SP over pH range 5.5-7.5 for the two electrodes reveal the performance characteristics of these electrodes which have been evaluated according to IUPAC recommendations. The aim of this work is to develop a new, simple, accurate and precise method for the determination of MZ and SP in their binary mixtures, which can be applied in routine quality control. The method is successively applied for the determination of the two drugs in their pharmaceutical formulations. Validation of the method according to the quality assurance standards shows suitability of the proposed electrodes for the use in the quality control assessment of these drugs. The recovery percentages for the determination of the two drugs by the two proposed selective electrodes are 99.86 ± 0.249 % and 99.69 ± 0.856% for sensors 1 and 2, respectively. Statistical comparison between the results obtained by this method and the reported one is done and no significant difference is found.

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Metronidazole (MZ) is an anti-infective drug used in the treatment of anaerobic bacterial and protozoa infections in humans. It is also used as a veterinary antiparasitic drug. Spiramycin (SP) is a medium-spectrum antibiotic with high effectiveness against Gram-positive bacteria. Three simple, sensitive, selective and precise spectrophotometric methods were developed and validated for the simultaneous determination of MZ and SP in their pure form and in pharmaceutical formulations. In methods A and B, MZ was determined by the application of direct spectrophotometry and by measuring its zero-order (D(0)) absorption spectra at its λ(max) = 311 nm. In method A, SP was determined by the application of first derivative spectrophotometry (D(1)) and by measuring the amplitude at 218.3 nm. In method B, the first derivative of the ratio spectra (DD(1)) was applied, and SP was determined by measuring the peak amplitude at 245.6 nm. Method C entailed mean centering of the ratio spectra (MCR), which allows the determination of both MZ and SP. The methods developed were used for the determination of MZ and SP over a concentration range of 5-25 µg ml(-1). The proposed methods were used to determine both drugs in their pure, powdered forms with mean percentage recoveries of 100.16 ± 0.73 for MZ in methods A and B, 101.10 ± 0.90 in method C, 100.09 ± 0.70, 100.02 ± 0.88 and 100.49 ± 1.26 for SP in methods A, B and C, respectively. The proposed methods were proved using laboratory-prepared mixtures of the two drugs and were successfully applied to the analysis of MZ and SP in tablet formulation without any interference from each other or from the excipients. The results obtained by applying the proposed methods were compared statistically with a reported HPLC method and no significant difference was observed between these methods regarding both accuracy and precision.

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