Validated Potentiometric Sensors for Determination of Ramipril in Pharmaceuticals and Biological Fluids using in situ Screen Printed and Carbon Paste Electrodes

In this study, electroactivity and performance characteristics of in situ screen printed (ISPEs) and carbon paste (ICPEs) electrodes with different types of ion pairing agents were studied in order to evaluate ramipril (RAM) concentrations in pure solutions, pharmaceutical formulations and biological fluids. The surface analysis of the electrodes was carried out using scanning electron microscopy and energy dispersive X-ray analyzer. The electrodes showed linear responses with good Nernstian slopes of 59.6 +/- 0.6 and 58.8 +/- 0.8 mV/decade over the concentration range from 5 x 10(-7) to 1 x 10(-2) M for ISPE and ICPE modified with phosphomolybdic acid (PMA) (electrodes I and III), respectively. At the same time, for ISPE and ICPE modified with phosphotungstic acid (PTA) (electrodes II and IV) slope values of 59.3 +/- 0.9 and 58.3 +/- 0.9 mV/decade, respectively, were obtained. Also, the two types of electrodes modified with PMA and PTA provided response times of about 5 s for ISPEs and 6 s for ICPEs and exhibited lifetimes of 99 and 92 days for electrodes I and II, respectively, and 68 days for the both paste electrodes (III and IV) in the pH range from 2 to 5 for all the proposed electrodes. They showed high thermal stability where the isothermal coefficients were found to be 0.5 x 10(-3) and 1.0 x 10(-3) V/grad for electrodes I and II, respectively, and 0.8 x 10(-3) and 0.9 x 10(-3) V/grad for electrodes III and IV, respectively. Selectivity coefficients of RAM sensors relative to a number of potential interfering materials were investigated. The direct potentiometric determination of ramipril using the prepared sensors gave recoveries between 99.4-99.6, 99.5-99.8, 99.3-99.5 and 99.5-99.6% using electrodes I, II, III and IV, respectively. The developed method was found to be simple, precise and accurate when compared to the reported methods. Method validation parameters were optimized according to IUPAC recommendations.