A Potentiometric Sensor for Determination of Doxycycline Hydrochloride in Pharmaceutical Preparation and Biological Fluids

This article focused on the construction and characteristics of novelty and sensitivity of modified carbon paste electrodes for determination of doxycycline hydrochloride (DC.HCl) in urine, serum and pharmaceutical preparations. It was based on the incorporation of α-cyclodextrine (α-CD) and multi-walled carbon nanotube (MWCNT) ionophores which improved the characteristics of the electrodes with tricresylphosphate (TCP) (electrode I) and o-nitrophenyloctylether (o-NPOE) (electrode II) as plasticizers, respectively. The constructed electrodes, at optimum paste composition, exhibited good Nernstian response for determination of doxycycline hydrochloride over a linear concentration range from 1.0 × 10^–7 to 1.0 × 10^–2 and 1.22 × 10^–7 to 1.0 × 10^–2 mol L^–1 with detection limit of 1.0 × 10–7 and 1.22 ×10^–7 mol L^–1 and with slope values of (58.7 ± 0.2) mV decade–1 and (58.0 ± 0.6) mV decade–1, for modified carbon paste electrodes (MCPEs; electrodes I and II), respectively. The results showed fast dynamic response time (about 6–7 s) and long lifetime in the range from 4 to 5 months where the response of the electrodes was not affected by pH variation within the range from 2 to 8 and 2 to 7.5 for electrodes I and II, respectively. Electrodes I and II showed high selectivity for doxycycline hydrochloride with respect to a large number of interfering species including foreign inorganic, organic species, excipients and the fillers added to the pharmaceutical preparation. The constructed electrodes were successfully applied for determination of DC.HCl in pure form, its pharmaceutical preparations and biological fluids (urine and serum) using standard addition, calibration curves and potentiometric titration methods. The results obtained using these potentiometric electrodes were comparable with those obtained using official method. The results were satisfactory with excellent percentage recovery comparable or better than those obtained by other routine methods.