Engineering a PEG/Co-modified carbon paste electrode for highly sensitive voltammetric determination of ophthalmic antihistamine epinastine: From pharmaceutical analysis to ocular pharmacokinetics.

Abstract

Rapid and highly sensitive monitoring of epinastine in pharmaceutical formulations and biological matrices remains a significant analytical challenge, demanding methods that combine simplicity, affordability, and excellent analytical performance. In this study, a polyethylene glycol/cobalt-modified carbon paste electrode (PEG/Co/CPE) was fabricated as a novel electrochemical sensing platform for epinastine determination. The combined incorporation of PEG and Co enhanced the electrochemical response through increased electrochemically accessible surface area and modified interfacial characteristics while scan-rate studies indicated predominantly diffusion-controlled epinastine oxidation. Following systematic optimization of the experimental conditions, the proposed square wave voltammetric method exhibited two linear concentration ranges of 20.0-1400.0 nM and 2.0-100.0 μM with excellent correlation coefficients (r = 0.9998 and 0.9997, respectively). The sensor demonstrated remarkable sensitivity achieving a limit of detection of 6.5 nM and a limit of quantification of 19.8 nM. Method validation confirmed excellent analytical reliability with recoveries of 99.84 ± 0.71% and 100.26 ± 0.65% while repeatability and intermediate precision showed relative standard deviation values below 1.5%. The method was successfully applied to the determination of epinastine in a commercial ophthalmic formulation affording a recovery of 99.72 ± 0.58% whereas the standard-addition procedure yielded a mean recovery of 99.85 ± 0.11% indicating negligible matrix interference. In rabbit aqueous humor, the bioanalytical assay displayed linearity over 20.0-1400.0 nM with r = 0.9998, a detection limit of 6.3 nM, and a quantification limit of 19.1 nM while satisfying accepted criteria for accuracy, precision, and stability. Furthermore, the validated sensor enabled successful pharmacokinetic profiling following ocular administration providing reliable estimates of Cmax (27.20 ng/mL), Tmax (4.0 h), and elimination half-life (5.59 h). Collectively, the developed sensor provides a robust, cost-effective, and high-performance electroanalytical platform with strong potential for routine pharmaceutical quality control and bioanalytical pharmacokinetic applications.

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