Spectroscopic quantification of cyclopentolate using an erythrosine-based resonance rayleigh scattering strategy: application to ophthalmic formulations

Cyclopentolate (CYP), an antimuscarinic (anticholinergic) agent, is pharmacologically employed in ophthalmology to induce cycloplegia (temporary paralysis of the ciliary muscle) and mydriasis (pupil dilation) for diagnostic and therapeutic procedures, including ocular examinations and surgeries. This study establishes a spectrofluorimetric method for quantifying CYP in ophthalmic solutions based on Resonance Rayleigh Scattering (RRS) signal modulation. The approach exploits the formation of an ion-associate complex between CYP and the dye erythrosine, which induces a measurable RRS enhancement. Critical experimental parameters governing the complexation and subsequent RRS response were systematically investigated and optimized. Under these established optimal conditions, a linear correlation existed between the enhanced RRS intensity and CYP concentration across the range of 40 to 1500 ng/mL. The method demonstrated a detection limit (LOD) of 13 ng/mL and a quantification limit (LOQ) of 39.5 ng/mL. Successful application to the assay of cyclopentolate in commercial eye drop formulations confirmed the method's accuracy and precision. This RRS-based methodology utilizing erythrosine presents a straightforward, rapid, cost-effective, and environmentally favorable option for routine quality control and monitoring of CYP in pharmaceutical preparations.