Simultaneous estimation of recently FDA approved co-formulated ophthalmic solution benoxinate and fluorescein:...

Nine simple, cost-effective, and sensitive spectrophotometric methods were developed to simultaneously assay benoxinate HCl and fluorescein sodium in their co-formulated eye drops without barring common excipients. A direct UV spectrophotometric method (method I) was developed for their FLU assay at 481 nm over the concentration range of 0.6-10.0 μg mL^-1. Meanwhile, BEN was assayed over the concentration range of 1.0-25.0 μg mL^-1 by different UV based methods, namely, conventional dual-wavelength method (DW) (method II), first derivative¹D spectrophotometry (method III), second derivative²D spectrophotometry (method IV), ratio spectra difference spectrophotometry (method V), the first derivative of ratio spectra (method VI), ratio subtraction method (method VII), isosbestic point method (ISP) (method VIII) and absorption factor method (method IX). The performance of the proposed methods was assessed relying on the correlation coefficients, relative standard deviations, and limits of detection and quantitation. The variance ratio F-test and Student t-test showed no significant differences between the obtained results of the developed methods and those of reference methods. The proposed methods were also applied to determine studied drugs in commercial eye drops and aqueous humor.