Lotfy H.M.Saleh S.S.Hassan N.Y.Salem H.Analytical Chemistry DepartmentFaculty of PharmacyCairo UniversityKasr-El Aini Street11562 CairoEgypt; Analytical Chemistry DepartmentFaculty of PharmacyOctober University for Modern Sciences and Arts (MSA)11787 6th October CityEgypt2020-01-092020-01-09201413861425https://doi.org/10.1016/j.saa.2014.01.130PubMed ID 24589996https://t.ly/JXvd5ScopusMSA Google ScholarThis work represents the application of the isosbestic points present in different absorption spectra. Three novel spectrophotometric methods were developed, the first method is the absorption subtraction method (AS) utilizing the isosbestic point in zero-order absorption spectra; the second method is the amplitude modulation method (AM) utilizing the isosbestic point in ratio spectra; and third method is the amplitude summation method (A-Sum) utilizing the isosbestic point in derivative spectra. The three methods were applied for the analysis of the ternary mixture of chloramphenicol (CHL), dexamethasone sodium phosphate (DXM) and tetryzoline hydrochloride (TZH) in eye drops in the presence of benzalkonium chloride as a preservative. The components at the isosbestic point were determined using the corresponding unified regression equation at this point with no need for a complementary method. The obtained results were statistically compared to each other and to that of the developed PLS model. The specificity of the developed methods was investigated by analyzing laboratory prepared mixtures and the combined dosage form. The methods were validated as per ICH guidelines where accuracy, repeatability, inter-day precision and robustness were found to be within the acceptable limits. The results obtained from the proposed methods were statistically compared with official ones where no significant difference was observed. � 2014 Elsevier B.V. All rights reserved.EnglishAbsorption subtraction methodAmplitude modulation methodAmplitude summation methodChloramphenicolDexamethasoneIsosbestic pointAmplitude summation methodChloramphenicolDexamethasonesIsosbestic pointSubtraction methodAntibioticsChlorine compoundsElectromagnetic wave absorptionMixturesSpectrophotometryAmplitude modulationbenzalkoniumchloramphenicoldexamethasonedexamethasone 21-phosphatedrug combinationeye dropsimidazole derivativepreservativetetryzolineanalogs and derivativeschemistrycomparative studydrug combinationprincipal component analysisproceduresspectrophotometryvalidation studyBenzalkonium CompoundsChloramphenicolDexamethasoneDrug CombinationsImidazolesOphthalmic SolutionsPreservatives, PharmaceuticalPrincipal Component AnalysisSpectrophotometryArticlehttps://doi.org/10.1016/j.saa.2014.01.130PubMed ID 24589996