title: Spectrophotometric study of the effects of surfactants and ethanol on the acidity constants of fluorescein.
abstract: In the present paper, a sensitive, fast and suitable method for the calculation of pK(a) values of fluorescein is proposed. The effects of sodium dodecyl sulfate (SDS) and Triton X-100 (TX-100) as a surface-active agent on the acidic and basic forms, and the spectral properties of fluorescein were studied by the spectrophotometric method. The study was performed in sub-micelle surfactant concentration, and absorption spectra at 300-550 nm intervals were recorded. Stepwise acidity constants of fluorescein at pH range 1.50-10.00 and at constant ionic strength 0.1M and 25 degrees C were determined using DATAN program using pH-spectrophotometric titration data. The method is efficient, however the component spectra showed intensive overlapping. The calculated acidity constants of fluorescein in water at ionic strength 0.1 are pK(a1)=2.20, pK(a2)=4.30 and pK(a3)=6.43. The acidity constants of the dye in ethanol-water solution were studied by the same procedure. Effect of surfactants and ethanol on acidity constants and pure spectrum of each component are also discussed.
authors.affiliation: Chemistry Department, Faculty of Sciences, Razi University, Kermanshah, Iran.
authors.forename: Mohammad Bagher
authors.initials: MB
authors.lastname: Gholivand
authors.forename: Jahan B
authors.initials: JB
authors.lastname: Ghasemi
authors.forename: Saadi
authors.initials: S
authors.lastname: Saaidpour
authors.forename: Ali
authors.initials: A
authors.lastname: Mohajeri
mesh_terms: D000431:Ethanol; D019793:Fluorescein / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D017830:Octoxynol; D009994:Osmolar Concentration; D012967:Sodium Dodecyl Sulfate; D012996:Solutions; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D013501:Surface-Active Agents; D014867:Water
chemical_list: D005456:Fluorescent Dyes; D012996:Solutions; D013501:Surface-Active Agents; D014867:Water; D012967:Sodium Dodecyl Sulfate; D000431:Ethanol; D017830:Octoxynol; D019793:Fluorescein