Determination of the acid dissociation constant of Nile blue and metanil yellow by the solution scanometric method and comparison with spectrophotometric results

Correctly determination of the acidity constant of acidity constants cause to perception and quantitative analysis of chemical phenomena such as reaction time, activity, absorption and bio transmissions [1]. Determination of the acidity constant was studied by different methods such as spectrophotometry, potentiometric titration, Proton magnetic resonance spectroscopy, Fluorescence spectrophotometry and chromatography [2, 3]. In this study was applied scanometric method for the determination of the acid dissociation constant of the two indicator dyes (Nile blue (NB) and metanil yellow (MW)). The method is based on the RGB color model, which specifies how much of each color is formed of red, green, and blue colors. Metanil yellow is one of the non-permitted dyes used for food coloring in India. Metanil yellow is a monoazo dye, the sodium salt of m-[(p-anilinophenyl) azo] benzenesulphonic acid. Its toxicity and mutagenicity have been assessed. Nile blue (or Nile blue A) is a fluorescent dye and a stain that used in biology and histology. Electrochemical polymerization of the Nile blue is used for the amperometric measurement of hemoglobin.The comparison between the current traditional UV-Vis spectrophotometry methods was studied and the results revealed similar trends in both methods. For evaluation acidity constant of the cited indicators, using spectrophotometric data, the Hypspec program was employed. The calculated pKa values of the cited indicators by solution scanometry and spectrophotometric methods are in agreement. The corresponding distribution diagrams were depicted by Hyss 2009.