Sulfophthalein dyes

Sulfophthalein dyes are adsorbed better than xanthene ones. The reason may be both in a smaller size of the molecules, and in the presence of fully charged sulfonate group in the structure of sulfophthalein dyes which promotes adsorption. In the last case, a superfluous positive charge of the film material, probably due to unbounded lysine and argenine groups of PtS, can be assumed. The increased dye contents may be also explained by the fact that sulfophthalein dyes were adsorbed from water-ethanol solutions that could influence the distribution of the dyes between phases. Besides, introduction of ethanol reduces the dielectric constant of the solution, that, in turn, can increase permeability of PEMs [1-4] and, as a consequence, may lead to increased dye loading into PtS/CMC films. 

One of the factors influencing adsorption is electronegativity of substituents in the dye molecules. The influence is noticeable for sulfophthalein dyes (Table 1). However, for xanthene dyes such pattern is not observed, and the factors influencing their adsorption cannot be revealed. 

Yamamoto, K. Adachi, K. Interaction between sulfophthalein dyes and chitosan in aqueous solution and its application to the determination of surfactants. Anal. Sci. 2003,19,1133-1138. 

Tananaiko, M. M. Gorenshtein, L. I. Comparative stndy of complexes of silver with 1,10-phenanthro-line and sulfophthalein dyes. Ukr. Khim. Zh. 1981, 47, 771-773 Chem. Abstr. 1981, 95,108025. 

Sedmikova, A. Gasparic, J. Study of the use of sulfophthalein dyes for the determination of drugs by means of ion-pair extraction spectrophotometry. Ceska Slovenska Farm. 1996, 45, 132-138. Chem. Abstr. 1996,125, 123890. 

Among the great variety of organic chromophores such as azo dyes, nitrophenols, phthaleins, sulfophthaleins, aniline-sulfophthaleins, triphenylmethane dyes, polymethines, and others, only a few have so far been considered to be useful and applied to sensor technology (Table l)25 34. Important characterization parameter of pH indicator is its pKa value ... 

Individual pH Indicators. The most commonly used pH indicators include azo dyes, nitrophenols, phthaleins, and sulfophthaleins. Varying the substituents on the chromophores yields pH indicators with different transition ranges, and the complete pH range between 0 and 14 can thus be covered, as shown in Table 5.17 and Figure 5.2. Introducing acid groups (sulfo or carboxyl) leads to water-soluble indicator dyes. 

Adsorption of sulfophthalein and xanthene dyes by protamine sulfate/carboxymethylcellulose (PtS/CMC) layer-by-layer (LbL) films has been studied. The adsorbed amount of a dye depends on its nature, solvent, conditions of polyelectrolyte multilayers (PEMs) preparation. Addition of ethanol into solution and preliminary drying of PEMs increase adsorption of the dyes. Kinetics of a dye release from (PtS/CMC)2o films in acidic solution (pH 3.0) has been investigated. 

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