Quantitative Determination of Dyes in Textile Fibers Part I : Cationic and Nonionic (Disperse) Dyes in Polyacrylonitrile Polymers

Cationic and nonionic dyes in polyacrylonitrile fiber are determined spectrophotometrically by dissolving the dyed fiber in dimethylsulfoxide (DMSO) acidified with p-toluene-sulfonic acid. The absorptivity and stability of the cationic dye dissolved in DMSO depend upon the acidity of the solvent and exhibit a maximum in the pH range of 2.4-4.0. In the absence of acid some cationic, e.g., triarylmethane, dyes fade rapidly in DMSO or dimethylformamide (DMF). The fading is not always reversible upon acidification. The lightfastness of cationic dyes is higher in DMSO than in DMF containing the same amount of p-toluenesulfonic acid.