Determination of Anionic Polyelectrolytes Using a Photometric Titration with Crystal Violet as a Color Indicator

Abstract.

 The reaction of the cationic dye, crystal violet (CV), with anionic polyelectrolytes such as potassium poly(vinyl sulfate) (PVSK) results in a decrease in the absorbance of CV at the maximum absorption wavelength (590 nm). This change in the absorption spectra of the CV has already been applied to the determination of anionic polyelectrolytes using flow injection analysis (FIA). In this paper, CV was applied as an indicator in the determination of anionic polyelectrolytes such as PVSK and carageenan by photometric titration, using a poly (diallyldimethylammonium chloride) (Cat-floc) solution as a titrant. The end-point of the titration is detected as the turning point of the titration curve. A linear relationship exists between the concentration of anionic polyelectrolyte and the end-point volume of the titrant in the concentration range of 0 to 5 × 10⁻⁵ M for PVSK and carageenan. The effects of the concentration of CV and coexisting electrolytes in the sample solution and the effect of pH of the sample solution on the degree of change of absorbance at the end-point were also examined.