POLYELECTROLYTE TITRATION USING FLUORESCENT INDICATOR .1. DIRECT TITRATION OF ANIONIC AND CATIONIC POLYELECTROLYTES WITH 10(-4)N STANDARD SOLUTIONS

The polyelectrolyte titration, which was originally called colloid titration, is based on the stoichiometric reaction between positively charged colloidal particles and negatively charged ones. In the conventional method, the metachromatic color change of the indicator, toluidine blue, from blue to red-purple has been applied for the determination of the end point in the titration. 2.5 X 10(-3) N potassium polyvinylsulfonate (KPVS) is usually used as the standard titrant. In this work, fluorescent indicators such as 6- (p-toluidino) -2-naphthalene sulfonate (TNS), acridine orange, etc., have been introduced. The fluorescence intensity was measured using the spectrophotometer equipped with magnetic stirrer and connected with a vinyl tube attached to the hand piston burette. For example, TNS is practically nonfluorescent, but it exhibits strong fluorescence when it is bound to a cationic polyelectrolyte (CP). The fluorescence of the TNS-CP complex is diminished by titration with KPVS standard solution since TNS is liberated from the complex by substitution with KPVS. After the equivalent point, the fluorescence intensity becomes constant and the end point can thus be detected by that point. It has been elucidated that the very dilute standard solution like 1 X 10(-4) N can be used because the sensitivity of fluorescence detection is extremely high. (C) 1993 John Wiley & Sons, Inc.