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The work refers to the already published modification of widely used method for anionic active agents determination which concerns the replacement of the mixed indicator, consisting of Acid Blue 1 and carcinogenic Dimidium Bromide, applied in the International Standard ISO 2271:1989 with solvatochromic dye i.e. 5-(3-bromo-4-hydroxy-5-methoxyphenyl)-7,7-dimethyl-7H-indolo[1,2-a]quinolinium perchlorate (1). The value of pK a  for examined dye (1) amounts to 6.59 thus the influence of different pH values of the probes on the analysis results was studied i.e. precision of determination of titration endpoint and the same the result of the quantitative analysis. The change of pH for aqueous and apparent pH for organic phase were determined during the titration process. It was shown that there is no effect of the pH change in its range varying from 3.5 to 5 on the results. The modification of the method for the probes which pH do not fit to the range mentioned above is presented.

tenside surfactants detergents

5-(3-Bromo-4-hydroxy-5-methoxyphenyl)-7,7-dimethyl-7H-indolo[1,2-a]quinolinium Perchlorate as a New Indicator for Anionic Surface Active Agents Determination: Part II. Influence of pH on the Titration Results