Dichlorofluorescein and Potassium Chromate as Indicators in the Argentometric Estimation of Salt in Butter

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Potassium chromate has long been used as the indicator in the argentometric estimation of the sodium chloride content of solutions prepared in the analysis of butter according to the method of Kohman (4) as recommended by the Subcommittee on Butter Analysis of the American Dairy Science Association (1). Recently, Bryant (2) has suggested the substitution of the adsorption indicator, dichlorofluorescein, for potassium chromate as the titration indicator. Whereas potassium chromate solutions undergo a color change from yellow to orange-red and thence brick-red, upon the addition of silver nitrate, salt solutions containing dichlorofluorescein undergo color transition from greenish-yellow fluorescent through whitish opalescent to pink. Under certain conditions the transition of the yellow to orange-red color in the chromate-silver nitrate reaction has not been considered sufficiently critical to permit sharp distinction of the colors. This lack of distinction may easily lead to utilization of an improper end point in the reaction, with accompanying error in the analysis, t tunziker specifically cautions, for example, against excess titration (3). Bryant has observed that the color change from white or whitish appearance to pink state is sudden, and, further, that the results obtained with the fluorescein dye are less (approximately 0.1 per cent salt equivalent) than when potassium chromate is used. The regults obtained using the two indicators, dichlorofluorescein and potassium chromate, when determining the salt content of solutions prepared in the routine analysis of butter received at the Department of Dairy Industry, and in experimental comparisons, are presented to indicate the differences which occur by use of the two methods.