Evaluation of colour changes of screened acid-base indicators

Based on computer-assisted calculations, six screened indicators were prepared and used for visual titration end point indication. Three of them were evaluated in terms of objective colour characteristics. Their colour changes were characterized in the CIE-xy (1931) international colorimetric system, by the Helmholtz coordinates, complementary Qx, Qy coordinates, perceptibility and course of the ΔJ/ΔpH = f(pH) function. In addition, new indices were introduced, viz. partial quality indices IE, Ip and Im, related with the colour difference between the two indicator species (IE), their colour purity (Ip) and the experimenter's ability to remember the colour in the titration end point (Im). Summed up, the three indices constitute the total quality index of the chemical indicator It. These indices were employed for comparing the single and the corresponding screened indicators.