EVALUATION OF COLOR QUALITY OF COMPLEXOMETRIC INDICATORS IN THE TITRATION OF NICKEL(II) WITH EDTA BY TRISTIMULUS COLORIMETRY

Trichromatic colorimetry was applied to the specification of colour changes of metallochromic indicators viz., murexide, pyrocatechol violet, bromopyrogallol red, pyropllol red and chromazurol S in the complexometric titration of Nickel(II) with ethylene-diaminetetraacetic acid (EDTA), in order to assess the quality of colour change at the equivalence point with the help of CIE L*a*b* 1976 system and the values of SCD (Specific Colour Discrimination) parameter. A screened indicator, a mixture of murexide and methylene blue in the ratio 10:1 (m/m), is proposed as an ideal indicator in this titration as evidenced by the plots of a* vs. b* and from the numerical values of standard deviation for a large number of visual titrations.