1978 Volume 27 Issue 7 Pages 429-434
Purified Xylenol Orange (XO) and semi-Xylenol Orange (SXO) are tested as metallochromic indicators in the direct EDTA titration of 9 metals and as spectrophotometric reagents for the determination of zirconium and bismuth. The results are also compared with those reported previously with commercial products of XO, which generally contain appreciable amounts of SXO. XO can be used as an excellent indicator for all the metals investigated, except for indium, since it forms intensely colored (reddish-violet or blue violet) complexes with the metals and gives a sharp color transition at the equivalence point of the titration. On the other hand, SXO, which forms pink or pink-red metal complexes, can also be employed as an indicator for zirconium, thorium and bismuth, but rather poor end-points are observed in the titrarion of the other metals. The use of pure XO is therefore preferable in the routine back-titrations with a standard bismuth, lead or zinc solution. In the spectrophotometric determination of zirconium and bismuth with XO, the optimal conditions for the determination and the spectral properties of the complexes formed are considerablly different from those reported previously. It should be noted that, as a spectrophotometric reagent, SXO is much superior to XO in sensitivity, although both reagents can be conveniently used for the determination of these metals.
