2-(2-thiazolylazo)-4-methoxyphenol and 2-(2-thiazolylazo)-5-methoxyphenol as metal-ion indicators

2-(2-Thiazolylazo)-5-methoxyphenol (TAMR) and 2-(2-thiazolylazo)-4-methoxyphenol (TAMH) are shown to be good indicators for the titration of many metal ions with EDTA. TAMH is better and more widely applicable than TAMR. The acid dissociation constants have been determined by spectrophotometry. The effect of pH on the absorbance of the indicators and metal-indicator complexes is reported.