A new selective metallochromic reagent for the detection and chelatometric determination of calcium

A new reagent, Calcichrome, which gives a highly sensitive colour reaction with calcium ions in alkaline solution, has been synthesised. Neither barium, strontium nor magnesium react with the reagent, which is therefore proposed as a selective spot-test reagent for calcium. In addition, Calcichrome may be used as a metallochromic indicator for the accurate complexometric titration of calcium in the presence of at least twelve-fold amounts of barium. Trans-1:2-diaminocyclohexane-N:N:N':N'-tetra-acetic acid is used as titrant since it is the only complexan available which is sufficiently selective in its reactivity towards calcium and barium.