A NOVEL 12-MEMBERED TRIAZAOXAMACROCYCLE-N,N',N''-TRIACETIC ACID INDICATOR FOR COLORIMETRIC DETERMINATION OF CALCIUM

The synthesis of a novel chromogenic triazaoxamacrocycle bearing three acetic acid groups and a 2,4,6-trinitroanilino chromophore, for gener ation of a spectrophotometric response, is described. As determined by potentiometric titration conducted in water, tetraionizable chromoion ophore 4 forms a rather weak 1:1 complex with calcium (K(s) = 9.5 X 10 (2) M-1) but exhibits very high selectivity for Ca2+ over Mg2+ at neut ral pH. Cation responses at pH 7.0, 8.0, 9.0, and 10.0 are determined. The response of 4 to calcium is linear from 2 x 10(-5) to 1 x 10(-4) M Ca2+.