Chlorophosphonazo mA (CPA-mA) forms blue complexes with rare earth elements in acidic medium. Chlorophosphonazo mA can be used for the determination of rare earth elements[1].
References:
[1].Hong Zhao, et al. Complex formation reactions of heavier rare earths with meta-acetyl-chlorophosphonazo (CPAmA). Inorganica Chimica Acta. Volume 134, Issue 1, 2 November 1987, Pages 159-163.
















