The complex formation equilibria involved in the binary and ternary sy
stems M(II)-sulpha and M(II)-phen-sulpha were investigated by potentio
metric titrations at 25 degrees C and a ionic strength of 0.1 N NaNO3
(M = Cu, Ni, Co, Zn; sulpha = sulphamethoxazole; phen = phenanthroline
). The stability constants of the binary and ternary complexes follow
the order of Irving and William. The formation of the ternary complex
is discussed in terms of the binary species. The mode of chelation was
ascertained by conductivity measurements.