Determination of complex formation constants for Cu(II)–Alizarin complexone with amines by capillary zone electrophoresis

Abstract

Complex formation constants between Cu(II)–Alizarin complexone (Cu(II)–ALC) and amines were investigated by capillary zone electrophoresis. The electrophoretic mobility ( μ ep) of Cu(II)–ALC was obtained from the migration time of 3 μg ml −1 Cu(II) in a borate buffer in the presence of 1 × 10 −3 mol dm −3 ALC of pH 9.1 at 20 kV. The μ ep value decreased with increasing amine concentration as additive in the buffer. This indicates coordination of the amines with Cu(II)–ALC. The first and second coordination equilibrium constants (dm 3 mol −1) were 1 ± 1 and (3.33 ± 0.01) × 10 6, 100 ± 1 and (4.73 ± 0.01) × 10 6, 69 ± 4 and (1.21 ± 0.07) × 10 5, 2 ± 1 and (2.74 ± 0.06) × 10 5, 150 ± 20 and 74 ± 7, 5 ± 1 and 74 ± 3, 42 ± 1 and 12 ± 3, 57 ± 1 and 9 ± 2, (2.9 ± 0.2) × 10 8 and 990 ± 90, and 7900 ± 200 and 780 ± 70 for ammonia, methylamine, ethylamine, n-propylamine, pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, imidazole, and 1-methylimidazole, respectively.