The spectrophotometric determination of micromolar concentrations of Co 2+ using o-phenanthroline

Abstract

Co 2+ and o-phenanthroline formed a 1:3 complex with absorption maxima at 346, 332, 313, and 301 nm. The complex obeyed Beer's Law at the first three maxima. Standard curves constructed by monitoring the E 346 at different concentrations of Co 2+ had a maximum sensitivity of about 1 μ m Co 2+. At this concentration of Co 2+ the Δ E 346 was 0.003 absorption units. This assay was not affected greatly by Ca 2+, Mg 2+, K +, Na +, or Tris. Erbium ions (Er 3+) produced a small, nonspecific increase in absorbance at all wavelengths. Zn 2+ also formed a complex with o-phenanthroline with maxima at 343, 328, and 313 nm. The absorbance of the Zn 2+- o-phenanthroline complex was about 10% that of the Co 2+- o-phenanthroline complex at 346 nm, but was still sufficient to cause interference at Zn 2+ concentrations above 10 μ m.