Effect of eluent composition and pH and chemiluminescent reagent pH on ion chromatographic selectivity and luminol-based chemiluminescence detection of Co(2+), Mn(2+) and Fe(2+) at trace levels.

The alkaline-luminol/H(2)O(2)-based chemiluminescent (CL) detection of Fe(2+), Co(2+), and Mn(2+), separated with a Dionex CS5A ion chromatographic phase was studied by means of a multi-pump flow system allowing the variation of the post-column solution composition. A perchlorate gradient at pH 1.9 (with HCl) was used to separate cations partially complexed with 5.6mM oxalate present in the eluent and necessary for the chosen separation phase. A 0.91mM luminol, 3.3mM H(2)O(2) in 0.25M carbonate buffer at pH 10.5 composition was chosen as CL reagent solution. The chosen pH value warrants signal repeatability and wider linearity range although absolute signal is not maximum. The CL signal was related to the pH of the two post-column mixing solutions. Calibration plots of Co(2+) and Fe(2+) were linear in the chosen concentration range whilst a parabolic model was the best fit for Mn(2+). Detection limits were 0.24, 0.50 and 375nM for Co(2+), Fe(2+) and Mn(2+), respectively. The method was used to determine Co(2+) at trace level in commercial copper chelates used for animal feeding. A comparison with a chromatographic method with spectrophotometric detection was made giving results comparable both in absolute values and accuracy.