Determination of iron in rainwater, lakewater, and tapwater by high performance capillary electrophoresis after precolumn complexation with 1,10-phenanthroline

A high performance capillary electrophoresis method has been developed for direct determination of iron levels in rainwater, lakewater, and tapwater. The absorbance of Fe(II)-1,10-phenanthroline complex was measured at 270 nm instead of at 508 nm. It also has even stronger absorbances at 200 nm, 226 nm, and 270 nm. It was found that the molar absorptivity of Fe(II)-1,10-phenanthroline complex was highest at 270 nm and was 8-fold higher than at 508 nm. Different buffer systems have been tested and their effects on the separation of Fe(II)-1,10-phenanthroline complex and 1,10-phenanthroline were tabulated. A 50 mM NH₄ Ac-HAc at pH 5 is ideal for this experiment. Under the ideal separation and detection conditions, a detection limit of 5 × 10⁻⁹ M iron with S/N = 5 can be obtained. In the iron concentration range of 1.0 × 10⁻⁷ M − 4 × 10⁻⁶ M, the linear regression equation for iron concentration vs. CE signal is: C_Fe(μM) = 1.00 × 10⁻⁴ A + 2.86 × 10⁻³ with 14 data points, and R² is 0.9997. The iron level in rainwater, lakewater, and tapwater ranges from 2.5 × 10⁻⁷ M to 5.5 × 10⁻⁷ M. Recovery tests range from 90–107%, which means that the method can be quantitatively used for determination of iron level in natural water.