Determination of calciun in silicon iron by discoloring spectrophotometry with Picramine CA

A sensitive spectrophotometric method was developed to determine calcium, based on the discoloring reaction of calcium-Picramine CA system in pH 11.0 NH3·H2O-NH4Cl medium and linear relationship of the discoloring degree with the certain concentration range of calcium. The factors such as absorption spectra、 acidity、 concentrations of reagent、 influence of coexisting ions on the reaction are discussed, and the optimal reaction conditions are established. Beer′s law was obeyed in the range of 8～90 μg/25 mL for calcium with an apparent molar absorptivity of 1.26×104 L·mol-1·cm-1. The proposed method has been applied to the determination of calcium in silicon iron. The RSDs (n=5) are between 1.4% and 2.1%.