Spectrophotometric determination of calcium in silicon iron with chlorophosphonazo III

The coloring reaction between chlorophosphonazoⅢ and calcium was studied,and a determination method of calcium in silicon iron by spectrophotometry was established.The optimal reaction conditions were investigated and obtained.The results showed that in NH3·H2O-NH4Cl buffer solution at pH 10.0,the calcium could form green complex with chlorophosphonazoⅢ.The complex had maximum absorption at 672 nm,and the absorbency was in direct proportion to the concentration of calcium.Beer's law was obeyed for calcium in the range of 0.072-1.00 μg/mL.The detection limit of method was 0.022 μg/mL.After triethanolamine and o-phenanthroline for masking aluminum,manganese and iron was added,the proposed method was applied to the determination of calcium in common silicon iron standard samples.The results were consistent with the certified values,and the relative standard deviation(RSD) was about 2.0 %.