Double-peak-double-wavelength spectrophotometric determination of trace selenium in salt

A new method for determination of trace selenium by double-peak-double-wavelength spectrophotometry was developed.It was based on the reaction between Se(IV) and magneson I to form a stable complex(1∶6) in NaHCO3-NaOH buffer solution at pH 10.8.The complex exhibited a positive absorption peak at 448 nm and a negative absorption peak at 560nm.Beer's law was obeyed in the concentration range of 0～1.4 μg/mL for selenium.The apparent molar absorptivity was found to be 3.89 × 104 L·mol-1·cm-1.The limit of detection was 0.096 μg/mL.The method was applied to determine selenium content in salt fortified with selenium.RSD was 0.43%(n = 5),and the average recovery was 99.4%.