Spectrophotometric determination of zinc in salt with congo red

In presence of sodium dodecyl benzene sulfonate,Zn2+ reacts with phen and congo red in HAc-NaAc buffer solution at pH 5.7,which results in great enhancement of absorbance.Based on this fact,a new spectrophotometric method for the determination of zinc was proposed.The maximum absorption wavelength located at 568 nm,with the apparent molar absorption coefficient of 3.83×104 L/mol·cm.Beer's law was obeyed in the concentration range of 0～0.8 μg/mL for zinc.The detection limit was 11.1 μg/L.The method has been applied to the determination of zinc in fortified nutrient salt with zinc and health balance salt.The relative standard deviation was 0.95%～1.29%(n=5),and the average recovery was 98.5%～100.3%.