Determination of vitamin C by inhibition fading spectrophotometry

Based on the principle that trace vitamin C can sensitively inhibit the redox reaction between KBrO3 and 5-bromine-(2-pyridylazo)-diethylaminophenol(5-Br-PADAP),a new spectrophotometric method for determining trace vitamin C was suggested.In a medium containing 3.0 mol/L of H2SO4 at a temperature of 30 ℃,with 463 nm identified as the determination wavelength,the Beer's law was obeyed for the concentration of vitamin C ranging from 0.02 g/L to 1.5 g/L with a detection limit of 2.62×10-4 g/L.The suggested method was applied for determination of VC content in vitamin C tablets and kiwifruit with a relative standard deviation of 2.20% and 2.53%,respectively.The results of determination in this methods agreed well with those obtained by iodometry.Tests with an added standard were performed with the recovery rate equating to 98.1%～100.7%.