Flow-injection, on-line concentrating and flame atomic absorption spectrometry for indirect determination of ascorbic acid based on the reduction of iron(III)

Abstract

A flow-injection flame atomic absorption spectrometry is proposed for indirect determination of ascorbic acid based on its reducing action to Fe(III). The Fe(II), produced by the reduction of Fe(III), is on-line adsorbed on a mini-column filled with cation-exchange resin to concentrate, then is eluted reversely by 3 mol l −1 nitric acid to nebulizer and is measured by flame atomic absorption spectrometry, while the excessive Fe(III) reacts with NH 4F to form anion [FeF 6] 3− and passes through the mini-column to be waste. When reaction and concentrating time is 60 s, the absorbance of Fe(II) is proportional to the concentration of ascorbic acid in the range from 0.1 to 50 mg l −1. The analytic frequency is 30 samples per hour. This method has been applied to the determination of ascorbic acid in Vitamin C tablets, Vitamin C injection, vegetables and fruit juice. The results obtained in the analysis agreed well with those provided by iodimetry.