Indirect fibre-optic colorimetric determination of ascorbic acid using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol and cloud point extraction

Abstract

A new method has been developed for the indirect determination of ascorbic acid (AA) in commercial syrup preparations based on cloud point extraction (CPE) separation and preconcentration, and determination by molecular absorption spectrometry. The colorimetric method was based on the reduction of Fe(III) to Fe(II) and complexation of Fe(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP), followed by its extraction into Triton X-114. Selectivity of the method was increased with the use of EDTA as a masking agent. The absorbance was measured at 742 nm. Various influencing factors on the separation and preconcentration of AA have been investigated systematically, and the optimized operation conditions were established. The proposed method allows the determination of AA in the range 5-200 µg L(-1) with a relative standard deviation of 3.0%. The detection limit was found to be 0.9 µg L(-1) for AA. This method has been applied to the determination of ascorbic acid in commercial pharmaceutical preparations.