Sensitive spectrophotometric determination of ascorbic acid in fruit juices and pharmaceutical formulations using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP)

A simple and very sensitive method has been developed for the determination of ascorbic acid based on the oxidation of ascorbic acid to dehydroascorbic acid by iron(III), followed by a complexation of iron(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(Br-PADAP). The iron((II) complex is formed immediately, with absorption maxima at 560 and 748 nm and a molar absorptivity of 1.31 x 10(5) l mole(-1)cm(-1) and 5.69 x 10(4) l mole(-1)cm(-1), respectively. The ascorbic acid determination is possible with a linear range up to 2.4 mu g ml(-1), a calibration sensitivity of 0.744 ml mu g(-1) at 560 nm and 0.323 ml mu g(-1) at 748 nm, and a detection limit of 15 ng ml(-1) and 44 ng ml(-1), respectively. The procedure was used for the ascorbic acid determination in several fruit juices and pharmaceutical formulations. The results demonstrated a good precision (R.S.D. < 1%) and are in agreement with those obtained with others methods. The Br-PADAP method proposed is six times more sensitive than the method using the iron(II)-1,10-phenanthroline system.