Determination of ascorbic acid in drug formulations by sequential injection spectrophotometry CHEN

A sequential injection spectrophotometric method is employed to the assay of ascorbic acid in drug formulations. The method is based on the reduction of Fe(Ⅲ) to Fe(Ⅱ) by the analyte, and the subsequent reaction of the produced Fe(Ⅱ) with 2,2′-dipyridyl in acidic medium (pH=5) to form a colored complex using a spectrophotometer as a detector with the monitoring wavelength at 523 nm. A univariate approach is adopted for the optimization of the experimental parameters. The results of the optimization reveals that the optimum operating conditions for this method are 0.005 mol/L Fe~(3+), 025% 2,2′-dipyridyl and a flow rate of 60 mL/min. A determination limit of 0.18 μg/mL (3σ) of ascorbic acid is obtained with a sampling frequency of 60/h using a sample volume of 300 μL. The precision is 1.61% RSD(n=11). The interference from excipient is not found, thus the method is suitable for the on-line quality control in pharmaceutical preparation. Compared with the results obtained by the standard method, the SIA method is accurate with satisfactory results. The SIA method is found to be accurate when the results are statistically compared with the results obtained by the standard method.