Microdetermination of L-ascorbic acid in pharmaceutical preparations by iodide ion-selective electrode and spectrophotometry

Two methods for determining low levels of L-ascorbic acid in pharmaceutical preparations are described. The potentiometric method is based on oxidation of an aqueous ascorbic acid solution with iodine in chloroform. The iodide ions produced in the aqueous phase are determined with the iodide ion-selective electrode using a standard calibration graph technique. The spectrophotometric method is based on oxidation of ascorbic acid with iron(III). The equivalent amount of iron(II) produced is determined as iron(II)-2,4,6-tri(2-pyridyl)-triazine chelate at 595 nm. The results show a mean recovery of 100.067±0.1435 for the potentiometric method, 100.267±0.32 for the spectrophotometric method.