MECHANISTIC STUDY AND KINETIC DETERMINATION OF VITAMIN-C EMPLOYING THE SEQUENTIAL INJECTION TECHNIQUE

For the first time, the robust sequential injection (SI) technique has been employed for full kinetic investigation of the oxidation reactio n of vitamin C. Iron(III) in sulphuric acid media was used as an oxida nt and 1,10-phenanthroline as an indicator and the resulting solution of tris 1,10-phenanthroline-iron(II) complex was monitored spectrophot ometrically at 510 nm. The reaction orders with respect to each reagen t were determined by the SI-technique and were found to be 1, 1, and - 1 for vitamin C, iron(III) and hydrogen ions respectively. On the basi s of these values a rare law was developed and a plausible mechanism w as established. A kinetic method for the analysis of vitamin C in drug formulations based on the results obtained above was thus validated. The drug in the range 20-300 ppm was determined by the kinetic method using 1.6 x 10(-3) mol dm(-3) ammonium ferric sulphate in 0.02 mol dm( -3) sulphuric acid with the aspiration volume of 944 mu l and the fixe d-time of 180 s. The results thus obtained by the SI-kinetic method we re statistically compared with those obtained by the British Pharmacoe bia standard method and found to be accurate, precise and fast. (C) 19 98 Elsevier Science B.V.