FLOW-INJECTION COLORIMETRIC METHOD FOR THE ASSAY OF VITAMIN-C IN DRUGFORMULATIONS USING TRIS,1-10-PHENANTHROLINE IRON(III) COMPLEX AS AN OXIDANT IN SULFURIC-ACID MEDIA

A simple, fast and accurate colorimetric flow injection (FI) method su itable for the assay of vitamin C in drug formulations was proposed. I n the method, vitamin C was injected into a flowing stream of iron(III ) and then mixed with 1,10-phenanthroline in 0.05M sulphuric acid medi a. The mixture was allowed to react in a 45-cm long coil and the resul ting solution of tris, 1-10-phenanthroline-iron(II) complex was monito red at 510 nm. The method was adopted by fully investigating the kinet ics of the reaction and proposing a suitable mechanism. A throughput o f 100 samples per hour was achieved with a relative standard deviation of 0.88% for vitamin C concentration range of 100-400 ppm.