Kinetic determination of vitamin B12 in pharmaceuticals by the continuous addition of reagent technique.

An automatic kinetic method for the determination of micro amounts of vitamin B12 in pharmaceutical samples based on the fast formation of a coloured complex between the cobalt contained by this vitamin and PAR [4-(2-pyridilazo)resorcinol] in a weakly alkaline medium and on the use of the continuous addition of reagent technique for the mixing of sample and reagent is reported. The reaction is monitored by measuring the changes in the absorbance at 510 nm characteristic of the complex formed. The linear range of the determination is 1.1-34.5 micrograms ml-1 and the relative standard deviation is 1.2%. The sample throughput is 75 h-1 (triplicate runs). The results obtained in analyses of pharmaceutical samples showed excellent correlation with nominal contents and the results of atomic absorption spectrophotometric analyses.