Determination of niacin and niacinamide in pharmaceutical products by automatic discrete-sample analysis

A spectrophotometric method is proposed for the determination of small amounts of iodide. The method is based on the reduction of bis(neocuproine)-coppcr(II) to the monovalent copper chelate cation in the aqueous phase by iodide ion and subsequent solvent extraction into chlorobenzene of the ion-pair formed between bis(neocuproine)copper(I) cation and the tri-iodide anion. At least a 5-fold molar amount of the copper(II) chelate cation, relative to iodide, is needed, and the optimal pH range is 3–5. The absorbance of the extract at 370 nm is a linear function of iodide concentration in the aqueous phase over the range 5·lO^-6–4·10^-5M (ca. 0.6–5 p.p.m.). The relative standard deviation was 1.0%. Large amounts of fluoride and chloride (2000-fold molar) and bromide (50-fold) did not appreciably affect the determination of iodide. The extraction mechanism is elucidated.