Validation of a spectrophotometric method for the determination of iron (III) impurities in dosage forms

A spectrophotometric method (lambda=535 nm) for the iron (III) impurities determination in iron protein-succinylate complex syrup using thioglycolic acid in basic ambient was proposed and validated. Assay samples were treated with 0.1 N hydrochloric acid and centrifuged to remove the interfering active drug. Linear response (r=0.9999) was observed over the range of 0.005-0.2% of the iron (III) with respect to the complex nominal concentration. The accuracy could be considered very satisfactory (recovery=97-99%). The intra-day precision (RSD) of impurity amongst six independent sample preparations, was 1.4%, and there was no significant difference between intra- and inter-day studies. Intermediate precision indicated that the assay possessed high degrees of ruggedness. The limit of quantitation was 0.005% of impurity with respect to the active drug. The results obtained for iron (III) were compared statistically with those obtained with the standard addition method by means of the Student's t-test and the variance ratio F-test; no significative difference was found.