Abstract

The aim of this investigation was to develop a spectrophotometric method in the visible range for quantitative determination of Fe³⁺ in a pharmaceutical formulation based on complexation with methylthymol blue. The reaction occurred at a temperature of 30° and the absorbance remains constant after 25-30 min; the blue-colored resulting complex had a maximum absorption at 628 nm. The combination ratio was established through the Job’s method of continuous variations. In acetate buffer (pH=5), Fe³⁺ forms a complex of 1:1 with methylthymol blue. Lambert-Beer law was obeyed to the concentration area of (2-6) µg/ml; the calibration curve is described by the regression line A= 0.1025° (µg/ml) -0.0013 with a correlation coefficient of R²= 0.9997. For the validation of the method the following parameters were studied, linearity, accuracy, limit of detection, limit of quantification and retrieval. Confidence interval of the average retrieval ranged from 98.79 to 101.13 %. The non-interference of excipients in the solution makes the method suitable for routine dosage of iron in polymaltose complexes. This visible spectrophotometric method was applied to determine Fe³⁺ concentration in polymaltose iron complex. The validation parameters confirmed that this method could serve to determine Fe³⁺.