Quantification of Iron(II) in Supplements Using Redox Titration and UV–Visible Spectroscopy

Abstract

This study examined a comprehensive approach to quantifying iron in over-the-counter supplements through two laboratory experiments designed for undergraduate students in analytical chemistry and instrumental analysis courses. The experiments employed redox titrations and UV–vis spectroscopy, reinforcing key techniques, such as titration, solution preparation, dilution, glassware handling, and spectroscopic analysis. In the first experiment, students prepared solutions and observed color changes, indicating the complete oxidation of iron II during redox titrations. In the second experiment, students utilized the Beer–Lambert law to construct and analyze an external calibration curve with a UV–vis spectrophotometer, enabling the measurement of iron levels in the supplements. The students performed a statistical analysis to discuss the mean and variance values between the two methods as well as compare their calculated iron amounts with the advertised quantity on product labels. The majority of students did not find a statistically significant difference in the average calculated iron content for the same analyzed brand between the two techniques. The average for the redox experiment was 67.20 ± 11.45 mg, while UV–vis was 63.83 ± 12.38 mg of iron. This experiment was designed to be adaptable and can include various over-the-counter products. Additionally, a method using a lower acid concentration was developed to minimize the use of concentrated acid. Although the experiments can be applied as individual experiments, the combination of both allowed students to reinforce key statistical techniques through a comparison of the two procedures. This comprehensive approach caters to students across different levels of chemistry courses, from introductory to advanced, providing a practical application of theoretical concepts.