Determination of Calcium in Dietary Supplements: Statistical Comparison of Methods in the Analytical Laboratory

A laboratory experiment is described in which students compare two methods for the determination of the calcium content of commercial dietary supplement tablets. In a two-week sequence, the sample tablets are first analyzed via complexometric titration with ethylenediaminetetraacetic acid and then, following ion exchange of the calcium ion present for hydronium ion, by acid base titration with sodium hydroxide. Upon completion of the laboratory work, students pool their data with classmates and perform a statistical analysis to determine whether the average values of the calcium content obtained by the two methods are equivalent. When taken together with such considerations as analysis time, accuracy, simplicity and ease of use, susceptibility to interference, and waste generation, these results enable the students to evaluate the relative merit of the two approaches to calcium determination. In so doing, they are introduced to an important aspect of "real-world" chemical analysis, namely, selection of the method best suited for the determination of a particular analyte in a given sample.