Complexometric Titration of Bismuth in Over-the-Counter Stomach Relief Products

Three direct complexometric titration methods for bismuth subsalicylate determination in over-the-counter stomach relief caplets and liquids are presented, as well as a UV–vis assay, for use in student laboratories. The main difference between titration methods is the choice of indicator; either xylenol orange (XO), pyrocatechol violet (PV), or potassium iodide (KI) is used. These methods are simple and safe, making this experiment desirable in a general chemistry or analytical laboratory to relate real-world sample analysis to theoretical titrimetric concepts. Learning outcomes, student feedback, and student data from Wichita State University (WSU) Chemistry II Honors lab, Bethel College Introduction to Chemistry lab, and University of Missouri (Mizzou) Quantitative Analysis lab are presented. The majority of students enjoyed this real-world sample analysis; however, titration results are more precise for more advanced students. The titration with EDTA using XO as an indicator is the method of choice for caplet analysis by the authors, but methods utilizing PV or KI as indicator are also acceptable, although the KI method may generate large amounts of iodide waste depending on class size. All titration methods presented are selective at low pH (∼1.5–1.6) and do not suffer interferences from commonly occurring ions such as magnesium and calcium. Using the titrimetric procedures presented in this work, all tested caplet and liquid brands appear to meet United States Pharmacopeia (USP) standards, where the allowable range of active ingredient is within 90–110% of label value.