Field and in-lab determination of Ca²⁺ in seawater

Portions of classic undergraduate quantitative analysis experiments in complexiometric titration and potentiometry are combined with a field-sampling experience to create a two period (2 × 3 h) comparison-based experiment for second-year students. A multifunctional chemical analysis device is used with calcium ion-selective electrode for field measurement of calcium concentration in seawater. The results are compared with later simultaneous potentiometric and colorimetric titration with ethylenediaminetetraacetic acid (EDTA). Students compare precision, difficulty, and sources of error of the different methods and present a written argument supporting their choice of best method including advantages and limitations. The experiment provides an introduction to chemistry in-the-field, sample collection and handling, complex matrices, imperfect methods, fallibility of instrumentation, real-world performance, and decision-making.