Low-Cost Method for Quantifying Sodium in Coconut Water and Seawater for the Undergraduate Analytical Chemistry Laboratory: Flame Test, a Mobile Phone Camera, and Image Processing

The flame test is a classical analytical method that is often used to teach students how to identify specific metals. However, some universities in developing countries have difficulties acquiring the sophisticated instrumentation needed to demonstrate how to identify and quantify metals. In this context, a method was developed based on the flame test to quantify sodium in coconut water and seawater using recorded videos of a flame during the experiment and subsequent image treatments with an R statistics platform. This experiment provided undergraduate students an opportunity to study important topics such as atomic theory, emission spectroscopy, quantitative analysis, and image processing. Finally, students measured the sodium content in seawater collected from a region of the Rio Grande do Norte coast, an important region for manufacturing salt. They obtained sodium concentrations that ranged from 11.2 to 12.2 g dm–3 and calibration curves that presented good linearity (R2 > 0.91). The sodium content of coconut water determined was 48 ± 4 mg dm–3. The results demonstrate an interesting and simple method that can easily be applied in experimental Analytical Chemistry courses, and this experiment would also be appropriate for pre-college students.