Portable Quantitative Chemical Analysis: Digital Image Colorimetric Detection of Fe(III) with Curcumin Paper

Hands-on experiences in analytical chemistry laboratories are essential to improve students’ technical skills on handling analytical glassware and instruments, but the coronavirus pandemic in 2020–2021 disrupted such learning activities. Thus, alternative remote activities are required to supplement practical skills. In this work, a new portable experiment to determine the concentration of Fe(III) by digital image colorimetry with curcumin paper is described. This experiment utilized complexation between Fe(III) and curcumin on a paper substrate, which changed from yellow to red-orange. Then, the RGB intensity changes, obtained using smartphones/devices, were plotted against the Fe(III) standard concentration to construct an external standard calibration curve for determining Fe(III) in unknown solutions. Using students’ own smartphone/device enhanced their interest, and the portable small-scale experiment kit enabled a remote hands-on experience at their residence (Lab@Home). The experiment had been implemented both in Lab@Home and in-person formats for three semesters with 591 second-year students majoring in chemistry and other sciences, showing a satisfactory self-evaluated outcome (4.27 from 5) and post-test score (81.5%). The proposed experiment is a showcase to introduce modern analytical chemistry through smartphone/device and digital image colorimetry, while enhancing students’ skills and interests in analytical chemistry laboratory.