Smartphone-Assisted Colorimetric Determination of Iron Ions in Water by Using Anthocyanin from Ruellia tuberosa L. as a Green Indicator and Application for Hands-on Experiment Kit

The present work describes a simple hands-on experiment kit for colorimetric quantification of ferric (III) ion(Fe3+) in an aqueous medium using anthocyanin extracted fromRuellia tuberosaL. as a green indicator. The extraction of a highamount of anthocyanin was easily accomplished by using only hotwater instead of an organic solvent. The formation of the coloredFe3+-anthocyanin complex occurred on a homemade 24-well plateand the generated color was captured by a smartphone. Theincrease in color intensity was measured in the red, green, blue(RGB) system by the ImageJ software under the optimumconditions. The developed method enabled quantification of Fe3+at low concentrations with the detection limit of 0.03 mg L-1andprovided the linear range (0.05-2.0 mg L-1) with good linearity(R2= 0.9985) with Fe3+concentration. The concentrations of Fe3+in water samples determined by the developed method were notsignificantly different from those measured with UV-visible spectrophotometry at a 95% confidence level. In addition, the extractedanthocyanin stored at 4 degrees C was stable for two months. This hands-on experiment was implemented as a 2 h activity for 30 grade-12students in which they were asked to determine the concentration of Fe3+in a water sample using the smartphone-assistedcolorimetric method. The students'understanding of the related concepts of oxidation-reduction and determination of iron was collected by a diagnostic conceptual test. Having participated in the experiment, the students were found to have significantly improved understanding of both concepts