The present work describes a simple hands-on experiment kit for colorimetric quantification of ferric (III) ion (Fe 3+ ) in an aqueous medium using anthocyanin extracted from Ruellia tuberosa L. as a green indicator. The extraction of a high amount of anthocyanin was easily accomplished by using only hot water instead of an organic solvent. The formation of the colored Fe 3+ −anthocyanin complex occurred on a homemade 24-well plate and the generated color was captured by a smartphone. The increase in color intensity was measured in the red, green, blue (RGB) system by the ImageJ software under the optimum conditions. The developed method enabled quantification of Fe 3+ at low concentrations with the detection limit of 0.03 mg L −1 and provided the linear range (0.05−2.0 mg L −1 ) with good linearity (R 2 = 0.9985) with Fe 3+ concentration. The concentrations of Fe 3+ in water samples determined by the developed method were not significantly different from those measured with UV−visible spectrophotometry at a 95% confidence level. In addition, the extracted anthocyanin stored at 4 °C was stable for two months. This hands-on experiment was implemented as a 2 h activity for 30 grade-12 students in which they were asked to determine the concentration of Fe 3+ in a water sample using the smartphone-assisted colorimetric 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.
We successfully developed a fluorometric paper-based
test kit for
the selective and sensitive determination of cyanide using nitrogen-doped
graphene quantum dots (N-GQDs) as the fluorescent probe. Citric acid
and tris(hydroxymethyl)aminomethane were precursors for the one-step
synthesis of N-GQDs via in situ hydrothermal methods,
providing a high quantum yield of 57.9%. The proposed mechanism uses
a fluorescence turn-on approach. Specifically, the fluorescence of
N-GQDs is quenched by the incorporation of Ag+ via a photoinduced
electron transfer (PET). During the detection step, sulfuric acid
converts cyanide (CN–) into hydrogen cyanide (HCN).
The Ag+ species on the N-GQD surface then react with the
evolved HCN via a coordination bond to form a silver cyanide complex,
resulting in the fluorescence emission of the N-GQDs being turned
back on. As a result, the fluorescence emission intensity of N-GQDs
linearly increased with increasing CN– concentrations
in the range of 0.5–25 mg L–1, with a limit
of detection (LOD) of 0.08 mg L–1. Notably, the
developed sensor has advantages in terms of simplicity, rapidity,
low cost, and high selectivity toward CN–. The analytical
performance of the test kit was also validated the performance of
the test kit against a conventional precipitation titration method.
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