Microliter-Scale Colorimetry Using a Low-Cost Digital Microscope for the Determination of Phosphorus and Iron
DOI:
https://doi.org/10.57260/stc.2026.1816Keywords:
Digital microscope, Digital image colorimetry, Phosphorus, Iron, Green analytical chemistryAbstract
Quantitative analysis using standard methods requires expensive instruments and large amounts of chemical reagents, which can be a limitation for organizations with restricted budgets. This study aimed to develop a microliter-scale colorimetric method using an economical digital microscope for the determination of total phosphorus in soil and total iron in steel office materials, and to evaluate the method performance against reference methods. The developed method was based on RGB color measurement of reaction droplets placed on a white acrylic plate using the Just Color Picker software. Phosphate was determined using the molybdenum blue reaction, while iron was determined using the 1,10-phenanthroline reaction. The investigated conditions included the color channel used for measurement, reaction time, and the volume ratio of reagents to sample solution. The optimum conditions for phosphate determination were the R color channel, a reaction time of 180 s, and a total volume of 60 µL, whereas those for iron determination were the B color channel, a reaction time of 5 min, and a total volume of 30 µL. The developed method exhibited linear ranges of 0.5–18 mg L-1 (R² = 0.9887) for phosphate and 3–20 mg L-1 (R² = 0.9966) for iron, with limits of detection of 0.30 and 0.19 mg L-1 and %RSD values of 1.59 and 0.24%, respectively. The results obtained for five soil samples and three types of office materials were in good agreement with those obtained by ultraviolet–visible spectrophotometry, with mean relative percent differences (%RPD) of 8.90% and 1.80%, respectively. The percentage recoveries of iron ranged from 94.40% to 102%. The developed method requires only microliter-scale volumes of reagents and employs a single device for the determination of both analytes. Therefore, it has potential as a preliminary screening method for agricultural extension work and analytical chemistry education in educational institutions with limited budgets.
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