Smartphone-based digital image colorimetry for determination of iron in cereals and crispy seaweed using Terminalia...

In this research, a novel sample pretreatment of whole wheat bread, granola, and crispy seaweed samples was developed for iron(III) determination by digital image colorimetry. The developed method was compared with UV-visible spectrophotometry. The procedure involved weighing the sample (∼0.1 g) and mixing it with a mixture of concentrated nitric acid (65%) and hydrogen peroxide (30%) (2 : 1 v/v). Then, the mixture was irradiated with UV light until it became dry. The residue was then dissolved in deionized water. The sample solution was diluted with deionized water before forming a complex with Terminalia chebula Retz. extract in acetate buffer. Under the optimal conditions, the color of the complexes was violet. When analyzed with an inhouse developed smartphone-based digital image colorimeter, the linear range was 1.0-6.0 mg L^-1 with a correlation coefficient of >0.993. The percentage recoveries were in the range of 84.8-90.2. The limit of detection (LOD) and the limit of quantification (LOQ) were 1.06 and 3.55 mg L^-1, respectively. From the results, it can be concluded that the developed method is accurate, simple, cost-effective, and environmentally friendly. The statistical paired t-test proved that there was no significant difference in the results when compared with a UV-visible microplate reader using gallic acid as the color forming reagent and a flame atomic absorption spectrophotometer as a reference instrument at 95% confidence level.