One-pot iron determination in fortified flours using thymol-1,10-phenanthroline deep eutectic solvent and smartphone-based digital image photometry.

Iron fortification of flours is an important public health strategy for reducing iron-deficiency anemia. Conventional procedures for iron determination in fortified flours generally involve acid digestion followed by determination using either flame atomic absorption spectrometry or inductively coupled plasma optical emission spectrometry (ICP-OES), which require labor-intensive sample preparation, hazardous reagents, and costly instrumentation. An alternative analytical method, based on an extraction-complexation using a thymol-1,10-phenanthroline deep eutectic solvent (DES), is proposed to reduce costs, simplify the process, and minimize the number of analytical steps. The reaction was carried out in polypropylene microtubes, followed by stirring, centrifugation and measurement of the colored DES phase using a smartphone camera. The images were processed using the RGB color system, and channel B, corresponding to the complementary color of the formed complex, was selected as the analytical response. Under optimized conditions (50 µL aqueous Fe(II) solution or 50 mg flour, 100 µL DES, 200 µL of 2.5% (m/v) ascorbic acid, and 5 min of reaction under agitation). A linear response was obtained for Fe concentrations ranging from 1.5 to 20.0 mg L-1, corresponding to 9 to 120 mg kg-1 in flour, described by the equation S = (2.5 ± 0.1)C + (100 ± 1), with an R2 of 0.994, where S corresponds to the analytical signal defined as (255 - B). The limit of detection was 0.5 mg L-1 (3.0 mg kg-1), and the coefficient of variation was 1.4% (n = 10), indicating good precision of the proposed method. Results agreed with the reference procedures based on spectrophotometry and ICP-OES after extraction with diluted acid as evaluated by Bland-Altman analysis yelding mean biases of -0.52 mg kg-1 for spectrophotometry and 1.10 mg kg-1 for ICP-OES. Relative errors ranged, respectively, from -17.1% to 4.1% for spectrophotometry and from 0% to 18% for ICP-OES. The proposed method requires low sample amounts and reduces reagent consumption, resulting in minimal waste generation. Owing to its simplicity, cost-effectiveness, and alignment with green analytical chemistry, the proposed method represents a promising alternative for routine quality control of iron-fortified flours, and the application may be extended to other food matrices.