Digital image determination of copper in food and water after preconcentration and magnetic tip separation for in-cavity desorption/color development.

A new analytical method for measuring copper in food and water was developed and validated, employing a solid-phase extraction (SPE) technique combined with digital-image-based (DIB) detection. A novel magnetic adsorbent of zinc ferrite/Citrullus colocynthis biochar (ZF@C.BC) was used to preconcentrate copper. A magnetic tip was used to separate the copper-loaded adsorbent from the extraction medium and to dispense it to the DIB plate. In-situ desorption and development of the spot color with iodide-starch reagent were carried out, and a digital image of the developed spots was captured using a smartphone and processed using ImageJ software. The copper adsorption capacity was 91.3 mg g-1. Desorption was effected using a 0.3 mol L-1 hydrochloric acid. The preconcentration factor was 300, the limit of detection was 4.8 µg L-1, the linearity was 16-600 µg L-1 and the sample throughput was 12 h-1. The developed approach was validated by analyzing food and water samples, confirming recoveries ≥ 91 % and 88 %, respectively, with RSD ≤ 8.4 %, n = 3.

Analysis of total phenolic compounds in tea and fruits using diazotized aminobenzenes colorimetric spots.

The present work describes a novel and rapid approach for evaluating total phenolic compounds (TPCs) in tea and fruits using colorimetric spots and the digital image-based (DIB) method. Colorimetric spots were formed by reacting diazotized aminobenzenes namely sulfanilic acid, sulfanilamide, or aniline with TPCs in the extract to form an azo dye. The limit of detection (LOD) was 6.5, 5.5, or 5.1 mg GAE (gallic acid equivalent) L-1 and the analytical range was 25-500, 20-500, or 18-200 mg GAE L-1, respectively. Correlation with the Folin-Ciocalteu assay was significant (Pearson coefficient, R = 0.970-0.991) while the antioxidant activity assay was moderate to high (R = 0.737-0.977). The method developed was successfully applied to the analysis of tea and fruits and showed RSD (n = 3) not exceeding 9.6, 8.5, and 9.7%, respectively. Ecologically, the DIB method developed could determine the variation of TPCs within cultivars and was found to be strongly dependent on the growing environment.