Digital-image eco-friendly spot test with liquid–liquid microextraction for selective determination of flavonols in berries

• Published in: Microchemical journal 2023-10, Vol.193, p.109207, Article 109207
• Main Authors: Claudio Martins, Luís, Soares, Samara, Rocha, Fábio R.P.
• Format: Article
• Language: English
• Subjects: Berries; Digital-image photometry; Green analytical chemistry; In situ analysis; Microanalysis
• ISSN: 0026-265X; 1095-9149
• DOI: 10.1016/j.microc.2023.109207

[Display omitted] •A novel approach for fast, cost-effective, and selective determination of flavonols;•Combination of salt-assisted liquid–liquid microextraction and digital-image photometry;•Environmental friendly sample preparation using ethanol and fresh samples;•Practical and selective strategy to separate anthocyanin from flavonols. Spots tests are attractive for food control due to the potential for in situ analysis, quick achievement of results and environmental friendliness. Flavonols, a class of natural compounds with many benefits to human health, are commonly determined by spectrophotometry and chromatography, often generating large amounts of harmful wastes. Besides, the spectrophotometric methods are typically not selective, with interferences from anthocyanins and phenolic acids. To circumvent these drawbacks, this work proposes a cost-effective and environmental friendly spot test associated with liquid–liquid microextraction for determination of flavonols in berries by digital-image photometry. Flavonols were extracted from berries with ethanol and further separated from anthocyanins by ethyl acetate salt-assisted microextraction. After formation of colored Al(III)-flavonol complexes, digital images were obtained in a porcelain plate using a smartphone camera. The RGB values were extracted using ImageJ® software, and channel B was taken for photometric measurements. A linear response was achieved within 0.33–5.00 mg/L (1–17 µmol/L) quercetin equivalent concentration (QE) with r ≥ 0.997. The coefficient of variation (n = 10) and limit of detection were estimated at 3.9% and 0.1 mg/L QE (0.3 µmol/L), respectively. The accuracy was assessed by comparison to the spectrophotometric procedure, with results in agreement at the 95% confidence level. The proposed procedure minimized reagent/solvent consumption (70 µg of Al(III), 142 mg of Na2SO4, equivalent to 9.2 µL of HCl, and 2.0 mL of ethyl acetate) and the waste generated is mostly composed by water and ethanol.