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چکیده
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The application of layered double hydroxide–Al2O3–polymer mixed‐matrix disks for solid‐phase extraction is reported for the first time. Al2O3 is embedded in a polymer matrix followed by an in situ metal‐exchange process to obtain a layered double hydroxide–Al2O3–polymer mixed‐matrix disk with excellent flow‐through properties. The extraction performance of the prepared disks is evaluated as a proof of concept for the automated extraction using sequential injection analysis of organic acids (p‐hydroxybenzoic acid, 3,4‐dihydroxybenzoic acid, gallic acid) following an anion‐exchange mechanism. After the solid‐phase extraction, phenolic acids were quantified by reversed‐phase high‐performance liquid chromatography with diode‐array detection using a core–shell silica–C18 stationary phase and isocratic elution (acetonitrile/0.5% acetic acid in pure water, 5:95, v/v). High sensitivity and reproducibility were obtained with limits of detection in the range of 0.12–0.25 μg/L (sample volume, 4 mL), and relative standard deviations between 2.9 and 3.4% (10 μg/L, n = 6). Enrichment factors of 34–39 were obtained. Layered double hydroxide–Al2O3–polymer mixed‐matrix disks had an average lifetime of 50 extractions. Analyte recoveries ranged from 93 to 96% for grape juice and nonalcoholic beer samples.
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