Sample preparation techniques for the determination of short-chain organic acids in coffee samples by the automated solid-phase extractor
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Abstract
The objective of this research was to study sample preparation techniques for reducing interference before analyzing six types of short-chain organic acids: acetic acid, propionic acid, isobutyric acid, butyric acid, isovaleric acid, and valeric acid, using gas chromatography (GC) from coffee samples brewed with a moka pot. The sample preparation used a fivefold dilution of the sample with methanol and deionized (DI) water, then separated the larger particles using a centrifuge, and cleaned the sample using an automated solid-phase extractor with Sep-ed C18 cartridges at a loading rate of 0.1 mL/min and sample volume of 5 mL. The results from the study of the physical characteristics of the samples before and after preparation showed a reduction in particle size from 6.78±4.69 μm to 1.40±0.74 μm. The values for red color intensity, yellow color intensity, and yellowness index decreased, while brightness and whiteness index increased significantly with a statistical significance at P < 0.05. The method’s usability yields an adequately broad analytical range, with a linear correlation coefficient (r) > 0.9997. The detection limit was in the range of 2.5-10 mg/L, and the quantification limit was in the range of 5-20 mg/L. The recovery rate ranged from 93.8±3.6% to 104.3±1.8% and the reproducibility was in the range of 1.6-4.7%, which was acceptable. Furthermore, the qualitative analysis using GC-MS identified the area under the graph ranging from 36.4% to 50.4% and the quantitative analysis, calculated per coffee bean weight, using of GC-FID revealed that the total content of organic acids to be in the range of 3.08-7.92 g/kg.
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