Supercritical fluid extraction of 4(5)-methylimidazole (4MeI) and 2-acetyl-4(5)-(1,2,3,4)tetrahydrohydroxybutylimidazole (THI) from grounded coffee with liquid chromatographic - electrospray mass spectrometric (HPLC/ESI-MS) quantification
Résumé
Two polar analytes, 4(5)-methylimidazole (4MeI) and 2-acetyl-4(5)-(1,2,3,4-tetrahydroxybutyl)-imidazole (THI) were extracted with supercritical CO2 modified with an aqueous methanol. The method was applied to a roasted coffee powder with good recoveries. Method efficiency was compared with that of solid phase extraction using SCX Disc cartridges and validated for spiked solid matrix. The analytes were determined using an isocratic high-performance liquid chromatography – mass spectrometry (HPLC/MS) on an Atlantis HILIC Silica column (150 x 2.1 mm, 3 mm) with 80 % methanol and 20 % 0.01 mol.l-1 ammonium formate as a mobile phase. The lower limit of quantification was 1.46 pg for 4MeI and 2.11 pg for THI. The linearity of the calibration curves was satisfactory as indicated by correlation coefficients of > 0.999. The coefficient of variation for the intra-day and the inter-day precision was < 4% (n = 6). The accuracy was in the range 98 % - 101%. Recovery was ≥ 98% and ≥ 99% for THI and 4MeI, respectively. Several varieties of coffee and consumer mixtures were analyzed to test the method.
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