The analysis of HMF was carried out according to our previously established method [25 (link),26 (link)], with minor modifications. For a sample of 1 g of FDT powder in plastic centrifuge tubes, 8 mL of deionized water and 0.5 mL of Carrez I and II solutions were added. The mixtures were vortexed for 3 min and then shaken for 30 min at 40 °C, subsequently, centrifuged at 5000× g for 10 min, to obtain clear supernatants. The HMF in supernatants was purified by applying the Waters Oasis HLB SPE cartridges (200 mg, 30 μm). The prepared samples were filtered by a 0.22 μm nylon filter, and then analyzed with HPLC.
Instrumental analysis was performed using a Shimadzu HPLC system (Shimadzu, Kyoto, Japan) consisting of a CBM-20A system controller, two LC-20AT pumps, a DGU-20A degasser, an LC-20A UV detector, and a CTO-20AT column oven. The analysis system was equipped with a Thermal ODS C18 analysis column (4.6 mm × 250 mm, 5 μm). The temperature of the column oven was set to 35 °C. The UV detection wavelengths was 284 nm. The mobile phase was acetonitrile:water (5:95, v/v) at a flow rate of 0.6 mL·min−1, and the run time was 20 min per sample. The injection volume was 20 μL. LOD and LOQ of the samples were 0.06 mg·kg−1 and 0.15 mg·kg−1, respectively.
Instrumental analysis was performed using a Shimadzu HPLC system (Shimadzu, Kyoto, Japan) consisting of a CBM-20A system controller, two LC-20AT pumps, a DGU-20A degasser, an LC-20A UV detector, and a CTO-20AT column oven. The analysis system was equipped with a Thermal ODS C18 analysis column (4.6 mm × 250 mm, 5 μm). The temperature of the column oven was set to 35 °C. The UV detection wavelengths was 284 nm. The mobile phase was acetonitrile:water (5:95, v/v) at a flow rate of 0.6 mL·min−1, and the run time was 20 min per sample. The injection volume was 20 μL. LOD and LOQ of the samples were 0.06 mg·kg−1 and 0.15 mg·kg−1, respectively.
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