Stock solutions of HMF (1000 mg L1) were prepared in ultrapure water daily and stored at 7 C, protected from light. The standard solutions were prepared in the concentration range of 1.05.0 mgL1byadequatedilutionfromthestocksolution.Tests were performed previously to check the HMF range in the samples. Thus different ratios of mass and volume in the sample solution preparation were used (S1–S6 samples, 0.5 g in 250 mL and for CS1–CS6 samples, masses between 0.5 and 3.0 g in 100 mL), ensuring that the concentration of these stayed within of analytical curve (1.05.0 mgL1).