Fig. 4

Chromatogram of hydrolysate 1, hydrolysate 2 and hydrolysate 3 analyzed with (a) the 50 mm guard column showing 5-HMF (peak 1) and furfural (peak 2) elution, and (b) 5-HMF and furfural concentrations of hydrolysate 1, hydrolysate 2 and hydrolysate 3 analyzed with the 50 mm guard column, 300 mm column and 30 mm guard column. HPLC parameters: column temperature 55 °C, mobile phase 5 mM sulfuric acid, flow rate 1.0 mL/min (0.6 mL/min for 300 mm column), refractive index detection