Determination of total acid content in biomass hydrolysates by solvent-assisted and reaction based headspace gas chromatography

This work reports on a novel method for the determination of total acid (TA) in biomass hydrolysates by a solvent-assisted and reaction-based headspace gas chromatography (HS-GC). The neutralization reaction between the acids in hydrolysates and bicarbonate in an ethanol (50%) aqueous solution was performed in a closed headspace sample vial, from which the carbon dioxide generated from the reaction was detected by HS-GC. It was found that the addition of ethanol can effectively eliminate the precipitation of some organic acids in the biomass hydrolysates. The results showed that the reaction and headspace equilibration can be achieved within 45   min at 70   °C; the method has a good precision (RSD   <   3.27%) and accuracy (recovery of 97.4–105%); the limit of quantification is 1.36   μmol. The present method is quite suitable to batch analysis of TA content in hydrolysate for the biorefinery related research.