Determination of neutral and acidic sugars in soil by capillary gas-liquid chromatography after trifluoroacetic acid hydrolysis

A new method for the simultaneous, quantitative determination of neutral and acidic sugars liberated from non-cellulosic soil carbohydrates is described. A single hydrolytic step with 4 M trifluoroacetic acid (TFA) at 105°C for 4 h is suggested to be more effective in releasing sugar monomers from soil than other recommended hydrolysis procedures (2.5 M H2SO4 reflux for 20 min followed by 12 M H2SO4 for total sugar hydrolysis; 1 M HCl for 5 h at 105°C or for 7 h at 100°C; 4 M TFA at 125°C for 1 h or 2 M TFA at 105°C for 2 h). Different materials were tested for purification (cation exchange resin, activated carbon, C-18, XAD-4, XAD-7), and the combination of the cation exchange resin and of XAD-7 is recommended. Analysis of purified monomers involved separation of O-methyl-oxime-trimethylsilyl derivatives by capillary gas-liquid chromatography in 21 min. Results were compared with those obtained from spiked soil samples, resulting in a high recovery of standard mixtures (70–109% for individual sugars) processed in the way proposed here. The method was sensitive and characterized by simple, accurate and rapid work-up and, therefore, is suitable for routine use.