It depends from the complexity of the starting biomass...however NREL standard method [A. Sluiter, B. Hames, R. Ruiz, C. Scarlata, J. Sluiter, D. Templeton, D. Crocker, Determination of structural carbohydrates and lignin in biomass, Laboratory Analytical Procedure (LAP) NREL/TP-510-42618, 2008a] is reliable and can be adapted to different biomass feedstocks...analysis of carbohydrates is performed by HPLC.
for paper samples TAPPI methods are generally used but also NREL methods give reasonable results.