Summarizing shortly the methods described above, it can be stated that the choice of analytical methods in general depends on sample characteristics, matrix complexity, the aim of the analysis, accessible equipment and the amount of resources available.

For instance in order to be analyzed by GC, compounds in the samples must be able to get volatilized and additionally possess thermostability.

In case of LC, solubility in the mobile phase is important as well as size, structure and hydrophobicity, presence of functional groups, etc.

Regarding matrix complexity it could be also mentioned that chroma­tography can be used both for the separation of a compound from the matrix and for quantification and identification. It is important but rarely considered that no residual matter should remain in the samples; especial­ly heavy compounds, which are difficult to evaporate in the GC columns, could significantly influence subsequent analyses. Thus, regular control of retention times and response factors, as well as column cleaning or re­placement in due time should not be overlooked. For some samples related to the analysis of biomass even prefractionation could be necessary.

FIGURE 11: Typical gas chromatogram showing the major sugar units released upon methanolysis of a sample (spruce wood) containing hemicelluloses (Std = internal standard, sorbitol)

FIGURE 12: Equilibrium of different forms of sugars