Carbohydrates charge requirements

The total alkaline charge required for xylan extraction was of major importance for the feasibility of the isolation process. These factors were dependant on the alkalinity of the extraction liquor and the consistency used in the process. In Figure 1 the effect of alkalinity on the yield of xylan and extraction residue is depicted for 10% and 25% consistency. The upper picture for 10% consistency demonstrates that an increase of NaOH concentration from 2.2 to 5% resulted in a continuous increase of xylan yield. Totalling the yield of xylan and residue it became apparent that up to 20% of the starting materials were not recovered. This material remained in the precipitation liquid and should consist of extractives, lignin fragmentation products, and low molar mass carbohydrates. A further analysis of those components was not pursued at this stage of the project. 

Carbohydrates are very difficult compounds to analyze using CE because of their inherent structural complexity, frequent lack of a charge and lack of a UV or fluorescent chromophore. They thus require derivatization to facilitate ion formation and detection. 

In general, any satisfactory theoretical calculation of a nuclear coupling constant requires reliable calculation of the molecular wavefunction. As a consequence, a realistic approximation to the actual charge distribution in the carbohydrate molecule must presumably enter any theoretical model that attempts to provide a quantitative interpretation of solvent effects. The simplest treatments, and those that have been proposed most frequently to account for the solvent effect in the absence of specific effects, are those in which the solvent is treated as a continuum surrounding the solute molecule. Several different models where the solvent dependence of coupling interactions is related to the polarity of the medium have been proposed.78-79 The solvation theory80,81 has been successfully used within the FPT formalism to interpret the effect of solvent on Jc H and 3/CH. On the basis of this model, the Hamiltonian of a particular molecule includes the solvent-solute interaction term //so,v ... 

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