Possibilities of Mass Spectrometry and Tandem-Mass Spectrometry in the Analysis of Cellulose Ethers

The investigation of the substituent pattern of cellulose and starch ethers and esters on various structural levels as in the glucosyl unit, along the polymer chain, and over the polymer molecules, still is a very challenging task. By means of mass spectrometric methods as ESI-MS or MALDI-TOF-MS the composition of oligosaccharide mixtures which represent the substituent distribution in the original polymer can principally be determined. However, to obtain reliable quantitative data mass spectra must be recorded under appropriate instrumental conditions and after special sample preparation While O-methyl/O-methyl-d₃-oligosaccharides give representative data with the mentioned MS techniques and FAB-MS as well, hydroxyalkyl ethers require labelling with a quaternary ammonium tag and MALDI-TOF-MS to prevent discrimination of lower substituted oligosaccharides. In this way, information on the neighbourhood of glucosyl units in the polymer chain is available which – together with the monomer composition – is a valuable parameter to describe a random or a heterogeneous pattern with regions of local higher densities of substituents compared to the random model, a regular distribution, or a block-like substituent pattern, i.e. a more clustered localisation of substiuents in the polymer chain. In addition, tandem-mass spectrometry (ESI-MSⁿ) allows to gain further insight in the composition of isomeric oligosaccharide derivatives of the same m/z ratio and to calculate the complete monomer composition of methyl celluloses.