Hydroxyethylmethyl celluloses (HEMC, DS(Me) 1.46-1.66, DS(HE) = 0.14-0.17) have been analyzed with respect to their methyl and hydroxyethyl pattern in the glucosyl units and along the polymer chain. Methyl groups were located by GLC/MS after direct hydrolysis, reduction, and acetylation, and the distribution of hydroxyethyl residues in the glucosyl units could be determined with enhanced sensitivity after permethylation to unify a certain HE pattern occurring in combination with various methyl patterns in a single peak. To get insight into the distribution of Me and HE along the cellulose chain, a method was developed which overcomes the strong discrimination of relative ion intensities caused by hydroxyalkyl groups and enables quantitative determination of the oligomer composition after random degradation for the first time. This comprises perdeuteriomethylation; partial acid hydrolysis; reductive amination with propylamine; and, finally, permethylation to yield completely O- and N-alkylated, permanently charged oligosaccharides. Although the methyl pattern can be determined by electrospray ionization ion-trap mass spectrometry (ESI-IT-MS) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), as well, only MALDI-TOF-MS produced representative data for a quantitative evaluation of the HE pattern. Distribution of HE groups matches with a random distribution calculated from the monomer composition, whereas the methyl pattern was heterogeneous to a different extent.

Three hydroxypropylmethyl celluloses (HPMC 1, 2, 3; DS Me =2.06, 1.99, 2.04; MS HP =0.21, 0.19, 0.21) have been analyzed with respect to their methyl and hydroxypropyl pattern in the glucosyl units and along the polymer chain. The determination of the methyl pattern in the glycosyl unit was performed by GLC/MS after hydrolysis, reduction, and acetylation, while the distribution of hydroxypropyl residues in the monomers could be analyzed with higher sensitivity including a permethylation step prior to hydrolysis. To determine the distribution of the substituents along the polymer chain, a method developed for hydroxyethylmethyl cellulose (HEMC) was applied. This method comprises random partial acid hydrolysis after perdeuteromethylation and reductive amination with propylamine, followed by N-and O-alkylation, yielding completely alkylated and permanently charged oligosaccharide derivatives. These compounds could be quantitatively analyzed by means of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), since all discrimination effects related to the hydroxyalkyl groups are leveled off by the sample preparation procedure in combination with the choice of a MALDI-TOF instrument. Methyl data deviate to some extent from the random distribution calculated from the monomer composition, but in contrast to methyl cellulose (MC) or HEMC, it is not heterogeneous, but more regular. The distribution of HP groups is random within experimental error as has been found for HEMC as well.

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Three HECs with a high MS (HEC 1: 1.89, HEC 2: 1.94, HEC 3: 3.03) were analyzed with respect to their substituent distribution and tandem reaction in the glucosyl unit by GLC of the corresponding glucitol acetates, and along the polymer chain by MALDI-ToF-MS after a multi-step sample preparation. For comparison of the experimental data with a random pattern an extended Bernoulli plot was applied to calculate a random distribution for the composition of un-, mono-, di-, tri-, and up to heptasubstituted glucosyl units (c0, c1, c2, ... c7).