Analysis of technical lignins by two- and three-dimensional NMR spectroscopy

Tiina M. Liitiä, Sirkka L. Maunu, Bo Hortling, Merja Toikka, Ilkka Kilpeläinen (Corresponding Author)

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Abstract

Modern multidimensional NMR spectroscopic methods were applied to investigate the effects of kraft pulping and oxygen delignification on lignin side-chain structures. In addition to the two-dimensional HSQC measurements, the three-dimensional HSQC-TOCSY technique was utilized to elucidate the 1H-1H and 1H-13C correlations of individual spin systems and thus indicate a certain lignin sidechain structure. Unlike earlier, nonlabeled samples were used for 3D measurements. According to 2D and 3D NMR spectra, most of the structures identified in milled wood lignin (MWL) are still present in technical lignins after kraft pulping and oxygen delignification. Although the main reaction during kraft pulping is the cleavage of β-O-4 linkages, these structures are still left in spent liquor lignin as well as in residual lignin. The amount of coniferyl alcohol and dihydroconiferyl alcohol end groups, as well as some unidentified saturated end groups, is higher in technical lignins than in MWL. Contrary to our earlier observations, no diphenylmethane structures were observed in any technical lignins. Vinyl aryl ether structures could not be detected in technical lignins either.

Original languageEnglish
Pages (from-to)2136-2143
Number of pages8
JournalJournal of Agricultural and Food Chemistry
Volume51
Issue number8
DOIs
Publication statusPublished - 9 Apr 2003
MoE publication typeNot Eligible

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Keywords

  • 3D HSQC-TOCSY
  • Kraft pulping
  • Lignin side-chain structure
  • NMR
  • Oxygen delignification
  • Residual lignin

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