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Licensed Unlicensed Requires Authentication Published by De Gruyter November 30, 2011

Effect of pH on lignin analysis by Raman spectroscopy

Elina Warsta, Anni Lähdetie, Anna-Stiina Jääskeläinen and Tapani Vuorinen
From the journal


Ultraviolet resonance Raman (UVRR) spectroscopy is a powerful tool for structural lignin analysis in situ: modification or isolation of lignin from biomass is not necessary. UVRR spectroscopy is equally applicable for samples with high lignin content and those with very low lignin content. Monomeric phenolic lignin model compounds and wood pulp samples have been studied at neutral and alkaline pH with UVRR spectroscopy. Concentration of guaiacol correlated well with the relative Raman band intensity, which indicates that lignin-containing solutions can be quantitatively measured with UVRR spectroscopy. A change in pH induced a recordable shift in the aromatic band position in the spectra, which was 25–35 cm-1 with phenolic model compounds without para substitution, 8–12 cm-1 with phenolic model compounds with para substitution, and about 2–7 cm-1 with pulp samples. No shift was detected with a non-phenolic model compound. Increasing the amount of phenolic hydroxyl groups increased the UVRR band shift in pulp samples. Additionally, increasing the pH enhanced the relative aromatic band intensity in the UVRR spectra in solution of the phenolic model compound. Accordingly, pH adjustment is relevant prior to any lignin analysis with Raman spectroscopy.

Corresponding author. Aalto University, Department of Forest Products Technology, P.O. Box 16300, FI-00076 Aalto, Espoo, Finland

Received: 2011-8-17
Accepted: 2011-11-1
Published Online: 2011-11-30
Published in Print: 2012-05-01

©2012 by Walter de Gruyter Berlin Boston

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