Determination of Eucalyptus spp lignin S/G ratio: A comparison between methods

The syringyl/guaiacyl ratio was determined for six different Eucalyptus spp. wood clones cultivated in four regions in Brazil. The determinants were made by pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) and the results were compared with those obtained by alkaline nitrobenzene oxidation method. The S/G ratios were obtained considering all the identified lignin derivatives in the pyrograms and also using two groups of markers. The first group of markers consisted of guaiacol, 4-methylguaiacol, 4-vinylguaiacol, trans-isoeugenol, syringol, 4-methylsyringol, 4-vinylsyringol and trans-4-propenylsyringol compounds as markers. The second group included guaiacol, 4-methylguaiacol, 4-vinylguaiacol, vanillin, 4-ethylsyringol, 4-vinylsyringol, syringaldehyde, syringylacetone and trans-4-propenylsyringol. It was observed from the statistical analysis that the values of S/G obtained by Py–GC–MS using the two groups of markers did not differ significantly from those obtained by nitrobenzene oxidation method.