Table 1. Lignin Interunit Linkage Type Contents from Integration of 2D HSQC NMR Spectra of Lignin Extracted from Norway Spruce Inner Barka.
| OSL | MBL | MRL | |
|---|---|---|---|
| β-O-4′ aryl ethers | 30 ± 2 | 31 | 17 |
| β-5′phenylcoumarans | 12 ± 1 | 12 | 6.2 |
| β–β′resinols | 1.9 ± 0.2 | 2.2 | 1.9 |
| 5-5′ dibenzodioxocins (DBDO) | 0.5 ± 0.2 | 3.8 | 0.1 |
| enolether | 1.3 ± 0.1 | 1.0 | |
| coumaraldehyde | 2.3 ± 0.2 | 0.8 | |
| Hibbert’s ketone | 2.0 ± 0.1 | 1.2 | 2.1 |
| Stilbene-β1 | 3.5 ± 0.5 | 1.4 | 1.1 |
| Stilbene-β5 | 3.0 ± 0.3 | 0.4 | 1.5 |
a
The results of the OSL linkage values are the mean of four measurements and the corresponding standard deviation. The standard deviation also applies for the measurement of MBL and MRL; OSL—lignin extracted by organosolv extraction, MBL—milled raw bark extracted with dioxane, and MRL—milled residue after organosolv treatment extracted with dioxane. The interunit linkages are semiquantified per 100 Ar units using the C2 region in the aromatic region as an internal standard.