Table 2.
Results of PLS regression between molecular weight and inter‐unit abundances determined by GPC and 2D HSQC NMR spectroscopy for the 28 kraft lignin samples and their ATR‐FTIR spectra using 1st derivative pre‐processing.[a]
| Entry | Unit | Range | Num. LVs | Calibration (28 samples) | Validation (2×7 samples) | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| RMSEC | RMSECV | RE [%] | R 2 Cal. | R 2 CV | RMSEP | R 2 Pred. | ||||
| 1 | M n | 4570 | 6 | 210 | 410 | 9.0 | 0.97 | 0.89 | 810 (510)[c] | 0.87 (0.98)[c] |
| 2 | log(M n) | 0.91 | 5 | 0.025 | 0.046 | 5.0 | 0.99 | 0.97 | 0.087 (0.050)[c] | 0.96 (0.99)[c] |
| 3 | M w | 29 984 | 6 | 1430 | 3100 | 10 | 0.96 | 0.81 | 3400 | 0.89 |
| 4 | log(M w) | 1.7 | 6 | 0.039 | 0.097 | 5.8 | 0.99 | 0.95 | 0.094 | 0.98 |
| 5 | D | 4.9 | 6 | 0.22 | 0.51 | 10 | 0.97 | 0.84 | 0.72 | 0.98 |
| 6 | β‐O‐4 | 12 | 6 | 0.25 | 0.46 | 3.8 | 1.00 | 0.99 | 0.56 | 0.98 |
| 7 | β‐5 | 3.8 | 6 | 0.095 | 0.18 | 4.7 | 0.99 | 0.98 | 0.27 | 0.97 |
| 8 | β‐β | 1.8 | 3 | 0.13 | 0.19 | 10 | 0.94 | 0.87 | 0.15 | 0.94 |
| 9 | SB5 | 8.0 | 3 | 0.79 | 1.0 | 13 | 0.87 | 0.79 | 1.2 | 0.90 |
| 10 | SB1 | 7.9 | 5 | 0.26 | 0.48 | 6.1 | 0.98 | 0.94 | 0.39 | 0.94 |
[a] Values reported to 2 significant figures; see Figure S3 for the regression vectors associated with these models. [b] Pred.=predicted. [c] The relatively large RMSECV/RMSEP ratio can indicate overfitting. In this case it results from an outlier sample in the M n measurements due to the poor solubility of the acetone/MeOH fraction in the GPC solvent. Exclusion of this data results in a better prediction (shown in brackets).