Table 1 PLSR quality parameters for cross- and test set-validation for the proposed three cases

Spectral region (cm⁻¹)

3700–2800/1770–1580/1180–1140

3700–2800/2800–2700/1770–1580/1180–1140

3700–3000/1770–1580/1180–1140

Cross-validation

 RMSECV (%)

50.5

73.6

54.3

 Number of PLS components

6

6

6

 R²

0.9945

0.9898

0.9937

External validation

 RMSEP (%)

19.3

28.9

25.2

 Number of PLS components

6

6

6

 R²

0.9988

0.9982

0.9976