Table 1.
Approximate positions of NIR bands that are meaningful for samples of biological origin (excluding water). In brackets provided are the exemplary chemical compounds for which the transitions are specific. The assignments adopted from literature [9,11].
| Wavenumber in cm−1 | Wavelength in nm |
Vibrational Mode Assignment and the Associated Most Characteristic Compounds a) |
|---|---|---|
| 8250 | 1210 | 3 C–H str. (C-H rich compounds, e.g., carbohydrates, lipids) |
| 7375–7150 | 1355–1400 | 2 C–H str. + C–H def. (carbohydrates, lipids) |
| 6980 | 1435 | 2 N–H str. (proteins) |
| 6750 | 1480 | 2 O–H str. (carbohydrates, alcohols, polyphenols) |
| 6660 | 1500 | 2 N–H str. (proteins) |
| 6500 | 1540 | 2 O–H str. (carbohydrates, alcohols, polyphenols upon matrix effects, e.g., hydrogen bonded OH groups) |
| 6400 | 1565 | 2 N–H str. (proteins) |
| 6200–5800 | 1610–1725 | 2 C–H str. (carbohydrates, lipids) |
| 5625 | 1780 | 2 C–H str. (C-H rich compounds, e.g., carbohydrates, lipids) |
| 5500 | 1820 | O–H str. + 2 C–O str. (carbohydrates) |
| 5120 | 1955 | 3 C–O str. (carbohydrates) |
| 4880 | 2050 | N–H sym. str. + amide II (proteins) |
| 4825 | 2075 | O–H str. + O–H def. (alcohols, polyphenols) |
| 4645 | 2155 | Amide I + amide III (proteins) |
| 4440 | 2255 | O–H str. + O–H def. (carbohydrates, alcohols, polyphenols) |
| 4360 | 2295 | N–H str. + CO str. (proteins) |
a) Numbers two and three denote the first and second overtones, respectively; plus sign (+) denotes combination bands.