Suggested peak shifts based on hide and leather FTIR spectra. Peaks associated with amide bonding were the primary shifted structures, and commonly gained peak shoulders after tanning.
| Peaks | Wavenumbers (cm−1) before and after tanning | ||
|---|---|---|---|
| Cowhide | Vegetable tanned leather | Shift | |
| Amide A | 3300 | 3300 | No |
| Lipid I | 2920 | 2920 | No |
| Lipid II | 2850 | 2850 | No |
| Lipid III | 1740 | 1740 | No |
| Amide I | 1630 | 1620, 1650 | Yes |
| Amide II | 1535 | 1535, 1515 | Yes |
| Hydroxyproline residue | 1450 | 1450 | No |
| Amide III | 1400, 1335, 1235 | 1365, 1335, 1315, 1225 | Yes |
| Lipid IV | 1160 | 1160 | No |
| Unassigned II | 1080 | — | No |
| Unassigned III | 1030 | — | No |