. 2014 Sep 15;9(9):e107285. doi: 10.1371/journal.pone.0107285

Table 3. Frequencies and assignments of the main peaks identified in the analysis of FTIR spectra.

Wave number, cm⁻¹	Assignment	Characterisation
3522,3400	O-H stretching	Gypsum¹ ^{, 2}
3340	O-H stretching	Cellulose, in samples with defined 3340 peak³
2920	antisymmetric CH₂ stretching	Fats, wax, lipids³
2850	symmetric CH₂ stretching	Fats, wax, lipids³
1740-1720	C = O stretch of COOR	Esters^{3, 4}
1707-1710	C = O stretch of COOH	Carboxylic acids^{3, 4}
1653	C = O of amide I	Proteinaceous origin³
1615	C-O stretching	Calcium oxalate⁵
1600-1650 (1610)	Aromatic C = C stretching and/or asymmetric C-O stretch in COO-	Lignin and other aromatics, or aromatic or aliphatic carboxylates³
1550	N-H in plane (amide-II)	Proteinaceous origin³
1505-1515	Aromatic C = C stretching	Lignin/Phenolic backbone^{3, 4}
1450-1410	C-O stretching	Calcium carbonate^{4, 6}
1426	Symmetric C-O stretch from COO- or stretch and OH deformation (COOH)	Carboxylate/Carboxylic structures (humic acids)³
1371, 1450	C-H deformations	Phenolic (lignin) and aliphatic structures³
1312	C-O stretching	Calcium oxalate⁵
1265 (approx.)	C-O stretching of phenolic OH and/or arylmethylethers	Indicative of lignin backbone³
1265 -1240	C-O-C stretching	Esters
	C-N stretching	Amide III⁴
1140-1080	S-O stretching	Sulphates⁴
1100-1000	P-O stretching	Phosphates⁶
1100-950	Si-O stretching	Silicates^{4, 6}
1050 (1030-1080)	Combination of C-O stretching and O-H deformation	Polysaccharides³
874	C-O in plane bending	Calcium carbonate^{4, 6}
835	Aromatic CH out of plane	Lignin³
780	COO bending	Calcium oxalate⁵
720	CH₂ wag	Long chain (> C4) alkanes³
715	C-O in plane bending	Calcium carbonate^{4, 6}
680-610	S-O bending	Sulphates⁴
669,597	S-O bending	Gypsum¹ ^{, 2}

[39]; ² [56]; ³ [38]; ⁴ [21]; ⁵ [57]; ⁶ [58].