Identification of Dalbergia cochinchinensis (CITES Appendix II) from other three Dalbergia species using FT-IR and 2D correlation IR spectroscopy

In order to develop a fast and effective method to distinguish D. cochinchinensis from some easily confused species, FT-IR and 2DCOS-IR spectroscopy were used to study D. cochinchinensis, D. retusa, D. bariensis, and D. oliveri. Specific stable differences were found in the IR spectra helpful to distinguish D. cochinchinensis from the other three similar species. It was revealed that there was a peak at 738 cm−1 present in all 17 available heartwood specimens of D. retusa, but it was not detected in the 19 samples of D. cochinchinensis. All 19 samples of D. cochinchinensis had two peaks at 755 and 701 cm−1 which did not occur in all 10 specimens of D. bariensis and D. oliveri. Further study revealed that these peaks were attributed to their extractives, indicating that the chemical composition of their extractives had some differences. Calcium oxalate crystals with characteristic absorption peaks at 1618, 1318, and 782 cm−1 only occurred in D. bariensis and D. oliveri, but were not found in D. cochinchinensis. In addition, as suggested by the 2DCOS-IR spectra of the benzene–alcohol extractives of these four Dalbergia species, the benzene–alcohol extractives of D. cochinchinensis were more stable to thermal perturbation than the others. In conclusion, IR technique can provide persuasive evidence to distinguish the heartwood of D. cochinchinensis from D. retusa, D. bariensis, and D. oliveri.