Differentiation of Rhizoma Curcumas Longae and Radix Curcumae by a Multistep Infrared Macro-Fingerprint Method

Abstract

A multistep infrared macro-fingerprint method was applied to identify two Chinese herbal drugs, Rhizoma Curcumas Longae (RCL) and Radix Curcumae (RC). Fourier transform infrared (FT-IR) spectra of the two were similar to each other and consistent with the 11 peaks of the spectrum of starch. RCL had a characteristic absorption peak at approximately 1514 cm⁻¹ that correlated to the strong peak near 1509 cm⁻¹ of curcumin. Between 900 cm⁻¹–1700 cm⁻¹ of the second derivative infrared (SD-IR) spectra, with higher resolution, RCL, and curcumin had 10 common peaks. In the FT-IR and SD-IR spectra of the ethanol extract, the spectra of the RCL extract and curcumin were similar, but RC was different. According to the fingerprint characteristics of the infrared spectra for RC and its extracts, the strongest peak at 1055 cm⁻¹; the C-O absorption peaks at 1124 cm⁻¹, 1106 cm⁻¹, and 996 cm⁻¹; and the strong methylene peaks at 2925 cm⁻¹ and 2853 cm⁻¹ suggest that RC contains more saccharides. In the range of 1350 cm⁻¹–1700 cm⁻¹, RCL and RC had similar two-dimensional infrared (2D-IR) correlation spectra. Both of them had three autopeaks, but the autopeaks were located at 1458 cm⁻¹, 1560 cm⁻¹, and 1641 cm⁻¹ for RCL and 1458 cm⁻¹, 1560 cm⁻¹, and 1669 cm⁻¹ for RC, suggested that the aromatic components of the two were not identical. The average correlation for the 18 RCL and 18 RC samples were 0.9906 and 0.9878, respectively, and this method achieves a good classification of the sample type.

Keywords:

• 2D-IR correlation spectroscopy
• FT-IR
• Multistep infrared spectroscopy
• Radix curcumae
• Rhizoma curcumas longae

Acknowledgments

This work is sponsored by the State Administration of Traditional Chinese Medicines of the People's Republic of China (2001ZDZX01), received grant support from the National Basic Research Program of China (2006CB504700) and is supported by the China Academy of Chinese Medical Sciences (Z02078).

Notes

Z.-J. Zhang and H.-M. Li contributed equally to this work.