Rapid discrimination of three kinds of Radix Puerariae and their extracts by Fourier transform infrared spectroscopy and two-dimensional correlation infrared spectroscopy

In this study, a macroscopic IR fingerprint method, conventional Fourier transform infrared spectroscopy (FT-IR) combined with second derivative infrared spectroscopy and two-dimensional correlation infrared spectroscopy (2D-IR), was applied to quickly identify three kinds of Radix Puerariae and their ethanol extracts (AL extracts). They are authenticated as Pueraria thomsonii Benth (PTB), Pueraria lobata (Willd.) Ohwi (PLW) and simmered P. lobata (Willd.) Ohwi (PLS). By comparing the IR spectra and correlation coefficients, PTB, PLW and PLS all have comparable profiles to starch, however, PTB has relatively higher content starch comparing to PTB and PLW, and on the other hand PLW and PLS have relatively more puerarin than PTB. Though the IR spectra of PLW and PLS were almost the same, significant differences were found in 2D-IR spectra with much higher resolution. The strongest auto-peaks are at 1636 cm−1 and 1654 cm−1 in PLW and PLS, while the relative intensities are different. Moreover, the AL extracts of the three medicines were also perceivably distinguished step by step with FT-IR and 2D-IR. For example, cross-peaks at (1518, 1561) and (1518, 1568) with PLW are superior to PLS. The AL extracts had much higher correlation coefficients with puerarin than their corresponding raw materials. The contents of puerarin in the AL extracts followed the order: PLW > PLS > PTB. Therefore, it was demonstrated that the macroscopic fingerprint method of FT-IR and 2D-IR spectroscopy could be used to discriminate the three types of Radix Puerariae and their ethanol extracts rapidly and effectively.