[Development of FTIR fingerprint for identification of armand clematis stem (Chuanmutong) and related herbs]

Armand clematis stem (Clematidis Armandii Caulis, Chuanmutong) is a widely used Chinese herb to disinhibit urine and relieve stranguria. It is difficult to be identified owing to its various macroscopic feature and unknown characteristic compounds. Thus, total of 24 Chuanmutong samples and 7 related herbs including four manshurian aristolochia stem (Aristolochiae Manshuriensis Caulis, Guanmutong) and three akebia stem (Akebiae Caulis, Mutong) samples were collected and analyzed in the range of 4 000 - 400 cm⁻¹ by Fourier Transform Infrared (FTIR) and two-dimensional infrared correlation spectroscopy (2D-FTIR) techniques. The FTIR spectra of 24 Chuanmutong samples are consistent in the spectrum profiles, position and intensity of characteristic peaks. 20 of the 24 Chuanmutong samples were randomly selected as calibration samples to calculate and simulate mean spectrum. This mean spectrum is named as FTIR fingerprint of Chuanmutong with characteristic peaks at 3 412, 2 932, 1 739, 1 639, 1 509, 1 456, 1 426, 1 376, 1 332, 1 261, 1 159, 1 035, 897 ,609 cm⁻¹. Meanwhile, the limited level (Mean-3σ=0.992 6) to identify true or false Chuanmutong by correlation coefficient of FTIR spectra was calculated based on the 20 Chuanmutong calibration samples. Then, the rest 4 Chuanmutong, 4 Guanmutong and 3 Mutong samples were used as validation samples to evaluate the identification efficacy. The result shows that the FTIR spectra of 4 Chuanmutong validation samples were similar to the fingerprint. Their correlation coefficients of FTIR spectra were over the limited level and accepted as Chuanmutong. However, the spectra of Guanmutong and Mutong were significantly different from Chuanmutong fingerprint. The correlation coefficients of Guanmutong (0.902 1-0.940 4, n=4) and Mutong (0.954 9-0.978 9, n=3) FTIR spectra were less than the limited level and rejected from Chuanmutong. Furthermore, the number, position and intensity of auto-peaks on the 2D-FTIR were drastically different among the three herbs. It is concluded that the developed FTIR fingerprinting can be rapidly and accurately identify Chuanmutong and differentiate from related herbs.