Application of mid-infrared spectroscopy in analyzing different segmented production of Angelica by AB-8 macroporous resin

Highlights

• Multi-level IR macro-fingerprint method can be applied to study and identify TCM.

• Active components of Angelica can be separated by AB-8 macroporous resin.

• Angelica raw material is rich in sucrose.

• The decoction of Angelica contains polysaccharides, ferulic acid and ligustilide.

• The correlation coefficient with protein of 50% ethanol eluate is highest.

Abstract

As complicated mixture systems, chemical components of Angelica are very difficult to identify and discriminate, so as not to control its quality effectively. In recent years, Mid-infrared spectroscopy has been innovatively employed to identify and assess the quality of Traditional Chinese medicine (TCM) products. In this paper, the macroscopic IR fingerprint method including Fourier transform infrared spectroscopy (FT-IR), the second derivative infrared spectroscopy (SD-IR) and two-dimensional correlation infrared spectroscopy (2D-IR), are applied to study and identify Angelica raw material, the decoction and different segmented production of AB-8 macroporous resin. FT-IR spectrum indicates that Angelica raw material is rich in sucrose and the correlation coefficient is 0.8465. The decoction of Angelica contains varieties of polysaccharides components and the content is gradually decreased with increasing concentration of ethanol. In addition, the decoction of Angelica contains a certain amount of protein components and 50% ethanol eluate has more protein than other eluates. Their second derivative spectra amplify the differences and reveal the potentially characteristic IR absorption bands, then we conclude that the decoction of Angelica contains a certain amount of ferulic acid and ligustilide. And 30% ethanol eluate, 50% ethanol eluate and 70% ethanol eluate are similar to ligustilide. Further, 2D-IR spectra enhance the spectral resolution and obtain much new information for discriminating the similar complicated samples. It is demonstrated that the above three-step infrared spectroscopy could be applicable for effective, visual and accurate analysis and identification of very complicated and similar mixture systems of traditional Chinese medicines.

Introduction

Traditional Chinese medicine (TCM) is one of the oldest and most frequently used medicines worldwide and has influenced various other Asian medical systems [1], [2]. Comprehensive quality control is critical to ensure the efficacy and safety in clinical use. Currently, many methods [3], [4], [5] have been applied to control the quality of medicine, which only involve the qualitative and quantitative assay of one or several chemical markers, such as HPTLC, HPLC, LC–MS, GC–MS, etc. Since the medicinal effects of TCM are determined by the holistic function of various components, the contents of several so-called index components cannot accurately represent the quality of each TCM sample. Besides, as mentioned before, because of quality control methods depending only on a few index components leave the other components uncontrolled, natural medicines could be adulterated by chemical industrial products. Furthermore, these techniques are time-intensive, labour-intensive and expensive [6] and most regulatory bodies concerned with the quality of medicine do not routinely test products [7]. Therefore, it is highly desirable to find a quick and effective identification and discrimination method to entirely monitor and capture the whole constituents of TCM and extract products.

Compared to other analytical techniques, infrared spectroscopic techniques are rapid, nondestructive, effective and low-cost. The IR instruments are commonly configured for mid-infrared (MIR; 4000–400 cm⁻¹) or near-infrared (NIR; 12500–4000 cm⁻¹) analysis. In recent years, both NIR and MIR have been successfully employed to identify TCM. For example, using NIR method to determinate main components in Rhizoma Atractylodis Macrocephalae [8], analysis Honeysuckle extracts [9], discriminate Rhizoma Corydalis from different sources [10]. Applying MIR method to discriminate genuine Glycyrrhizae Radix et Rhizoma and counterfeit Glycyrrhiza pallidiflora Maxim [11], identify wild and cultivated Ginseng [12], [13], differentiate Paeonia lactiflora Pall from different areas [14].

The root of Angelica sinensis (Oliv.) Diels (Umbellifeae), known as Danggui in China, is a famous traditional Chinese medicine in common use [15]. It was first cited in the Shennong Bencao Jing (200–300 A.D., Han Dynasty) [16]. The described functions of Angelica in the Shennong Bencao Jing were to replenish blood, invigorate blood, stop pain, and moisten the intestines. It was reported that the active constituents in Angelica included essential oil and water-soluble substances [17]. In this article, tri-level infrared macro-fingerprint method, Fourier transform infrared spectroscopy (FT-IR) associated with second derivative infrared spectroscopy and two-dimensional correlation infrared spectroscopy (2D-IR) were applied to study the holistic variation rules of chemical constituents in Angelica and its different segmented production of HPD-100 macroporous resin. The aim of this study is to develop an effective analysis method for studying integrally the main constituents in the medicinal materials and their corresponding extracts, comparing the categories of chemical constituents in the different extracts and monitoring the qualities of medicinal materials.