Rapid and automatic chemical identification of the medicinal flower buds of Lonicera plants by the benchtop and hand-held Fourier transform infrared spectroscopy

https://doi.org/10.1016/j.saa.2017.03.070Get rights and content

Highlights

  • For the first time the hand-held FT-IR spectrometer is used for herb identification.

  • The medicinal flower buds of five kinds of Lonicera plants are discriminated.

  • Benchtop and hand-held FT-IR recognition models are built for lab and field demands.

  • Hand-held FT-IR shows great potential in the process analysis of herbal materials.

Abstract

With the utilization of the hand-held equipment, Fourier transform infrared (FT-IR) spectroscopy is a promising analytical technique to minimize the time cost for the chemical identification of herbal materials. This research examines the feasibility of the hand-held FT-IR spectrometer for the on-site testing of herbal materials, using Lonicerae Japonicae Flos (LJF) and Lonicerae Flos (LF) as examples. Correlation-based linear discriminant models for LJF and LF are established based on the benchtop and hand-held FT-IR instruments. The benchtop FT-IR models can exactly recognize all articles of LJF and LF. Although a few LF articles are misjudged at the sub-class level, the hand-held FT-IR models are able to exactly discriminate LJF and LF. As a direct and label-free analytical technique, FT-IR spectroscopy has great potential in the rapid and automatic chemical identification of herbal materials either in laboratories or in fields. This is helpful to prevent the spread and use of adulterated herbal materials in time.

Introduction

Identification of botanical origins is the first and foremost step in assuring the quality of herbal materials [1], [2]. Compared with the morphological and histological identification methods depended on personal experience, the chemical identification methods using chromatographic or spectroscopic techniques have the advantages of objectivity and quantification. However, the benchtop instruments and time-consuming procedures are often required for the chemical identification methods. This means that herbal materials have to be transported to laboratories for testing, which may cost several days or more time to get the results. It is necessary to reduce the delay between sampling and identifying to prevent the spread and use of adulterated herbal materials in time.

Fourier transform infrared (FT-IR) spectroscopy has great potential in minimizing the time cost for the chemical identification of herbal materials [3], [4]. Since FT-IR spectroscopy is a direct and label-free analytical technique, herbal samples can be measured without any separation or derivation. A spectrum can be obtained and interpreted in seconds to minutes. Consequently, FT-IR spectroscopy has been more and more popular for the chemical identification of herbal materials [5], [6], [7], [8], [9], [10], [11]. But, as far as the authors know, only the benchtop FT-IR spectrometers are employed in current reports. In order to test herbal materials immediately at anytime and anywhere as needed, it is necessary to develop chemical identification methods using the hand-held FT-IR equipment for on-site applications. Therefore, this research is going to examine the feasibility of the hand-held FT-IR spectrometer for the chemical identification of herbal materials, using Lonicerae Japonicae Flos (LJF) and Lonicerae Flos (LF) as examples.

Both LJF and LF are common traditional Chinese herbs [12], [13]. LJF consists of the flower buds of Lonicera japonica Thunb., while LF consists of the flower buds of other four kinds of plants of the same genus. The appearances of LJF and LF are quite similar (Fig. 1), which makes it difficult to distinguish these materials by morphological features. However, LF provides weaker medical efficacy but more serious side effects than LJF [14], [15]. The accurate identification of LJF and LF is required to assure the safety and efficacy of these materials for pharmaceutical and dietary supplement applications.

Section snippets

Materials

LJF and LF articles used in this research were collected from the main habitats of the original plants in China. 23 LJF articles consist of the dried flower buds of L. japonica Thunb. were from Shandong, Henan, and Hebei. LF articles consists of the dried flower buds of L. confusa DC. (LF-C), L. fulvotomentosa Hsu et S. C. Cheng (LF-F), L. hypoglauca Miq. (LF-H), or L. macranthoides Hand. -Mazz. (LF-M). 12 LF-C articles were from Guangdong, 8 LF-F articles were from Guizhou, 8 LF-H articles

Benchtop FT-IR Spectral Characteristics of LJF and LF

Fig. 2 shows the average spectra of LJF and LF measured by the benchtop FT-IR instrument and the KBr pellet method. Assignments of the main absorption peaks are summarized in Table 1. Complex compositions of herbal samples often lead to overlapped absorption peaks in the infrared spectra. The derivative spectra can resolve envelope bands to reveal the underlying peaks, which is helpful to find the spectral features of compounds of interest [17].

As shown in Fig. 2a, the benchtop spectra of LJF

Conclusion

The benchtop and hand-held FT-IR spectrometers are employed to establish the chemical identification models for LJF and LF. Correlation-based linear discriminant models using the benchtop FT-IR spectra can exactly recognize all articles of LJF and LF. Although the models using the hand-held FT-IR spectra misjudge a few articles of LF in the sub-class level, all articles of LJF and non-LJF can be discriminated, which is acceptable for the adulteration screening. This research proves the

Competing interests

The authors declare that they have no competing interests.

Acknowledgements

We thank National Natural Science Foundation of China (No. 31370556) for the financial support.

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