•Principal components of Aquilariae Lignum Resinatum (ALR) are profiled by FT-IR.•Thermal stability of the principal components of ALR is studied by 2D-IR.•An identification method for ALR is established based on the spectral correlations.•Commercial adulteration methods for ALR are revealed by IR spectral features.As a kind of expensive perfume and valuable herb, Aquilariae Lignum Resinatum (ALR) is often adulterated for economic motivations. In this research, Fourier transform infrared (FT-IR) spectroscopy is employed to establish a simple and quick method for the adulteration screening of ALR. First, the principal chemical constituents of ALR are characterized by FT-IR spectroscopy at room temperature and two-dimensional correlation infrared (2D-IR) spectroscopy with thermal perturbation. Besides the common cellulose and lignin compounds, a certain amount of resin is the characteristic constituent of ALR. Synchronous and asynchronous 2D-IR spectra indicate that the resin (an unstable secondary metabolite) is more sensitive than cellulose and lignin (stable structural constituents) to the thermal perturbation. Using a certified ALR sample as the reference, the infrared spectral correlation threshold is determined by 30 authentic samples and 6 adulterated samples. The spectral correlation coefficient of an authentic ALR sample to the standard reference should be not less than 0.9886 (p = 0.01). Three commercial adulterated ALR samples are identified by the correlation threshold. Further interpretation of the infrared spectra of the adulterated samples indicates the common adulterating methods - counterfeiting with other kind of wood, adding ingredient such as sand to increase the weight, and adding the cheap resin such as rosin to increase the content of resin compounds. Results of this research prove that FT-IR spectroscopy can be used as a simple and accurate quality control method of ALR.

•Multiple FT-IR methods are proposed for the direct characterization of wood resins.•Temperature-resolved FT-IR can interpret the compounds of wood resin exudates.•FT-IR spectroscopic imaging can resolve the compounds of resin-containing woods.•FT-IR can be a useful tool for the research and quality control of wood resins.Wood resins are valuable natural products with wide utilizations. Either in the form of resin exudates or in the form of resin-containing woods, natural wood resins are usually complex mixtures consisting of various compounds. Therefore, effective chemical characterization methods are necessary for the research and quality control of natural wood resins. No need for separation or labeling, wood resin samples can be measured directly by Fourier transform infrared (FT-IR) spectroscopy, which reduces the testing costs and avoids the possible distortions caused by the pretreatments. However, the absorption bands of various compositions in the resin sample are assembled in a single spectrum by the separation-free measurement, which makes it difficult to identify the compounds of interest and decreases the limits of detection. In this research, the temperature-resolved and space-resolved FT-IR techniques are proposed to resolve the overlapped signals for the direct, selective, and sensitive characterization of natural wood resins. For resin exudates, the temperature-resolved FT-IR spectroscopy and two-dimensional correlation analysis can resolve the absorption bands of different compounds according to their responses to the thermal perturbations. For resin-containing woods, the FT-IR microspectroscopic imaging and principal component analysis can resolve the absorption bands of different compounds according to their positions. The study of six kinds of wood resins proves the feasibility of temperature-resolved and space-resolved FT-IR techniques for the direct, selective, and sensitive chemical characterization of natural wood resins.

•FT-IR spectroscopy is used to identify Lonicerae japonicae Flos and Lonicerae Flos.•These herbs show discriminating peaks near 1534, 1404 and 781 cm−1 in FT-IR spectra.•Derivative spectra show differences near 1078, 1050, 988, 923, 855, 815 and 781 cm−1.•Differences between these herbs in 2D-IR spectra are intuitive and remarkable.Lonicerae japonicae Flos (LJF) and Lonicerae Flos (LF) are widely-used herbs derived from several plants of the genus Lonicera with similar appearances. LF are usually misused or counterfeited as LJF for economically motivated adulteration. However, the saponins in LF may cause serious side-effects. In this research, the infrared spectroscopic tri-step identification approach is used to develop a simple and rapid method to discriminate LJF and LF to ensure the safety and efficacy of these herbal drugs. In the primary identification by Fourier transform infrared spectra, LJF and LF show different peaks near 1534, 1404, and 781 cm−1. In the secondary identification by the second derivative infrared spectra, LJF and LF show more different peaks near 1078, 1050, 988, 923, 855, 815, and 781 cm−1. In the tertiary identification by the two-dimensional correlation infrared spectra, the differences between LJF and LF are shown more remarkably and convincingly. The results show the potential of the infrared spectroscopic tri-step identification approach in the rapid identification of LJF and LF when the samples are too few to build a statistical recognition rule. This should be very helpful to ensure the quality, safety, and efficacy of LJF and LF for clinical applications.

•Standard and adulterated Aquilariae Lignum Resinatum are studied by FT-IR and 2D-IR.•FT-IR shows that the adulterated samples contain little or different resin compounds.•Differences between standard and adulterated samples are remarkable in 2D-IR spectra.•FT-IR and 2D-IR can identify Aquilariae Lignum Resinatum simply and quickly.As a kind of expensive perfume and valuable herb, the commercial Aquilariae Lignum Resinatum (ALR) is often adulterated for economic motivations. In this research, Fourier transform infrared (FT-IR) spectroscopy and two-dimensional (2D) correlation analysis are employed to establish a simple and quick identification method for the authentic and adulterated ALR. In the conventional infrared spectra, the standard ALR has a strong peak at 1658 cm−1 referring to the conjugated carbonyl of resin, while this peak is absent in the adulterated samples. The position, intensity, and shape of the auto-peaks and cross-peaks of the authentic and adulterated ALR are much different in the synchronous 2D correlation spectra with thermal perturbation. In the range of 1700–1500 cm−1, the standard ALR has four obvious auto-peaks, while the strongest one is at 1659 cm−1. The adulterated sample w-1 has three obvious auto-peaks and the strongest one is at 1647 cm−1. The adulterated sample w-2 has three obvious auto-peaks and the strongest one is at 1519 cm−1. The adulterated sample w-3 has four obvious auto-peaks and the strongest one is at 1690 cm−1. The above auto-peaks confirm that the standard ALR contains a certain content of resin compounds, while the three counterfeits contain little or different resins. The results show the potential of FT-IR spectroscopy and 2D correlation analysis in the simple and quick identification of authentic and adulterated ALR.Figure: Synchronous 2D-IR spectra of authentic ALR (a) and adulterated samples (b-d)

•A simple and sensitive screening approach for adulterated plant samples is proposed.•IR spectroscopic imaging is used to cluster the entities in a plant sample.•2DCOS can indicate the clustering is caused whether by adulteration or not.•The feasibility of this approach is proved by a model sample of adulterated saffron.Infrared (IR) spectroscopy is often used as a simple, fast, and green method for the adulteration screening of botanical materials for foods and herbs. However, the overlapping of absorption signals of various substances significantly decrease the sensitivity and specificity of IR spectroscopy in the detection of adulterated samples. In this research, a model-free approach is proposed for the sensitive and non-targeted screening of botanical materials adulterated by adding other plant materials. First, the spectra of the entities in the test sample are collected by near-infrared spectroscopic imaging and clustered by unsupervised pattern recognition methods. The sample may be adulterated if there are two or more clusters of the entities. Next, the entities of different clusters are characterized by mid-infrared spectroscopy to interpret the chemical compositions to determine the clustering is caused whether by adulteration or other reasons. Second derivative spectroscopy and two-dimensional correlation spectroscopy are often needed to resolve the overlapped bands mathematically or experimentally to find the characteristic signals to identify the authentic and adulterant entities. The feasibility of this approach was proved by the simulated adulterated sample of saffron. In conclusion, botanical materials adulterated by adding other plant materials can be detected by a simple, fast, sensitive, and green screening approach using IR spectroscopic imaging, two-dimensional correlation spectroscopy, and necessary chemometrics techniques.

Before their medical use, thermal processing methods are frequently utilized to treat the traditional Chinese herbal materials to improve their efficacy or reduce their side effects. Understanding the temperature-dependent chemical reactions of herbal materials is necessary to explore the mechanisms and optimize the procedures of thermal processing. Being a quick, label-free, and nondestructive analytical technique, infrared (IR) spectroscopy can be used to in situ monitor the changes of herbal materials as the temperature increases continually. In this research, the thermal processing of Gardeniae fructus (the ripe fruit of Gardenia jasminoides Ellis) was studied by thermogravimetry-infrared spectroscopy (TG-IR) and heated transmission IR spectroscopy. In summary, the decrease in organic acids (chlorogenic acid, quinic acid, ursolic acid, etc.) is the main reason why thermal processing can reduce the side effects of Gardeniae fructus on intestines and stomach. Stir-baking to yellow at 125–145 °C can reduce the amount of the organic acids remarkably, while most iridoids such as geniposide remain to retain the medical functions of Gardeniae fructus in clearing pathogenic heat, lessening the virulence of pathogens, reducing blood pressure, etc. Stir-baking to brown at 145–165 °C can further reduce the organic acids, but the iridoids also decompose significantly. Stir-baking to scorch at 165–190 °C will destroy most iridoids, but the tannins change the function of Gardeniae fructus into hemostasis.

In this study, a convenient method using multi-step infrared spectroscopy, including Fourier transform infrared spectroscopy (FT-IR), second derivative infrared spectroscopy (SD-IR) and two-dimensional correlation infrared spectroscopy (2DCOS-IR), was employed to analyze and discriminate ten marine sponges from two classes collected from the Xisha Islands in the South China Sea. Each sponge had an exclusive macroscopic fingerprint. From the IR spectra, it was noted that the main ingredient of calcareous sponges was calcium carbonate, but that of demosponges was proteins. For sponges from the same genus or having highly similar chemical profile (IR spectral profile), SD-IR and 2DCOS-IR were applied to successfully reveal the tiny differences. It was demonstrated that the multi-step infrared spectroscopy was a feasible and objective approach for marine sponge identification.Ten sponges from two classes and six orders were discriminated by multi-step IR. Sponges of the same genus were definitely discriminated by 2DCOS-IR.

•Four Deodeoks of different growth years were analyzed thoroughly by a three-level IR spectroscopy method.•Ethanol and aqueous extracts of Deodeoks of different growth years were also distinguished effectively.•2D-IR spectra indicated different Deodeok samples varied with response to temperature.Deodeok (Codonopsis lanceolata) root, a traditional Chinese herbal medicine, has been used to treat lung ailments, rheumatism, menstrual disturbance and bruises with a long history in China and some other Asian countries. In this study, four types of Deodeok with different growth years were discriminated and identified by a Tri-step infrared spectroscopy method (Fourier transform-infrared spectroscopy (conventional FT-IR) coupled with second derivative infrared spectroscopy (SD-IR) and two dimensional correlation infrared spectroscopy(2DCOS-IR) under thermal perturbation. Although only small differences were found in the FT-IR spectra of the samples, the positions and intensities of peaks around 1736, 1634, 1246, 1055, 1033, 818, 779 cm−1 could be considered as the key factors for discriminating them. The differences among them were amplified by their SD-IR spectra. The 2DCOS-IR spectra provided obvious dynamic chemical structure information of Deodeok samples, which present different particular auto peak clusters in the range of 875–1130 cm−1 and 1170–1630 cm−1, respectively. It was demonstrated that the content of triterpene were decreasing when C. lanceolata were growing older, but the relative content of saccharides initially increased and decreased significantly afterwards. It indicated a general trend that the content of polysaccharides accumulated with increasing years. Specifically, the content of polysaccharides accumulated in the root of 2-year-old plant was the lowest, 4-years-old was the highest, and then the content decreased gradually. Furthermore, according to the differences of locations and intensities of auto-peaks in 2D-IR spectra, the integral changes of components were revealed. This study offers a promising method inherent with cost-effective and time-saving to characterize and discriminate the complicated system like Deodeok.

•A stepwise analysis-through-separation approach based on multi-stage IR spectra (FT-IR, the second derivative IR and 2DCOS-IR) method was developed for analysis of the separation process of licorice.•Group-peak matching technique and spectral correlation coefficients were employed for the analysis.•The chemical compositions of licorice were comprehensively displayed from entirety to single active components.•The findings were supported by UPLC and a verification experiment of aqueous separation process.In this paper, a step-by-step analysis-through-separation method under the navigation of multi-step IR macro-fingerprint (FT-IR integrated with second derivative IR (SD-IR) and 2DCOS-IR) was developed for comprehensively characterizing the hierarchical chemical fingerprints of licorice from entirety to single active components. Subsequently, the chemical profile variation rules of three parts (flavonoids, saponins and saccharides) in the separation process were holistically revealed and the number of matching peaks and correlation coefficients with standards of pure compounds was increasing along the extracting directions. The findings were supported by UPLC results and a verification experiment of aqueous separation process. It has been demonstrated that the developed multi-step IR macro-fingerprint analysis-through-separation approach could be a rapid, effective and integrated method not only for objectively providing comprehensive chemical characterization of licorice and all its separated parts, but also for rapidly revealing the global enrichment trend of the active components in licorice separation process.

Although herbal medicine (HM) behaves as a complex system having high-potential for treating chronic/life-threatening diseases, compatible characterization metrics with hierarchical approaches to integrate molecular-level information into the whole system are lacking. Herein, we report a high-throughput methodology (holographic infrared (IR) spectroscopy) harmonizing with the character of HM, providing hierarchical infrared fingerprints (entirety, parts and single ingredients), and working as a “GPS” to navigate a comprehensive chemical characterization of HM circularly from system to molecular level by step-by-step HM analysis-through-separation of IR spectra indicative and vice versa by reconstitution-through-combination of adducting spectrum without a complete understanding of the chemical constituents, and demonstrate holographic chemical charaterization of a Chinese herb Danshen. Global chemical fingerprints of species at each hierarchical level and ingredient profile variations among multilevel species of Danshen are integratively interpreted with fast estimation of their relative contents of active compounds. Finally, integral dynamic information of Danshen separation process is disclosed straightforward by spectral retrieving technique.

It has been proved to be a very useful method to distinguish similar samples by two-dimensional correlation spectroscopy when they are hardly distinguished by the conventional one-dimensional spectroscopy. To acquire the quantitative description of the differences between samples, the similarity of the series dynamic spectra, which reflects the similarity of the samples themselves if obtained under the same perturbation condition, is evaluated by the symmetry of hetero 2DCOS map. Two parameters, the Euclidian distance and correlation coefficient between the upper left and lower right triangular parts of a hetero 2DCOS map, are introduced for the quantitative measure of the symmetry, which in turn characterizes the similarity of the responses of samples to a given perturbation. The above method is used to discriminate one genus of Astragalus from the others to ensure the medicinal efficacy and safety of the herb. Hypothesis tests show that the inter-distances between samples from different genera are significantly larger than the intra-ones within the same genera, while the inter-correlation coefficients are smaller than the intra-ones. The excellent result of the identification for all samples carried out by a t-test based on the distances indicates that this method provides an efficient technique for the quantitative evaluation of similarity between samples.