Mass spectral profiling: an effective tool for quality control of herbal medicines

Abstract

Quality control of herbal medicines (HMs) is a big big headache because of the high complexity and unknown mechanism on disease treatment. In this work, mass spectral profiling, a new tool for data processing is proposed to help a lot in solving this problem as gas chromatography-mass spectroscopy (GC-MS) is used to detect both the active and non-active ingredients buried in HMs. The main idea of mass spectral profiling is employment of target m/z points of GC-MS data on the extraction of chromatographic profiles of pure and/or mixed compositions concerned. Further, the absolute or relative abundance at these m/z points can be utilized for results interpretation. With the help of this tool, the qualitative and quantitative information of chemical components within complicated HMs will be mined out effectively. It can then be recommended as reference indices to assess the importance of target compositions in HMs, such as efficacy evaluation on disease treatment of the active constituents. Mass spectral profiling with less data points significantly improves the possibility to get the rich information with no strong requirements of data preprocessing procedures, like alignment of shift of retention times among different chromatographic profiles. It is powerful for quality control of HMs coupled with pattern recognition techniques on high-throughput data sets. In this study, a commonly used herbal medicine, Houttuynia cordata Thunb and its finished injection products, were used to deliver the strategies. Absolutely, the working principles can be extended to the investigation of metabonomics with gas chromatography-time-of-flight-mass spectrometry (GC-MS-TOF). The good performance of mass spectral profiling shows that it can be a promising tool in the future studies of complex mixture systems.

Fig. 1

Schematic illustration of mass spectral profiling in two-dimensional GC–MS data set X. The mass chromatograms (MC) at certain m/z points and mass spectral profiling at certain retention time (s) are clearly shown in the figure. Also, the chromatographic profiles with pure and mixed chemical components, and selective m/z points at mass spectral profiling are presented for easy understanding purpose.

Fig. 2

The total ion current (TIC) chromatograms of 34 GC–MS data of fresh medicinal materials of Houttuynia cordata Thunb collected from four representative planting areas in China.

Fig. 3

The mean mass spectral profiling of the same GC–MS data shown in Fig. 2 of fresh medicinal materials after sum and normalization operations.

Fig. 4

The four average TIC chromatograms of the samples of final injection products collected from four different manufacturers after alignment of the shift of retention times.

Fig. 5

The clustering results of the samples in Fig. 4 with principal components analysis (PCA) method. Only the first two principal components (PC1 and PC2) are used in the figure. The sub-plot (A) shown in the left above corner is an enlarged figure corresponding to the circled region (a).

Fig. 6

The mean mass spectral profiling of the same GC–MS data in Fig. 4 of final injection products of Houttuynia cordata Thunb after the sum and normalization operations.

Fig. 7

The discrimination results of the mass spectral profiling after deduction of mean of all the 82 samples in Fig. 6 with first 2 principal components PC1 and PC2 by PCA analysis. The two sub-plots (E1 and E2) shown in the left are enlarged figures corresponding to the circled parts of regions A2 and B1, respectively.

Fig. 8

Nine chromatographic profiles with different complexity at the interested m/z points of mass spectral profiling. The three approximately pure profiles with only one chemical component are shown in the first three profiles (1–3). The molecular structures and pure spectra in the figure are information of the three components a–c. Other five mixed chromatographic profiles with two, three, four and more components are extracted from m/z points of the mass spectral profiling.

Fig. 9

Eight chromatographic profiles in two groups (one from 1 to 4, and another from 5 to 8) were acquired at m/z points 58 and 71 of the GC–MS data collected from four different manufacturers, respectively. The quantitative variation information of the target components (such as components a1, a2, a3 and a4; and b1, b2, b3 and b4) of the injection products at the two m/z points can be obtained from the figure.