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. 2018 Nov 15;23(11):2988. doi: 10.3390/molecules23112988

An Integrated LC-MS-Based Strategy for the Quality Assessment and Discrimination of Three Panax Species

Zhixia Du 1,2,†, Jinhua Li 2,†, Xiang Zhang 2, Jin Pei 1,*, Linfang Huang 2,*
PMCID: PMC6278395  PMID: 30445785

Abstract

The quality assessment and discrimination of Panax herbs are very challenging to perform due to the complexity and variability of their chemical compositions. An integrated strategy was established using UHPLC-Q-Exactive/HRMS and HPLC-ESI-MS/MS to achieve an accurate, rapid, and comprehensive qualitative and quantitative analysis of Panax japonicas (PJ), Panax japonicus var. major (PM), and Panax zingiberensis (PZ). Additionally, discrimination among the three species was explored with partial least squares–discriminant analysis (PLS-DA) and orthogonal partial least squares–discriminant analysis (OPLS-DA) score plots. A total of 101 compounds were plausibly or unambiguously identified, including 82 from PJ, 78 from PM, and 67 from PZ. Among them, 16 representative ginsenosides were further quantified in three herbs. A clear discrimination between the three species was observed through a multivariate statistical analysis on the quantitative data. Nine compounds that allowed for discrimination between PJ, PM, and PZ were discovered. Notably, ginsenoside Rf (G-Rf), ginsenoside F3 (G-F3), and chikusetsu saponin IV (CS-IV) were the three most important differential compounds. The research indicated that the integrated LC-MS-based strategy can be applied for the quality assessment and discrimination of the three Panax herbs.

Keywords: qualitative analysis, quantitative analysis, ginsenosides, panax species, UHPLC-Q-Exactive/HRMS

1. Introduction

Ginseng herbs, the roots and rhizomes of the Panax species (Araliaceae), are valuable traditional herbs that have a thousand years of medical history and are well-known worldwide as herbal medicines and food to enhance body strength, prevent exhaustion, and improve immunity [1]. Panax species are the important medicinal resources in the world because of their significant medicinal value, and are distributed in more than 35 countries, particularly America, South Korea, Japan, and China. With their popularity all over the world, the attention that Panax has received has increased significantly [2,3,4,5]. These herbs contain complex chemical constituents. Ginsenosides are the characteristic and principal components and have been used as an important index in quality assessment and control. The skeleton of aglycones reveals dammarane tetracyclic triterpenoidal saponins and oleanane pentacyclic triterpenoidal saponins (oleanolic acid-type ginsenosides, OAs) in natural ginsensides. Furthermore, dammarane tetracyclic triterpenoidal saponins can be divided into protopanaxatiol-type ginsenosides (PPTs) and protopanaxadiol-type ginsenosides (PPDs) according to the study of dammarane structures [6]. Although numerous analytical approaches have been applied for the qualitative and quantitative analysis of ginsenosides, including UV, IR, TLC, HPLC, and UPLC, the analysis of ginsenosides is still a great challenge because of the diversity, similarity, and complexity of their chemical structures [1].

In recent years, some advanced analytical techniques have been rapidly developed for the quality assessment and control of traditional herbs. Q-Exactive Orbitrap High-Resolution Mass Spectrometry (Q-Exactive/HRMS) is a recently developed technique with extremely high resolution, sensitivity, and mass accuracy. It exhibits a stronger power for the scanning and identification of complex compounds than normal mass spectrometry [7]. LC-HRMS is now a well-established technique for the qualitative analysis of chemical compounds in metabolomic studies, and has seen significant progress in recent years [1]. Combining UHPLC with Q-Exactive/HRMS has been increasingly used to screen and identify complex compounds in herbs and food products [8,9]. Furthermore, high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) is also a powerful tool for complex composition analysis for the quantitation and screening of specific chemicals in foods and plants [10,11,12,13]. The MS detector can provide information on molecular formula and fragmentation ions. Moreover, the multiple reaction monitoring (MRM) mode is highly specific and sensitive; it is useful for quantifying complex compounds in natural products [14].

Previous studies show that more than 10 species of the genus Panax are available around the world. Among them, Panax ginseng, Panax quinquefolius, and Panax notoginseng are the most recognized species and have been subjected to extensive study [15,16]. The other Panax species are less known. Panax japonicas (PJ), Panax japonicus var. major (PM), and Panax zingiberensis (PZ) are three different ginseng herbs with similar bioactivities; they grow in the mid- and low-latitude areas in the Northern hemisphere [17,18]. Similar to other Panax species, they contain a high amount of various chemical constituents, such as saponins, polysaccharides, amino acids and microelements, which are believed to contribute to their multiple bioactivities and restorative functions. PJ is widely used as a traditional medicine in China and Japan and has been recorded in the Chinese Pharmacopoeia and the Japanese Pharmacopoeia [17,19,20]. PM, which is thought to be a variety of PJ, has also been recorded in the Chinese Pharmacopoeia [18]. PZ is widely used for strengthening the immune response and providing cardiovascular protection in folk medicines of China and Myanmar [21]. At present, these three ginseng herbs are widely incorporated into health products and dietary supplements for their related and similar pharmacological functions. However, they display certain differences in their activities and effects. Currently, there are few studies on the quantitative and qualitative analysis of the chemical compositions and investigations on the differences between these three Panax herbs. Therefore, it is crucial to study their chemical compositions, perform a quality assessment, and investigate their differences.

In the present study, a new, rapid, and sensitive UHPLC-Q-Exactive/HRMS analysis method has been developed for the first time to comprehensively screen and identify the chemical compositions of the three ginseng herbs PJ, PM, and PZ. A sensitive and practical HPLC-ESI-MS/MS method was established to simultaneously separate and accurately determine the 16 major ginsenosides in 50 batches of the three ginseng samples. Finally, discrimination of the three Panax herbs and the important compounds were investigated using the partial least squares–discriminate analysis (PLS-DA) and orthogonal partial least squares–discriminant analysis (OPLS-DA) methods based on quantitative data.

2. Materials and Methods

2.1. Materials and Reagents

All ginseng samples are listed in Table 1. Sample materials were collected from China and Myanmar from 2015 to 2016. All samples were authenticated by one of the authors, Professor Linfang Huang, and were identified as the radices of P. japonicus C. A. Mey (PJ), P. japonicus C. A. Mey. var. major (Burk) C. Y. Wu et K. M. Feng (PM), and P. zingiberensis C. Y. Wu et K. M. Feng (PZ). The voucher specimens have been deposited at the Herbarium of the Chinese Academy of Medical Science and the Peaking Union Medicinal College.

Table 1.

The sources of roots and rhizomes of Panax japonicus var. major (PM1–PM20), Panax japonicas (PJ1–PJ20), and Panax zingiberensis (PZ1–PZ10).

No. Sample Producing Area Collection Time
1 PM-1 Hongyuan county, Sichuan province, China 2016
2 PM-2 Hongyuan county, Sichuan province, China 2016
3 PM-3 Yanyuan county, Sichuan province, China 2015
4 PM-4 Yanyuan county, Sichuan province, China 2015
5 PM-5 Wenchuan county, Sichuan province, China 2015
6 PM-6 Wenchuan county, Sichuan province, China 2015
7 PM-7 Kangding county, Sichuan province, China 2016
8 PM-8 Kangding county, Sichuan province, China 2016
9 PM-9 Kangding county, Sichuan province, China 2016
10 PM-10 Fugong county, Yunnan province, China 2015
11 PM-11 Fugong county, Yunnan province, China 2015
12 PM-12 Ludian county, Yunnan province, China 2015
13 PM-13 Ludian county, Yunnan province, China 2015
14 PM-14 Ludian county, Yunnan province, China 2015
15 PM-15 Nyingchi Prefecture, Tibet area, China 2015
16 PM-16 Nyingchi Prefecture, Tibet area, China 2015
17 PM-17 Nyingchi Prefecture, Tibet area, China 2015
18 PM-18 Nyingchi Prefecture, Tibet area, China 2015
19 PM-19 Bomi county, Tibet area, China 2015
20 PM-20 Bomi county, Tibet area, China 2015
21 PJ-1 En’shi city, Hubei province, China 2016
22 PJ-2 En’shi city, Hubei province, China 2016
23 PJ-3 En’shi city, Hubei province, China 2016
24 PJ-4 Xuan’en county, Hubei province, China 2016
25 PJ-5 Xuan’en county, Hubei province, China 2016
26 PJ-6 Leshan city, Sichuan province, China 2015
27 PJ-7 Leshan city, Sichuan province, China 2015
28 PJ-8 Meishan city, Sichuan province, China 2015
29 PJ-9 Meishan city, Sichuan province, China 2015
30 PJ-10 A’ba county, Sichuan province, China 2015
31 PJ-11 A’ba county, Sichuan province, China 2015
32 PJ-12 Ya’an City, Sichuan province, China 2015
33 PJ-13 Taibai county, Shaanxi province, China 2015
34 PJ-14 Taibai county, Shaanxi province, China 2015
35 PJ-15 Taibai county, Shaanxi province, China 2015
36 PJ-16 Taibai county, Shaanxi province, China 2015
37 PJ-17 Puer city, Yunnan province, China 2015
38 PJ-18 Puer city, Yunnan province, China 2015
39 PJ-19 Jinghong city, Yunnan province, China 2015
40 PJ-20 Wenshan county, Yunnan province, China 2015
41 PZ-1 Puer city, Yunnan province, China 2015
42 PZ-2 Puer city, Yunnan province, China 2015
43 PZ-3 Puer city, Yunnan province, China 2015
44 PZ-4 Puer city, Yunnan province, China 2015
45 PZ-5 Puer city, Yunnan province, China 2015
46 PZ-6 Puer city, Yunnan province, China 2015
47 PZ-7 Myanmar, Taung-gyi 2015
48 PZ-8 Myanmar, Taung-gyi 2015
49 PZ-9 Myanmar, Taung-gyi 2015
50 PZ-10 Myanmar, Taung-gyi 2015
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The 16 reference standards of the ginsenosides, that is, ginsenoside (G)-Rg1, G-Re, Rb1, G-Rc, G-Rb2, G-Rb3, G-Rf, G-Rd, G-Rg2, G-Rg3, G-F3, G-Rh1, G-Rh2, G-Ro, notoginsenoside (NG)-R1, and pseudoginsenoside (pseudo G)-F11, were purchased from Chengdu Must Biotechnology Co., Ltd. (Chengdu, Sichuan, China). The four reference standards of the ginsenosides, that is, G-F1, G-F2, protopanoxadiol (PPD), and protopanaxatriol (PPT), were supplied by the National Institute of Control of Pharmaceutical and Biological Products (Beijing, China). Lastly, two reference standards of chikusetsu saponin (CS), that is, CS-IV and CS-IVa, were obtained from Chengdu Chroma-Biotechnology Co., Ltd. (Sichuan, China). The chemical structures of the 16 quantitative ginsenosides are shown in Figure 1. The purities of all reference standards were higher than 98%, as confirmed by HPLC.

Figure 1.

Figure 1

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The chemical structures of the 16 reference standards.

LC-MS grade acetonitrile and methanol were obtained from Fisher Scientific (Beijing, China). De-ionized water was purified using a Milli-Q Ultra-pure water system (Millipore, Bedford, MA, USA). All other reagents and chemicals were of analytical grade and obtained from Beijing Chemical Plant Co. Ltd. (Beijing, China).

2.2. Sample Solutions Preparation

The samples of PJ, PM, and PZ were pulverized into fine powder in a grinder; 1.0 g of the powder was suspended in 25 mL of methanol and ultrasonically extracted (40 kHz, 200 W) for 30 min at 40 °C. The extracted solutions were then filtered through 0.22 μm Nylon micropore membranes and used for the UHPLC-Q-Exactive/HRMS analysis.

Furthermore, 0.1 g of the powder was suspended in 20 mL of 60% methanol and ultrasonically extracted (40 kHz, 200 W) for 45 min at 40 °C. The extracted solutions were filtered and diluted 80 times using 60% methanol. The diluted solutions were filtered through 0.22 μm Nylon micropore membranes and used for the HPLC-ESI-MS/MS analysis.

2.3. Standard Ginsenosides Solutions

Certain amounts of G-Rg1, G-Re, G-Rb1, G-Rc, G-Rb2, G-Rb3, G-Rf, G-Rd, G-Rg2, G-Rg3, G-F3, G-Rh1, G-Rh2, G-Ro, G-F1, G-F2, PPD, PPT, NG-R1, Pseudo G-F11 CS-IV, and CS-IVa were dissolved in methanol to obtain 22 reference compound stock solutions (at 1.0–5.0 mg/mL). The stock solutions were diluted with methanol, and each solution was used for studying fragmentation pathways by a UHPLC-Q-Exactive/HRMS analysis.

Furthermore, a mixed solution containing the references of G-Rg1, G-Re, G-Rb1, G-Rc, G-Rb2, G-Rb3, G-Rf, G-Rd, G-Rg2, G-Rg3, G-F3, G-Rh1, G-Ro, NG-R1, CS-IV, and CS-IVa was also prepared and serially diluted with 60% methanol–water (v/v) to obtain 16 reference solutions with different concentrations, which were used for plotting standard curves in the HPLC-ESI-MS/MS analysis.

2.4. UHPLC-Q-Exactive Orbitrap HRMS Conditions for Qualitative Analysis

UHPLC analysis was performed using an Ultimate 3000 system (Dionex, Sunnyvale, CA, USA), which is equipped with an online vacuum degasser, a quaternary pump, an autosampler, and a thermostated column compartment. An ACQUITY UPLC HSS T3, 2.1 mm × 100 mm, 1.7 μm (Waters, Milford, MA, USA) was used for chromatographic separation at 40 °C. For separation, gradient elution using aqueous formic acid 0.1% (v/v) was done for mobile phase A and acetonitrile for phase B at a flow rate of 0.3 mL/min. The following gradient was applied: 0–1 min, 0% B; 1–10 min, 0%→100% B and 10–10.1 min, 0% B. The injection volume was 2 μL, and the injection temperature was set at 15 °C.

High-Resolution Mass spectrometry was performed with a Q-Exactive Orbitrap HRMS (Thermo Fisher, Waltham, MA, USA) using a heated electrospray ionization source (HESI) for the ionization of the target compounds in the negative mode. The operating parameters were as follows: spray voltage, 3.70 KV; capillary temperature, 320 °C; sheath gas pressure, 30 psi; auxiliary gas pressure, 10 arb; auxiliary gas heater temp, 300 °C; scan modes, full MS scan (resolution 70,000); and scan range, m/z 100–1500. The data were processed using the Thermo Xcalibur 3.0 software (Thermo Finnigan, San Jose, CA, USA).

2.5. HPLC-ESI-MS/MS Conditions for Quantitative Analysis

For quantitative analysis, the separation of the multicomponents was carried out using an Agilent 1260 Infinity liquid chromatography (Agilent, Lexington, MA, USA) equipped with a quaternary pump, an online vacuum degasser, an autosampler, and a thermostatic column compartment. Chromatographic separation was performed on a Waters C18 column (3.9 mm × 150 mm, 4.6 μm). The mobile phase consisted of (A) acetonitrile and (B) a 0.05% formic acid aqueous solution by gradient elution (0–3 min, 20%→23% A; 3–8 min, 30%→35% A; 8–15 min, 35% A; 15–20 min, 35%→60% A; 20–22 min, 60%→80% A; 22–24 min, 80%→95% A; 24–25 min, 95%→20% A). The flow rate was 1 mL/min, and the split ratio was set at 3:2. The temperature was set at room temperature. The injection volume was 10 μL.

The Applied Biosystems 3200QTRAP triple quadrupole tandem mass spectrometer (Applied Biosystems/MDS Sciex, Concord, Ontario, Canada) used was equipped with an electrospray ionization (ESI) source for the mass analysis and detection. All data collected were analyzed and processed using the Analyst 1.6 software (Applied Biosystems/MDS Sciex. Foster City, CA, USA). The turbo ion spray source was set in the negative ionization mode. Multiple reaction monitoring (MRM) was used for detection transitions. The selective ion-pair, DP, and eV of the 16 saponins are shown in Table 2. The ion spray voltage was set at −4500 V, the source temperature was set at 450 °C, and gas 1 and gas 2 were set at 50 psi and 45 psi, respectively.

Table 2.

The retention time, precursor ions, product ions, and multiple reaction monitoring (MRM) parameters of the 16 analytes in the negative ion mode. Retention time (TR), declustering potential (DP), apillaryelectrophoresis (CE).

No. Analyte TR (min) Precursor Ion (m/z) Product Ion (m/z) DP/V CE/V
1 NG-R1 5.48 931.2 475.1 125 70
2 G-Rg1 6.42 799.2 637.1 100 55
3 G-Re 6.56 945.3 475.2 105 62
4 G-Rf 11.21 799.2 475.1 100 50
5 G-F3 12.09 769.2 475.1 105 55
6 G-Rg2 13.14 783.2 475.1 105 58
7 G-Rh1 13.27 637.2 475.1 75 45
8 G-Rb1 13.86 1107.2 945.1 115 65
9 G-Ro 14.68 955.1 793.0 110 60
10 G-Rc 14.72 1077.2 783.2 105 55
11 G-Rb2 15.70 1077.2 945.2 105 50
12 G-Rb3 16.01 1077.2 783.1 100 55
13 CS-IV 16.31 925.1 569.1 50 45
14 CS-IVa 17.48 793.2 569.2 35 45
15 G-Rd 17.51 945.2 621.2 105 60
16 G-Rg3 20.68 783.2 621.2 100 60
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2.6. Quantitative Method Validation

To verify linearity, the standard solutions containing 16 reference substances at seven different concentrations were injected into the triple quadrupole tandem mass spectrometer and analyzed. Calibration curves of the reference standards were constructed by plotting the integrated peak area versus the corresponding concentrations. The limit of detection (LOD) and the limit of quantification (LOQ) of the 16 ginsenosides were determined by injecting a series of standard solutions until the basis of response at the signal-to-noise ratio (S/N) was about 3 times for LOD and 10 times for LOQ. To determine precision, the samples were analyzed six times within the same day. Reproducibility was evaluated by extracting and analyzing six replicates of the same batch of sample with the established method. To determine stability, the same sample solution was analyzed at 0, 2, 4, 8, 12, and 24 h. Furthermore, a recovery test was used to evaluate the accuracy of this method. Known amounts of ginsenoside standards were added into a 0.1 g of sample six times; the six mixtures were extracted and analyzed.

2.7. Multivariate Statistical Analysis

A multivariate statistical analysis was performed using the SIMCA-P 13.0 software (Umetrics AB, Umea, Sweden) using a partial least squares–discriminant analysis (PLS-DA) and an orthogonal partial least squares–discriminant analysis (OPLS-DA). The score plots of all samples employed UV scaling. The heat map was drawn using the Heatmap illustrator 1.0 (Wuhan, Hubei, China).

3. Results and Discussion

3.1. Identity Assignment and Confirmation of the Components in PJ, PM, and PZ

In this study, the UHPLC-Q-Exactive/HRMS technique was utilized to rapidly separate and comprehensively identify the major compounds in PJ, PM, and PZ. To separate most of the compounds and achieve the most sensitive detection in a short time, the chromatographic and spectral conditions were optimized. Because the negative mode was more sensitive than the positive mode for detecting ginsenosides in the pre-experiment, heated electrospray ionization of the chemical compounds was performed in the negative ion mode. In addition, formic acid, when added to the mobile phase, not only improved the chromatographic peaks, but also easily generated formic acid adductions [M + HCOO]−, which made it easier to detect and confirm the molecular ion. After optimizing the experimental conditions, the base peak chromatograms were obtained as shown in Figure 2. The details for the identified ginsenosides, such as the retention time (tR), the molecular formula, the theoretical molecular mass, the experimental molecular mass, and MS/MS (fragment ion) information, are summarized in Table 3. These provide abundant information that can be used as a basis for identifying the constituents in the three Panax herbs. The mass error for molecular ions in all identified ginsenosides was within 10 ppm, indicating that the experimental molecular formula well-matched with the quasimolecular ions, theoretical molecular ions, and fragment ions.

Figure 2.

Figure 2

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The base peak chromatogram of the roots and rhizomes of PJ (A), PM (B), and PZ (C) in negative mode. Panax japonicas (PJ), Panax japonicus var. major (PM), Panax zingiberensis (PZ).

Table 3.

Characterization of compounds using UPLC-Q-Exactive/MS (PJ, Panax japonicas; PM, Panax japonicus var. major; PZ, Panax zingiberensis).

No. TR/min Formula [M − H]− [M + HCOO]− MS/MS Identification Sample
Calculated Measured
1 5.07 C53H88O23 1091.56327 1091.52698 1023, 1007, 965, 783 Yesanchinoside G PJ
2 5.31 C48H82O19 961.53666 961.53546 1007.54340 799, 781, 637, 619 G-Re1/G-Re2/G-Re3/NG-N/NG-M isomer PJ, PZ
3 5.36 C53H90O22 1077.58400 1077.54590 945, 783, 637, 475, 391, 191 Floral G-M/Floral G-N PJ, PM, PZ
4 5.44 C53H88O23 1091.56327 1091.52454 929, 767, 473 Yesanchinoside G isomer PJ, PM, PZ
5 5.61 C47H80O19 947.52101 947.52203 993.52789 815, 653, 579, 491, 391 Vina G-R6/Yesanchinoside C PZ
6 5.64 C48H82O19 961.53666 961.53775 1007.54224 799, 781, 637, 475, 391 20-glc-G-Rf PJ, PM
7 5.74 C48H82O19 961.53666 961.53503 1007.54285 943, 931, 799, 637 G-Re1/G-Re2/G-Re3/NG-N/NG-M isomer PJ, PM, PZ
8 5.75 C54H92O23 1107.59457 1107.59314 1153.60094 945, 783, 637, 475, 391 Yesanchinoside E PM, PZ
9 5.92 C41H70O14 785.46818 785.46246 831.47443 739, 653, 491, 391 Majonoside R2 isomer PJ
10 5.93 C48H82O19 961.53666 961.53602 1007.54651 799, 781, 637, 475, 391 20-glc-G-Rf isomer PJ
11 5.94 C53H90O22 1077.58400 1077.58337 1123.58960 945, 783, 637, 475, 391, 191 FloralG-M/Floral G-N PM
12 5.99 C41H70O14 785.46818 785.46429 831.47418 739, 653, 491, 391 Majonoside R2 isomer PJ, PZ
13 * 6.01 C47H80O18 931.52609 931.52631 977.53192 799, 769, 637, 475 NG-R1 PJ, PM, PZ
14 6.09 C42H72O14 799.48383 799.48421 667, 653, 491, 455, 391 Pseudo G-F11 isomer PJ, PM
15 6.10 C51H82O18 981.54174 981.54567 793, 763, 619, 581, 455, 371 Pseudo G-RT1 butyl ester PM
16 6.11 C56H94O24 1149.60513 1149.60181 1195.61084 1149, 1107, 961, 783, 637, 475, 391 Acetyl Yesanchinoside E PM
17 * 6.13 C48H82O18 945.54174 945.53772 991.54773 783, 637, 619, 475, 391, 205 G-Re PJ, PM, PZ
18 * 6.18 C42H72O14 799.48383 799.48541 845.48975 637, 475, 391 G-Rg1 PJ, PM, PZ
19 6.27 C45H74O17 885.48423 885.48517 845, 829, 781, 637, 619, 475, 391 Malonyl-G-Rg1 PJ, PZ
20 6.29 C58H98O26 1209.62626 1209.59033 1165, 781, 619, 459 NG-Fc PM
21 6.30 C47H80O19 947.52101 947.52191 815, 653, 579, 491, 391 Vina G-R6/Yesanchinoside C PJ, PM, PZ
22 6.32 C51H84O21 1031.54214 1031.54419 987, 945, 637, 475, 391 Malonyl G-Re PJ, PZ
23 6.34 C41H70O14 785.46818 785.46503 831.47430 739, 653, 491, 391 Majonoside R2 isomer PJ, PM, PZ
24 * 6.40 C42H72O14 799.48383 799.48566 799.47870 754, 653, 491,473, 455 Pseudo G-F11 PJ, PM
25 6.46 C48H82O19 961.53666 961.53662 1007.54055 799, 781, 637, 499 G-Re1/G-Re2/G-Re3/NG-N/NG-M isomer PJ, PM, PZ
26 6.53 C50H84O19 987.55231 987.55084 1033.55835 945, 791, 763, 637,475, 391, 275 Acetyl G-Re PM, PJ, PZ
27 6.54 C44H74O15 841.49440 841.49204 887.50067 841, 795, 637, 475, 391 Acetyl-Rg1 PJ, PZ
28 6.55 C42H72O15 815.47875 815.47961 861.48315 637 Floralquinquenoside B PJ, PM, PZ
29 6.60 C48H82O19 961.53666 961.53543 1007.54660 943, 799, 781, 457 G-Re1/G-Re2/G-Re3/NG-N/NG-M isomer PJ
30 6.67 C59H100O27 1239.63682 1239.63452 1285.64172 1107, 1059, 945, 783, 621, 459 NG-R4/NG-Fa PJ, PM, PZ
31 6.68 C56H92O25 1163.58439 1163.54858 1209.59326 1117, 955, 793, 621, 537, 459, 351 Malonyl G-Rc PM
32 6.69 C48H80O19 959.52101 959.52148 1005.54272 797, 779, 635, 617, 473, 455 NG-G PM, PZ
33 6.76 C42H72O15 815.47875 815.47610 861.48440 653, 491, 415 Floralquinquenoside D PJ, PM
34 6.79 C43H72O15 827.47875 827.47998 695, 491, 455 Vina G-R2 PZ
35 6.82 C58H98O26 1209.62626 1209.62500 1255.63147 1077, 1047, 945, 783, 621, 459 G-Ra2 PJ, PM, PZ
36 6.84 C63H106O30 1341.66852 1341.66748 1387.67493 1209, 1077, 945, 783, 621, 459 NG-Q PJ
37 6.86 C44H74O15 841.49440 841.49880 887.50098 799, 637, 475, 391 Acetyl-Rf PJ, PM, PZ
38 6.89 C59H100O27 1239.63682 1239.63538 1285.64185 1077, 1059, 945, 783, 765, 459 NG-R4/NG-Fa PJ, PM, PZ
39 * 6.92 C54H92O23 1107.59457 1107.59302 1153.59973 945, 783, 621, 459 G-Rb1 PJ, PM, PZ
40 6.95 C57H94O26 1193.59496 1193.59509 1149, 1107, 945, 783, 621, 459, 375 Malonyl G-Rb1 PJ, PM, PZ
41 * 6.96 C42H72O14 799.48383 799.48175 845.48956 637, 475, 391 G-Rf PJ, PM, PZ
42 6.97 C58H98O26 1209.62626 1209.62488 1255.63074 1077, 1047, 915, 945, 783, 621, 459 G-Ra1 PJ, PZ
43 6.99 C41H70O14 785.46818 785.46852 831.47382 653, 491 Majonoside R2 PJ, PM, PZ
44 7.00 C53H84O23 1087.53196 1087.53149 955, 925, 793, 569, 497, 455, 283 Stipuleanoside R2 PJ, PM, PZ
45 7.03 C61H100O29 1295.62665 1295.62537 1251, 1209, 1077, 945, 783, 621, 459 Malonyl G-Ra2 PJ, PZ
46 7.04 C42H72O14 799.48383 799.48041 845.48962 637, 619, 499, 457 Majoroside F2/F3/F4 PJ, PM
47 7.04 C48H76O19 955.48971 955.49017 1001.49530 793, 631, 455, 349 G-Ro isomer PJ, PM, PZ
48 * 7.05 C53H90O22 1077.58400 1077.58130 1123.58936 945, 783, 621, 459 G-Rc PM, PZ
49 7.06 C53H84O23 1087.53196 1087.53235 1133.53625 925, 731, 569, 459 Stipuleanoside R2 isomer PZ
50 7.07 C56H92O25 1163.58439 1163.58459 1119, 1077, 945, 783, 621, 459 Malonyl G-Rb2 PM
51 7.08 C57H94O26 1193.59496 1193.59497 1149, 1107, 945, 783, 621, 459, 375 Malonyl G-Rb1 isomer PJ, PM
52 * 7.09 C41H70O13 769.47327 769.47125 815.47961 637, 485, 475, 325, 311 G-F3 PJ, PM, PZ
53 7.09 C56H94O24 1149.60513 1149.60083 1195.60669 1107, 945, 783, 621, 475 Yesanchinoside F PJ, PM
54 * 7.15 C53H90O22 1077.58400 1077.58179 1123.58923 945, 915, 783, 621, 459 G-Rb2 PJ, PZ
55 * 7.16 C48H76O19 955.48971 955.48987 1001.49347 793, 731, 659,631, 455 G-Ro PJ, PM, PZ
56 7.18 C61H100O29 1295.62665 1295.62561 1107, 945, 783, 621, 459 Malonyl G-Ra1 PJ
57 7.19 C56H92O25 1163.58439 1163.58435 1119, 1077, 945, 783, 621, 459, 293 Malonyl G-Rb3 PJ, PM
58 * 7.21 C42H72O13 783.48892 783.48627 829.49475 637, 619, 475, 457, 391, 205,161 G-Rg2 PJ, PM, PZ
59 7.22 C45H74O17 885.48423 885.48474 829, 799, 637, 475 Malonyl-G-Rf PM
60 * 7.23 C53H90O22 1077.58400 1077.58289 1123.58960 945, 915, 783, 621, 459 G-Rb3 PZ
61 * 7.32 C47H74O18 925.47914 925.47894 971.48279 873, 793, 612, 569, 455 CS-IV PJ, PZ
62 * 7.35 C36H62O9 637.43101 637.42828 683.43695 457, 391, 283, 255 G-Rh1 PJ, PM, PZ
63 7.37 C48H82O19 961.53666 961.53674 1007.54553 815, 781, 499 G-Re1/G-Re2/G-Re3/NG-N/NG-M isomer PM
64 * 7.43 C48H82O18 945.54174 945.53973 991.54706 783, 621, 459 G-Rd PJ, PM, PZ
65 7.44 C51H84O21 1031.54214 1031.54248 987, 945, 783, 621, 459, 375 Malonyl G-Rd PJ, PM, PZ
66 7.46 C50H84O19 987.55231 987.55151 1033.55066 945, 783, 621, 459 Acetyl G-Rd PM, PJ
67 * 7.53 C42H66O14 793.43688 793.43701 839.44269 631, 569, 509, 497, 455 CS-IVa PJ, PM, PZ
68 7.60 C51H84O21 1031.54214 1031.54224 987, 945, 783, 621, 459, 375 Malonyl G-Rd isomer PM, PJ
69 * 7.61 C36H62O9 637.43101 637.43042 683.43707 475, 391 G-F1 PJ, PM, PZ
70 7.63 C48H82O18 945.54174 945.53990 991.54767 899, 783, 855, 793, 621, 459 Gypenoside XVII PJ, PM, PZ
71 7.64 C53H90O23 1093.57892 1093.57825 1047, 915, 783, 621, 459 Gypenoside LVI/LXVII/Floral G-P PJ, PZ
72 7.66 C49H78O19 969.50536 969.99005 1015.51208 807, 631, 537, 455, 393 G-Ro methyl ester PM, PZ
73 7.73 C47H80O17 915.53118 915.53667 961.53442 783, 621, 459, 375 NG-Fe PJ, PM, PZ
74 7.79 C38H64O10 679.44157 679.44607 633, 611, 475,391 Acety G-Rh1 PJ, PM
75 7.82 C47H80O17 915.53118 915.52783 961.53748 783, 621, 459, 375 CS-III PJ, PZ
76 7.82 C48H82O19 961.53666 961.53802 1007.53357 931, 799, 619 G-Re1/G-Re2/G-Re3/NG-N/NG-M isomer PJ, PM, PZ
77 7.90 C38H64O10 679.44157 679.44049 633, 475, 391 Acety G-F1 PJ, PM
78 7.92 C41H70O13 769.47327 769.43805 679, 637, 475, 391 Pseudo G-RT3/G-F5 PM, PZ
79 7.94 C48H82O19 961.53666 961.53735 1007.54629 915, 621, 499 G-Re1/G-Re2/G-Re3/NG-N/NG-M isomer PM, PJ, PZ
80 8.11 C43H68O14 807.45253 807.41650 853.46051 793, 631, 455 CS-IVa methyl ester PJ, PM, PZ
81 8.17 C42H66O14 793.43688 793.43787 839.44141 631, 613, 569, 455 CS-II PM, PZ
82 8.19 C47H74O18 925.47914 925.47986 793, 731, 569, 497, 455 CS-Ib PJ, PM, PZ
83 8.31 C47H74O18 925.47914 925.47998 971.48346 793, 763, 631, 455 pseudo G-RT1/Stipuleanoside R1 PJ, PM, PZ
84 8.38 C42H66O14 793.43688 793.43707 839.44318 731, 631, 613, 569, 455 Zingibroside R1 PJ, PM, PZ
85 * 8.42 C42H72O13 783.48892 783.48669 829.49506 621, 459 (20S) G-Rg3 PM
86 8.67 C41H64O13 763.42632 763.42659 809.43291 631, 613, 569, 455, 325 Pseudo G-RP1 PJ, PM
87 8.68 C42H70O12 765.47835 765.43286 603, 593, 441 G-Rk1 PJ, PM, PZ
88 * 8.71 C42H72O13 783.48892 783.48826 829.49457 621, 459 G-F2 PJ, PM, PZ
89 8.78 C42H72O13 783.48892 783.48615 829.49524 752, 599, 459 (20R)-G-Rg3 PJ, PM, PZ
90 8.89 C41H64O13 763.42632 763.42631 613, 569, 497, 455, 405 Pseudo G-RP1 isomer PJ, PM, PZ
91 8.90 C42H70O12 765.47835 765.43274 719, 673, 603, 573, 459 G-Rg5 PJ, PM, PZ
92 8.95 C42H70O11 749.48344 749.48045 617, 455 Pjs-4 PJ
93 9.11 C58H96O24 1175.62078 1175.67310 1221.67749 1159, 1095, 955, 793, 613, 569, 459 G-Ra6 PJ
94 9.64 C37H62O7 617.44118 617.44056 663.00000 455, 359 Oleanolic acid 28-O-β-D-glucopyranoside PJ, PM, PZ
95 9.71 C44H74O15 841.49440 841.49487 795, 633, 491, 471 Vina G-R1 PJ, PM, PZ
96 * 9.84 C30H52O4 475.37819 475.36335 459, 391 PPT PJ, PM, PZ
97 9.87 C36H60O7 603.42553 603.33807 649.34393 441, 279 G-Rk2 PJ, PM
98 10.08 C36H62O8 621.43610 621.43738 667.44208 459, 375, 325, 311 G-K PJ, PM
99 * 10.18 C36H62O8 621.43610 621.43530 667.44232 459, 375, 283, 255 G-Rh2 PJ, PM, PZ
100 10.34 C36H62O10 653.42592 653.42682 491 Pseudo G-RT4 PJ, PM
101 * 10.94 C30H52O3 459.38327 459.39596 375, 329 PPD PJ, PM
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* identified with a standard reference.

Phytochemistry research studies have demonstrated that the chemical constituents in the Panax genus are very complex [1,22,23]. Ginsenosides are the major effective components. Currently, hundreds of ginsenosides have been isolated and unambiguously characterized from these Panax species, especially from P. ginseng, P. quinquefolium, and P. notoginseng. Furthermore, the fragmentation pathways of numerous ginsenosides have been reported by numerous research studies [24,25], which makes it easier to detect and identify secondary metabolites from Panax species using the UHPLC-Q-Exactive/HRMS technique. In the present study, ESI-MS on negative ion mode was used for compound detection and characterization due to its high sensitivity and sensitivity, as well as clear mass spectra in the negative ion mode. A total of 101 compounds were detected and tentatively identified, including 82 from PJ, 78 from PM, and 67 from PZ. Among them, 22 ginsenosides, including ginsenosides G-Rg1, G-Re, G-Rb1, G-Rc, G-Rb2, G-Rb3, G-Rf, G-Rd, G-Rg2, G-Rg3, G-F3, G-Rh1, G-Rh2, G-Ro, G-F1, G-F2, NG-R1, pseudo G-F11, PPD, PPT, CS-IV, and CS-IVa, were unambiguously identified by comparing their retention times and fragment ions with the reference standards. The others were tentatively assigned by the empirical molecular formula, theoretical molecular mass, and MS/MS fragment ions as well as the retention sequence of isomeric ginsenosides.

In the MS spectra, most of the ginsenosides showed deprotonated ions [M − H]− and/or formic acid adduct ions [M + HCOO]− in the negative ion mode. However, it is worth noting that the malonyl-ginsenosides could not produce adduct ions [M + HCOO]− because malonyl-ginsenosides are unstable. It is easy to lose CO2 from the deprotonated molecules of these compounds under demalonylation, which results in the detection of the peaks in the quasi-molecular ions of [M − H − CO2]− and [M − H − Malonyl]−, which were found in compounds 19, 22, 31, 40, 45, 46, 50, 51, 56, 57, 59, 65, and 68. Additionally, according to the negative MS, MS/MS spectra of the ginsenosides, the deprotonated ions and their product ions exhibited the common fragmentation pattern that corresponds to the successive or simultaneous loss of glycosidic units, such as the glucosyl (Glc) group (162 Da), the rhamnosyl (Rha) group (146 Da), the xylose(Xyl)/arabinose(Ara) group (132 Da), and the glucuronyl (Glu A) group (176 Da), at the C-20, C-3, or C-6 sites until the formation of an aglycone ion. The characteristic ions at m/z 475 (C30H51O4) and m/z 459 (C30H51O3) were observed in the PPTs (such as compounds 3, 6, 8, 10, 11, 13, 17, 18, 41, 53, 62, 69, and 78 ) and PPDs (such as compounds 20, 30, 31, 35, 36, 39, 42, 48, 54, 60, 64, 70, 71, 75, 85, 88, 89, 91, 93, and 98 ), respectively. As shown in Figure 3A,B, G-Rb1 produced [(20S)-protopanaxadiol − H]− at m/z 459.38260 (C30H51O3) in the MS/MS spectrum by the successive loss of four Glc (162 Da), and NG-R1 gave the [(20S)-protopanaxatriol − H]− at m/z 475.37848 (C30H51O4) via the successive elimination of one Xyl and two Glc. Moreover, the OAs displayed an aglycone ion at m/z 455 (C30H47O3) corresponding to [oleanolic acid − H]−, which was visible for compounds 47, 55, 61, 67, 80, 81, 82, 84, and 94. Figure 3C,D show the MS/MS spectra of G-Ro (55) and CS-IV (61). These two saponins produced [oleanolic acid − H]− at m/z 455 (C30H47O3) after the successive loss of Glc, and/or Ara, and Glu A.

Figure 3.

Figure 3

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The MS/MS spectrum of ginsenoside -Rb1 (A), ginsenoside -R1 (B), ginsenoside -Ro (C), and chikusetsu saponin -IV (D).

Notably, some Octillol-type triterpenoid saponins were also detected and identified in the three ginseng herbs. For example, compounds 24 (Pseudo G-F11), 34 (Vina G-R1), 95 (Vina G-R2), 100 (Pseudo G-RT4), 5, and 21 (Vina G-R6/Yesanchinoside C) were observed at m/z 491 (C30H51O5) via the loss of a different sugar moiety, corresponding to the deprotonated ions of Octillol-type aglycone.

3.2. Validation of the Quantitative Analytical Method

The HPLC-ESI-MS/MS quantitative analysis method was validated. The regression equations, coefficient of determination, linear ranges, LODs, and LOQs for the quantitative analysis of the 16 reference ginsenosides are shown in Table 4. The calibration curves for all 16 reference substances showed good linear regression (r > 0.999) within the test ranges. The LODs of the 16 reference compounds were estimated to be 0.13–2.22 ng/mL, whereas the LOQs were 0.31–5.90 ng/mL. The precision, repeatability, stability, and recovery are listed in Table 5. The precision of the quantitative method was determined; the validation studies showed that the relative standard deviation (RSD) was less than 4.87%, and the repeatability of the method was very good (RSD < 4.93%). The RSD of the storage stability was less than 4.60% in 24 h. The recovery was in the range of 99.25–104.10% with an RSD of less than 3.45%. The established HPLC-ESI-MS/MS method was accurate and reliable and is therefore appropriate for quantitative analysis.

Table 4.

The regression equations, linear range, limit of detection (LOD), and limit of quantification (LOQ) of the 16 analytes.

No. Analyte Regression Equations Correlation Coefficients (r) Linear Range (ng × mL−1) LOD (ng × mL−1) LOQ (ng × mL−1)
1 N-R1 Y = 22.1X + 29.4 0.9991 1.56~1560 0.61 1.22
2 G-Rg1 Y = 7.7X + 193 0.9999 3.91~3910 1.91 3.81
3 G-Re Y = 18X + 103 0.9998 6.25~6250 0.38 1.22
4 G-Rf Y = 53.4X + 20 0.9998 0.78~780 0.19 0.38
5 G-F3 Y = 12.3X + 8.91 0.9997 1.17~1170 0.36 0.91
6 G-Rg2 Y = 71.7X + 50.6 0.9994 7.03~7030 0.21 0.86
7 G-Rh1 Y = 2.92X − 1.56 0.9992 6.24~1560 2.22 5.90
8 G-Rb1 Y = 7.5X − 105 0.9996 3.15~3130 1.53 3.05
9 G-Ro Y = 27.8X + 3750 0.9992 9.38~9380 0.29 0.88
10 G-Rc Y = 7.97X + 65.1 0.9998 1.56~1560 0.61 1.22
11 G-Rb2 Y = 12.3X + 78.7 0.9998 1.56~1560 0.41 1.22
12 G-Rb3 Y = 15.1X + 56.6 0.9996 1.56~1560 0.41 1.38
13 CS-IV Y = 79.3X + 2610 0.9997 6.25~6250 0.16 0.31
14 CS-IVa Y = 13.4X + 844 0.9991 7.81~7810 0.13 0.38
15 G-Rd Y = 14X + 188 0.9993 1.56~1560 0.41 1.07
16 G-Rg3 Y = 24.1X − 17.1 0.9995 0.78~780 0.25 0.76
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Table 5.

The precision, repeatability, stability, and recovery of the 16 analytes.

No. Analyte Precision (RSD, %, n = 6) Repeatability (RSD, %, n = 6) Stability (RSD, %, n = 6) Recovery
Measured (%) RSD (%)
1 N-R1 1.78 3.12 4.43 99.25 3.45
2 G-Rg1 3.23 4.93 3.93 101.21 2.45
3 G-Re 3.65 2.86 4.43 103.19 0.94
4 G-Rf 4.87 4.05 4.60 99.92 2.74
5 G-F3 4.52 4.86 3.53 100.60 3.22
6 G-Rg2 1.32 4.19 3.79 101.40 1.90
7 G-Rh1 4.72 4.11 2.09 100.22 2.68
8 G-Rb1 4.59 4.10 2.02 104.10 0.69
9 G-Ro 2.99 1.40 1.02 100.38 2.84
10 G-Rc 4.16 2.90 2.60 102.00 2.37
11 G-Rb2 3.78 3.70 4.43 102.29 2.61
12 G-Rb3 2.29 4.26 4.56 102.67 1.56
13 CS-IV 2.70 4.32 2.47 100.98 2.68
14 CS-IVa 3.18 4.74 1.67 101.55 1.89
15 G-Rd 4.21 3.34 3.72 100.73 3.14
16 G-Rg3 2.72 3.41 3.31 101.67 2.77
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RSD, relative standard deviation.

3.3. Determination of the 16 Ginsenosides Using HPLC-ESI-MS/MS

The contents of the major 16 ginsenosides from 50 batch samples were determined using the HPLC-ESI-MS/MS method, including 6 PPDs (G-Rb1, Rb2, Rb3, Rc, Rd, and Rg3), 7 PPTs (G-Re, Rf, Rg1, Rg2, Rh1, F3, and N-R1), and 3 OAs (G-Ro, CS-IV, and CS-IVa). The chromatograms obtained with reference substances and sample solutions are shown in Figure 4. The determination results are shown in Table 6 and Figure 5. In PJ, PM, and PZ, the contents of the PPDs were 4.449 ± 2.902%, 10.793 ± 6.135%, and 12.607 ± 4.247%, respectively. Among them, G-Ro, CS-IV, and CS-IVA have the highest content in plants, which is about 20–70 times that of other ginsenosides. Moreover, the content of G-Rb2, G-Rb3, G-RC, G-R3, and NG-R1 in plants is generally low, and some plants are almost undetectable. By analyzing the amount of compound, we can find that the difference in the content of these compounds (G-Rd, G-Rf, G-F3, G-Ro, and CS-IV) is larger than the others between PM and PJ. The differences in the content of NG-R1, G-Rb1, G-F3, G-Rh1, G-Re, G-Rg1, are larger than the others between PM and PZ. The differences in the content of G-Rh1, NG-R1, G-Rg1, G-F3, G-Ro, and CS-IVA between PJ and PZ are significant. In general, PJ and PM are similar, and PZ differs greatly from them.

Figure 4.

Figure 4

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The total ion MRM chromatograms of the reference standards (A) and the roots and rhizomes of Panax japonicas (B), Panax japonicus var. major (C), and Panax zingiberensis (D) obtained in negative mode by HPLC-ESI-MS/MS.

Table 6.

The contents (mg × g−1) of the 16 ginsenosides in the rhizomes of Panax japonicas (PJ), Panax japonicus var. major (PM), and Panax zingiberensis (PZ).

Batch PPD-Type Ginsenoside PPT-Type Ginsenoside OA-Type Ginsenoside TPPD TPPT TOA T
G-Rb1 G-Rb2 G-Rb3 G-Rc G-Rd G-Rg3 NG-R1 G-Rg1 G-Re G-Rf G-F3 G-Rg2 G-Rh1 G-Ro CS-IV CS-IVa
PM-1 5.104 0.240 0.221 0.037 2.320 0.053 0.039 1.888 3.328 2.816 2.480 1.424 0.298 55.200 46.240 29.760 7.976 12.273 131.200 151.448
PM-2 5.664 0.266 0.245 0.011 1.344 0.026 0.057 2.064 2.864 2.352 1.558 1.195 0.381 50.880 45.760 31.680 7.555 10.472 128.320 146.346
PM-3 4.016 0.149 0.160 0.016 0.958 - 0.041 0.786 1.984 1.744 1.302 0.925 0.159 53.920 49.440 31.584 5.300 6.941 134.944 147.185
PM-4 3.648 0.113 0.173 0.009 0.960 0.026 0.039 1.197 1.616 1.840 1.416 1.003 0.181 63.680 44.640 32.000 4.929 7.292 140.320 152.541
PM-5 5.488 0.246 0.259 0.042 1.184 0.054 0.025 1.022 2.464 2.096 1.824 1.158 0.151 61.760 41.120 43.040 7.273 8.740 145.920 161.934
PM-6 3.472 0.278 0.275 0.014 0.699 0.027 0.024 1.616 1.541 1.595 1.453 0.738 0.221 71.040 49.120 34.560 4.766 7.188 154.720 166.673
PM-7 2.944 0.109 0.158 0.009 0.765 0.056 0.089 1.726 2.080 1.515 1.320 0.483 0.162 82.080 27.520 40.960 4.040 7.375 150.560 161.975
PM-8 5.712 0.139 0.182 0.005 0.890 0.026 0.056 1.507 3.008 1.525 1.808 0.576 0.376 106.080 19.840 60.160 6.955 8.856 186.080 201.891
PM-9 3.232 0.080 0.118 0.008 0.539 - 0.078 1.352 4.096 1.603 2.624 0.392 0.317 104.800 27.840 54.240 3.977 10.462 186.880 201.319
PM-10 3.904 0.200 0.296 - 14.557 - 0.259 0.059 0.136 0.666 2.656 0.099 0.111 78.560 23.856 29.120 18.957 3.986 131.536 154.479
PM-11 4.256 0.250 0.231 - 13.240 0.067 0.291 0.026 0.166 0.518 2.688 0.013 0.130 81.600 22.338 33.440 18.044 3.832 137.378 159.253
PM-12 4.240 0.274 0.489 - 17.056 0.053 0.347 - 0.099 0.678 2.726 0.009 0.130 76.160 27.040 28.640 22.112 3.991 131.840 157.943
PM-13 4.736 0.168 0.386 - 15.824 0.026 0.293 - 0.163 0.929 3.086 0.058 - 78.880 27.200 26.400 21.140 4.530 132.480 158.150
PM-14 4.992 0.355 0.292 - 15.744 0.111 0.307 - 0.077 0.747 2.720 0.035 - 75.520 27.360 33.440 21.494 3.886 136.320 161.701
PM-15 3.296 0.255 0.296 - 5.894 - 0.235 0.421 0.714 0.208 3.936 0.451 0.062 91.200 11.360 35.680 9.741 6.027 138.240 154.008
PM-16 2.992 0.267 0.250 - 5.304 - 0.232 0.200 0.904 0.176 4.443 0.291 0.117 96.160 12.960 40.320 8.812 6.364 149.440 164.617
PM-17 2.464 0.330 0.354 - 7.968 0.040 0.206 0.331 0.387 0.136 3.376 0.205 0.090 65.120 6.128 46.080 11.155 4.732 117.328 133.215
PM-18 3.024 0.485 0.376 - 6.640 0.026 0.234 0.232 0.429 0.126 2.576 0.302 0.102 81.600 6.544 37.760 10.551 4.001 125.904 140.456
PM-19 1.984 0.354 0.224 - 6.848 0.036 0.261 0.378 0.338 0.068 3.504 0.192 0.107 75.840 5.216 30.880 9.445 4.847 111.936 126.228
PM-20 2.640 0.461 0.635 - 7.904 - 0.278 0.224 0.208 0.099 3.632 0.300 0.089 66.880 4.272 34.720 11.640 4.830 105.872 122.342
Mean 3.890 0.251 0.281 0.008 6.332 0.031 0.170 0.751 1.330 1.072 2.556 0.493 0.159 75.848 26.290 36.723 10.793 6.531 138.861 156.185
SD (n = 20) 1.110 0.110 0.122 0.012 5.925 0.029 0.116 0.722 1.277 0.851 0.926 0.437 0.109 15.590 15.537 8.686 6.135 2.544 20.353 19.814
PJ-1 1.626 0.061 - - 0.355 0.031 0.055 5.360 2.016 0.422 0.418 0.136 - 88.480 50.720 10.880 2.073 8.407 150.080 160.560
PJ-2 1.280 - - - 0.352 0.029 - 3.232 2.432 0.650 0.789 0.189 0.130 101.120 37.440 10.544 1.661 7.422 149.104 158.186
PJ-3 1.363 - - 0.010 0.432 0.054 - 2.128 1.427 1.099 0.571 0.131 0.130 70.080 39.680 8.816 1.859 5.487 118.576 125.922
PJ-4 1.280 0.009 - - 0.917 0.004 0.010 2.992 1.760 0.512 0.922 0.158 - 77.280 33.600 - 2.210 6.354 120.880 129.443
PJ-5 1.499 - 0.028 - 0.701 0.056 - 4.560 1.760 0.638 0.944 0.136 - 77.600 31.840 5.984 2.284 8.039 115.424 125.746
PJ-6 7.728 0.406 0.549 - 1.648 - 0.034 0.669 1.619 0.020 2.642 0.274 - 141.280 49.280 54.880 10.331 5.257 245.440 261.028
PJ-7 9.232 0.219 0.416 - 1.363 0.041 0.036 0.882 2.336 0.033 2.762 0.318 - 139.200 45.920 55.040 11.272 6.366 240.160 257.798
PJ-8 2.064 0.328 0.378 - 1.624 0.006 0.145 0.294 1.274 0.037 2.896 0.432 - 99.520 48.160 46.400 4.400 5.078 194.080 203.558
PJ-9 1.856 0.674 0.507 - 1.792 0.026 0.087 0.394 2.064 0.019 2.752 0.434 - 95.840 58.400 39.200 4.855 5.750 193.440 204.044
PJ-10 2.064 0.248 0.253 0.099 1.574 0.040 0.130 2.192 1.421 0.012 1.856 0.296 0.162 88.800 39.360 38.080 4.278 6.068 166.240 176.587
PJ-11 5.456 0.246 0.276 0.054 1.512 0.097 0.132 1.680 0.736 0.032 2.338 0.190 0.115 118.880 41.600 44.640 7.642 5.222 205.120 217.984
PJ-12 5.792 0.707 0.320 0.038 2.256 0.026 0.055 0.072 0.045 0.011 1.640 0.164 0.091 145.600 34.240 69.600 9.140 2.079 249.440 260.658
PJ-13 1.114 0.126 0.173 0.300 0.187 0.026 0.070 3.904 3.008 0.302 0.334 0.067 0.584 137.920 57.280 16.160 1.926 8.270 211.360 221.556
PJ-14 1.541 0.157 0.144 0.250 0.166 0.013 0.087 2.688 4.112 0.260 0.333 0.076 0.261 145.600 62.880 13.936 2.270 7.816 222.416 232.503
PJ-15 2.112 0.215 0.117 0.277 0.514 0.026 0.187 4.032 3.808 0.230 0.475 0.128 0.290 146.240 59.840 10.528 3.260 9.151 216.608 229.019
PJ-16 1.595 0.275 0.294 0.328 0.664 0.026 0.187 4.624 3.968 0.296 0.627 0.166 0.290 145.280 65.440 15.808 3.183 10.159 226.528 239.870
PJ-17 3.146 0.434 0.248 0.171 1.216 0.026 0.121 0.469 1.309 0.031 1.376 0.656 - 74.080 39.360 54.720 5.240 3.962 168.160 177.363
PJ-18 2.496 0.328 0.115 - 1.080 0.041 0.158 0.298 1.062 0.019 0.869 0.418 - 76.960 46.080 54.560 4.061 2.823 177.600 184.484
PJ-19 2.269 0.166 0.181 0.018 0.981 - 0.117 0.290 2.224 0.031 0.832 0.458 - 78.080 47.040 36.480 3.614 3.951 161.600 169.166
PJ-20 1.680 0.326 0.202 0.037 1.152 0.028 0.234 0.989 0.768 0.013 1.424 0.598 0.130 85.760 37.280 31.840 3.425 4.156 154.880 162.461
Mean 2.860 0.246 0.210 0.079 1.024 0.030 0.092 2.087 1.957 0.234 1.340 0.271 0.109 106.680 46.272 31.405 4.449 6.091 184.357 194.897
SD (n = 20) 2.310 0.203 0.168 0.116 0.597 0.022 0.069 1.730 1.093 0.299 0.898 0.173 0.152 29.528 10.162 20.349 2.902 2.143 42.448 44.410
PZ-1 9.136 0.178 0.029 0.014 0.450 0.450 3.488 24.640 10.960 0.058 10.080 2.912 3.984 93.760 25.600 11.472 10.256 56.122 130.832 197.209
PZ-2 8.128 0.161 0.053 0.020 0.453 0.331 3.760 21.760 10.128 0.079 10.112 2.992 2.880 91.520 25.760 10.944 9.146 51.711 128.224 189.082
PZ-3 8.464 0.142 0.034 0.011 0.451 0.222 3.808 20.320 8.768 0.080 9.392 2.944 2.736 86.080 25.120 10.560 9.324 48.048 121.760 179.133
PZ-4 8.256 0.071 0.053 0.020 0.515 0.328 3.888 17.040 8.736 0.050 9.712 3.376 2.160 80.960 23.840 9.744 9.244 44.962 114.544 168.750
PZ-5 8.288 0.105 0.118 0.013 0.421 0.245 3.872 16.160 9.440 0.067 11.552 3.440 1.696 84.160 23.840 12.224 9.190 46.227 120.224 175.641
PZ-6 9.296 0.213 0.007 0.015 0.541 0.290 4.768 16.160 9.376 0.095 10.480 3.344 2.720 88.640 25.600 12.224 10.361 46.943 126.464 183.768
PZ-7 10.528 0.762 0.789 0.117 0.374 0.478 3.808 22.085 14.720 0.056 5.536 0.819 5.184 99.680 22.080 11.792 13.048 52.208 133.552 198.808
PZ-8 14.720 1.378 1.286 0.197 1.168 0.371 3.568 22.402 15.808 0.039 4.786 1.619 3.008 89.920 18.240 15.120 19.120 51.229 123.280 193.629
PZ-9 15.840 0.408 0.397 0.037 0.352 0.413 5.440 22.254 15.344 0.093 10.560 2.128 3.424 118.080 28.000 9.872 17.447 59.243 155.952 232.642
PZ-10 17.120 0.272 0.507 0.144 0.496 0.390 5.792 26.244 16.960 0.048 12.688 2.352 3.952 125.600 29.440 14.816 18.930 68.036 169.856 256.821
Mean 10.978 0.369 0.327 0.059 0.522 0.352 4.219 20.907 12.024 0.066 9.490 2.593 3.174 95.840 24.752 11.877 12.607 52.473 132.469 197.548
SD (n = 10) 3.510 0.408 0.427 0.068 0.234 0.084 0.817 3.479 3.280 0.020 2.476 0.859 1.005 14.750 3.097 1.848 4.247 7.064 17.248 27.227
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TPPD, TPPT, TOA, and T represent the content of protopanaxdiol-type ginsenosides, protopanaxtriol-type ginsenosides, oleanolic acid-type ginsenosides, and total ginsenosides, respectively; “-” represents not detected; SD, standard deviation.

Figure 5.

Figure 5

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The percentage contents of the 16 ginsenosides (A, PJ; B, PM; C, PZ) and total ginsenosides (D) in the three ginseng herbs; The content difference of 16 saponins by a two-way hierarchical clustering analysis heat map (E). Ginsenoside (G)-Rg1, G-Re, G-Rb1, G-Rc, G-Rb2, G-Rb3, G-Rf, G-Rd, G-Rg2, G-Rg3, G-F3, G-Rh1, G-Ro. Notoginsenoside (N)-R1 and chikusetsu saponin (CS) -IV and CS-Iva.

The contents of PPTs were 6.091 ± 2.143%, 6.531 ± 2.544%, and 52.473 ± 7.064%. The contents of OAs were 184.357 ± 42.448%, 138.861 ± 20.353%, and 132.469 ± 17.248%. The contents of total ginsenosides were 194.897 ± 44.410%, 156.185 ± 19.814%, and 197.548 ± 27.227%, respectively. Notably, PZ has a higher level of PPTs content than PJ and PM (by more than 8 times). In addition, G-Ro, CS-IV, and CS-IVa were the three major ginsenosides in PJ and PM, whereas G-Ro, CS-IV, and G-Rg1 were the three major ginsenosides in PZ. Different types of ginsenosides possessed different pharmacological activities. Based on the results, all three drugs clearly contained a large number of OAs and a small amount of dammarane ginsenosides, especially PJ and PM. Furthermore, the content of ginsenosides differed greatly between the three drugs, which may be the reason for their differences in clinical application.

3.4. Discrimination of PJ, PM, and PZ by a Multivariate Statistical Analysis

The variations in the 16 major compounds among the three ginseng species were intuitively represented by a two-way hierarchical clustering analysis heat map. As shown in the heat map in Figure 5E, PZ could be clearly distinguished from PJ and PM by a hierarchical clustering analysis. In contrast, PJ and PZ were not well-discriminated, and their ginsenoside contents were much closer than that of PZ.

In order to further reveal differences in the chemical composition among PJ, PM, and PZ, PLS-DA and OPLS-DA were also utilized to distinguish between different ginseng species. A total of 50 ginseng samples (20 batches of PJ; 20 batches of PM; 10 batches of PZ) were analyzed. Among them, 35 samples were randomly selected as the training set, and 15 were the prediction set. The result is shown in Figure 6. The established PLS-DA model showed good fitness (R2X = 0.699, R2Y = 0.897) and predictability (Q2 = 0.85). The PLS-DA score plot displayed that the three clusters representing the PJ, PM, and PZ groups were well-segregated, thereby indicating the remarkable differences of ginsenosides among these three Panax herbs. A chance permutation test suggested that the model was not over-fitted (as shown in Figure 6A-3). All samples in the prediction set are correctly identified, so the PLS-DA model has a classification accuracy of 100%. The VIP (variable importance in the projection) plot was used to find the important compounds. When the VIP cutoff was set at 1.0, nine important compounds for discriminating between PJ, PM, and PZ were discovered. G-Rf, G-F3, and CS-IV have the highest contribution that can distinguish the above three herbs (as shown in Figure 6A-4).

Figure 6.

Figure 6

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The PLS-DA (partial least squares–discriminate analysis) score scatter plot (A-1), the loading scatter plot (A-2), the chance permutation test to validate the occurrence or absence of over-fitting of the PLS-DA (partial least squares–discriminate analysis) model (A-3), the VIP (variable importance in the projection) values of the 16 saponins (A-4), the OPLS-DA (orthogonal partial least squares–discriminant analysis) score scatter plot based on a pairwise comparison (B-1, C-1, D-1), and the VIP values of the 16 saponins (B-2, C-2, D-2).

The result of the OPLS-DA analysis based on pairwise comparison methods is shown in Figure 6B–D. The figure reveals that samples from the same species were tightly clustered together and that different species groups were discriminated from one another by the OPLS-DA score plot. Among those with a VIP value exceeding 1.0, seven important compounds for the discrimination between PJ and PM (in order of CS-IV, G-Rf, G-F3, G-Rd, G-Ro, G-Rb1, and G-Rg1), nine for PM and PZ (in order of G-Rh1, N-R1, G-F3, G-Rb1, CS-IVa, G-Rg1, G-Re, G-Rg3, and G-Rf), and nine for PJ and PZ (in order of G-Rh1, N-R1, G-Rg2, G-F3, G-Rg3, G-Rg1, G-Rb1, G-Re, and CS-IV) were obtained.

In Chinese folk medicine, PJ and PM are historically and generally used as a herbal medicine for similar indications. These two herbs possess combined medicinal effects, which are P. ginseng’s “conserving vitality” activities and P. notoginseng’s “replenishing blood” activities [10]. However, PJ and PM are considered to be two different herbal medicines, and are recorded as “zhujieshen” and “zhuzishen” in the Chinese Pharmacopoeia, respectively. Thus, investigation on the difference in their chemical constituents and biopharmalogical effects is necessary and crucial. In our qualitative and quantitative analyses based on an LC-MS technique, PLS-DA and OPLS-DA clearly distinguished between the two herbs, even though they are very similar in composition. Furthermore, the average content of total ginsenosides in PJ was conspicuously higher than that in PM, even though PM’s content in PPDs and PPTs was more abundant. These chemical differences may contribute to the differences in clinical application.

PZ, commonly known as ginger ginseng or Myanmar ginseng, is indigenous to Yunnan province in the Southwest of China [13], and has also been reported to wildly grow at the Par Moe Ne Water Spring area in Taung-gyi, Shan State, Myanmar, which has an altitude of 1500 m above sea level. Few previous studies have focused on the comprehensive chemical compositions and determination of ginsenosides in PZ [26]. In the present study, for the first time, the chemical compositions of this herb were screened and identified by UHPLC-Q-Exactive/HRMS, and the content of 16 major ginsenosides was determined. These results are beneficial for the development and quality assessment of PZ.

In conclusion, an integrated strategy to comprehensively identify the chemical composition and simultaneously quantify 16 ginsenodsies in the three Panax herbs was successfully established. After optimization of the conditions, a total of 101 ginsenosides were detected and tentatively identified using UHPLC-Q-Exactive/HRMS, including 82 from PJ, 78 from PM, and 67 from PZ. Among these compounds, 22 were unambiguously confirmed by comparing their retention times and mass spectra with those of reference ginsenosides. The quantitative analysis was implemented using a reliable and practical HPLC-ESI-MS/MS method using MRM mode. The validation of the methodology showed favorable levels of LOD, LOQ, linearity, precision, repeatability, stability, and recovery. Finally, the PLS-DA and OPLS-DA results, based on the quantitative data, displayed a significant difference in ginsenoside content between the three ginseng-drugs. G-Rf, G-F3, and CS-IV were the three most characteristic components that can distinguish between the three herbs. The integrated LC-MS-based strategy combined with a multivariate data analysis could not only achieve a rapid, accurate, and comprehensive qualitative and quantitative analysis of the complex ginsenoside but also enable us to discriminate between PJ, PM, and PZ, which provides valuable references for the quality assessment and control of traditional Chinese medicines (TCMs).

Author Contributions

Z.D. and J.L. designed the study. Z.D., J.L., X.Z. processed the data, performed the analyses and analyzed the results, and wrote the manuscript. J.P., L.H., Z.D., J.L., X.Z. edited the manuscript. All authors read and approved the final version of the manuscript.

Funding

The work was supported by grants from the National Natural Science Foundation of China (No. 81274013, No. 81473315), the CAMS Innovation Fund for Medical Sciences (CIFMS) (No. 2016-I2M-3-015), the Key Projects in the National Science and Technology Pillar Program (NO. 2011BAI07B08).

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

Sample Availability: Samples of the compounds are not available from the authors.

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