Determination of quercitrin, the inherent component of TH
Ten microliters each of the quercitrin reference and sample solutions was precisely drawn and injected into the HPLC system under the conditions specified previously herein, and the chromatogram was recorded (Fig. 1). The HPLC results showed that the baseline separation of quercitrin with symmetric peaks and a high degree of separation could be achieved, indicating that the adopted test method had high specificity.
Investigation of the linear relationship
The quercitrin reference solution was diluted with methanol to obtain working solutions with concentrations of 6.34, 12.68, 25.36, 126.80, 317.00, and 634.00 mg/L. Ten microliters of each working solution was injected into the HPLC system for the measurement of peak areas, and regression analysis was performed by plotting the peak area against the quercitrin concentration. The regression equation obtained was Y = 2.64 × 107X + 4947.87, with R2 = 0.9999 within the concentration range of 6.34–634.00 mg/L, which indicates a good linear relationship between the quercitrin concentration and peak area.
Precision test
The quercitrin reference solution was precisely drawn, and six consecutive samples were injected into the HPLC system. The relative standard deviation (RSD) of the calculated peak areas was 0.18%, which fulfilled the requirements for quantitative analysis stipulated by the Chinese Pharmacopoeia.
Stability test
Powdered samples (0.5 g) of Taxilli Herba parasitizing mulberry (THM) were precisely weighed and used to prepare sample solutions. Quercitrin content in the sample solutions was measured by HPLC at 5-h intervals for a total duration of 24 h. The calculated RSD was 0.89%, which indicates that the quercitrin content in the sample solutions remained stable within 24 h.
Reproducibility test
Six portions of THM, each weighing 0.50 g, were precisely weighed and used to prepare TH sample solutions. Quercitrin content in the sample solutions was measured by HPLC under the conditions described in Sect. 2.4.3. The calculated RSD was 0.64%, which indicates that the adopted test method provided good reproducibility.
Sample recovery test
Six portions of THM-1 powder with known quercitrin content (2.29 mg/g) were precisely weighed, and then 567.00 µg of the quercitrin reference was precisely measured and added to each portion. Sample solutions were prepared and injected into the HPLC system to calculate the quercitrin content from the peak area. The results indicated an average quercitrin recovery rate of 99.51% and an RSD value of 2.86% (Table 5), demonstrating the reproducibility of the test method.
Table 5
Test results of quercitrin addition and recovery in Sample No. 1 (n = 6).
No. | Original amount (µg) | Additional amount (µg) | Measured quantity (µg) | Recovery rate (%) | Average recovery rate(%) | RSD (%) |
1 | 567.28 | 567.00 | 1161.88 | 104.87 | 99.51 | 2.86 |
2 | 568.79 | 567.00 | 1121.88 | 97.55 |
3 | 578.10 | 567.00 | 1143.69 | 99.75 |
4 | 571.83 | 567.00 | 1137.55 | 99.77 |
5 | 570.66 | 567.00 | 1122.41 | 97.31 |
6 | 575.41 | 567.00 | 1129.90 | 97.79 |
Measurement of quercitrin content
The powdered TH samples and powdered host tree samples were used to prepare the sample solutions The quercitrin content in various sample solutions was measured by HPLC. As shown in Table 6, TH hosted by mulberry, willow, and cinnamon all contained quercitrin, but the twigs of all hosts did not. Therefore, it could be deduced that quercitrin is an inherent component of the TH samples and that the quercitrin content of TH hosted by the different trees might affect the quality of TH.
Table 6
Contents of quercitrin in Taxilli Herba and its host plant. Items indicated by different lowercases in each column are significantly different (determined by Tukey HSD test, p < 0.05, means ± SD, n = 10)
Sample name | Content (mg/g) |
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | mean ± SD |
THM | 2.29 | 1.98 | 2.10 | 2.16 | 2.64 | 2.77 | 2.10 | 2.82 | 2.33 | 3.11 | 2.43 ± 0.38ab |
THW | 3.00 | 3.00 | 2.81 | 2.36 | 2.15 | 2.47 | 5.03 | 2.45 | 2.94 | 2.91 | 2.91 ± 0.80a |
THC | 2.25 | 1.94 | 2.33 | 1.82 | 1.46 | 1.79 | 1.95 | 2.92 | 1.89 | 2.25 | 2.06 ± 0.40b |
MB | - | - | - | - | - | - | - | - | - | - | - |
WB | - | - | - | - | - | - | - | - | - | - | - |
CB | - | - | - | - | - | - | - | - | - | - | - |
Note: “-” means not detected. |
Measurement of characteristic component contents in TH host samples
Ten microliters each of morusin, salicin, or cinnamaldehyde reference solutions and the sample solutions of TH hosted by mulberry, willow, and cinnamon was precisely drawn and injected into the HPLC system. The chromatograms were then recorded (Figs. 2–4). The HPLC results showed that the baseline separation of morusin, salicin, and cinnamaldehyde could be achieved, with symmetric peaks and a high degree of separation, indicating that the adopted method had high specificity.
Investigation of linear relationships
Morusin, salicin, and cinnamaldehyde reference solutions were diluted with methanol to obtain working solutions of the following concentrations: 0.10, 0.25, 0.42, 0.84, 1.68, and 3.36 µg/mL (morusin); 0.12, 0.24, 0.62, 1.24, 3.12, and 6.24 µg/mL (salicin); 0.96, 1.92, 3.84, 5.76, 7.68, and 9.60 µg/mL (cinnamaldehyde). Ten microliters of each working solution was injected into the HPLC system to measure the peak area, and regression analysis was performed by plotting peak area against concentration. Table 7 shows the obtained regression equations and linear ranges of morusin, salicin, and cinnamaldehyde.
Table 7
Regression equations and linear ranges of morusin, salicin and cinnamaldehyde
Components | Regression equation | R2 | Linearity (µg/mL) |
morusin | y = 3.01 × 106x-112.85 | 0.9999 | 0.10 ~ 3.36 |
salicin | y = 1.63 × 104x + 8.64 | 0.9999 | 0.12 ~ 6.24 |
cinnamaldehyde | y = 9.62 × 107x-2765.73 | 0.9999 | 0.96 ~ 9.60 |
Precision test
Morusin, salicin, and cinnamaldehyde reference solutions were used for five consecutive injections of 10 µL each into the HPLC system to measure the peak areas and calculate the content of each component. The respective RSD values of morusin, salicin, and cinnamaldehyde were 0.85%, 2.83%, and 0.11%; these are indicative of high instrument precision.
Stability test
The contents of the sample solutions were tested at 0, 1, 2, 4, 6, 12, and 24 h. The respective RSD values of morusin, salicin, and cinnamaldehyde were 1.75%, 2.71%, and 2.51%, which indicate that the samples remained stable within 24 h.
Reproducibility test
Six portions of each TH sample obtained from mulberry, willow, and cinnamon trees were precisely weighed and used to prepare sample solutions. The solutions (10 µL) were then injected into the HPLC system to measure peak areas and calculate the content of each component. The average content and RSD values were 3.06 µg/g and 2.86% for morusin, 522.26 µg/g and 2.72% for salicin, and 117.13 µg/g and 2.44% for cinnamaldehyde, respectively, indicating that the adopted method presented good reproducibility.
Sample recovery test
Six portions of each TH sample of known concentrations (3.06 µg/g morusin, 522.26 µg/g salicin, and 117.13 µg/g cinnamaldehyde) were precisely weighed. Morusin (0.77 µg), salicin (130.00 µg), and cinnamaldehyde (20.00 µg) were used to prepare sample solutions. Each solution was injected into the HPLC system using an injection volume of 10 µL. The results indicated that morusin, salicin, and cinnamaldehyde had a recovery rate of 94.84%, 95.72%, and 97.85% and RSD value of 2.17%, 1.28%, and 2.37%, respectively, as shown in Table 8.
Table 8
Recovery test of morusin, salicin, and cinnamaldehyde
Sample | Original amount (µg /g) | Additional amount (µg /g) | Measured quantity (µg /g) | Recovery rate (%) | Average recovery rate(%) | RSD (%) |
morusin | 0.77 | 0.77 | 1.49 | 93.59 | 94.84 | 2.17 |
0.78 | 0.77 | 1.51 | 96.21 |
0.75 | 0.77 | 1.48 | 96.08 |
0.73 | 0.77 | 1.43 | 91.24 |
0.79 | 0.77 | 1.52 | 96.60 |
0.78 | 0.77 | 1.51 | 95.29 |
salicin | 29.16 | 20.00 | 48.04 | 94.41 | 95.72 | 1.28 |
28.66 | 20.00 | 47.95 | 96.46 |
29.78 | 20.00 | 49.04 | 96.33 |
30.23 | 20.00 | 49.26 | 95.15 |
29.56 | 20.00 | 49.05 | 97.47 |
28.32 | 20.00 | 47.22 | 94.51 |
Cinnamaldehyde | 130.00 | 130.00 | 256.12 | 97.02 | 97.85 | 2.37 |
128.13 | 130.00 | 254.21 | 96.99 |
132.14 | 130.00 | 262.22 | 100.06 |
135.45 | 130.00 | 261.01 | 96.59 |
125.36 | 130.00 | 257.02 | 101.28 |
132.32 | 130.00 | 256.02 | 95.15 |
Measurement of morusin, salicin, and cinnamaldehyde content
Each sample (0.5 g) was precisely weighed and used to prepare sample solutions. The sample solutions were injected into the HPLC system to measure the content of each component. The result is shown in Figs. 4–6, indicated the presence of morusin and the absence of salicin and cinnamaldehyde in TH hosted by mulberry, the presence of salicin and the absence of morusin and cinnamaldehyde in TH hosted by willow, and the presence of cinnamaldehyde and the absence of morusin and salicin in TH hosted by cinnamon. These results confirm that morusin, salicin, and cinnamaldehyde are the respective characteristic components of mulberry, willow, and cinnamon and that morusin, salicin, and cinnamaldehyde components in TH were transferred from the corresponding host trees. The contents of morusin, salicin, and cinnamaldehyde in mulberry, willow, and cinnamon twigs were 134.78–437.60, 1787.91-2564.65 and 7219.36-10783.21 µg/g respectively, and the corresponding values in TH obtained from mulberry, willow, and cinnamon were 0.27–4.27、102.62-545.83 and 11.33-120.97 µg/g, respectively.