Abstract
An inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma atomic emission spectrometry (ICP-AES) was developed to determine 19 elements in safflower, a traditional Chinese medicinal herb from Xinjiang Autonomous Region and Henan Province of China. Totally 19 elements in safflower included heavy metals, i. e. As, Cd, Cu, Hg and Pb, and wholesome elements, i. e. Al, Ca, Co, Cr, Fe, Mg, Mn, Mo, Ni, P, Se, Sr, V and Zn. The results showed that the concentrations of heavy metals in safflower samples were both low, all of which met the national hygiene standards except for Pb in Xinjiang sample. Meanwhile, the distribution tendency of elements in the two samples was similar, which indicated that the plant might absorb given elements in a proportional way. The method can be used for the quality control of elements in safflower, and it provides a way for the determination of the contents of safflower from Xinjiang and Henan.
Keywords: inductively coupled plasma mass spectrometry, inductively coupled plasma atomic emission spectrometry, wholesome elements, heavy metals, safflower
1. Introduction
The use of herbal medicine, also called traditional Chinese medicine (TCM) in China, is very common in the Oriental culture. This form of complementary and alternative medicine has been around for more than 3000 years. In the Chinese culture, many medicinal materials and health products were used. For example, safflower (Carthamus tinctorius L.) is an annual, broad leaf oil seed and medicinal crop which belongs to the. family Compositae [1]. It is widely cultivated in agricultural production system of Asia, Europe, Australia and the America as a source of highquality vegetable and industrial oil [2]. It has long been used as a food colorant, dye, and herbal medicine in Oriental countries [3]. Safflower edible oil cultivars have the highest quantity of polyunsaturated fatty acids. It is also used as a feed for livestock [4]. Safflower seeds have long been clinically used in Korea as herbal medicine to promote bone formation and prevent osteoporosis. There are some reports about anti-oxidative compounds from safflower describing their activity in scavenging free radical species [5]. It is also reported that the major antioxidants in safflower seed, serotonin derivatives, may inhibit low-density lipoprotein (LDL) oxidation and atherosclerosis in apolipoprotein E-deficient mice [6], [7], [8], [9], [10].
Because of the increasing interest in traditional Chinese medicinal products such as safflower, it is important to determine whether they are safe for consumption. Levels of toxic elements such as As, Cu, Cd, Hg and Pb in the plant samples must be determined. The levels of toxic elements are usually at the μg/mL level, thus necessitating the use of ICP-MS for their determination [11, 12]. ICP-MS offers the advantages of high sensitivity and simultaneous multielement analysis capability. Furthermore, some common elements such as K, Na and P are essential for health and the quantification of these elements is important for nutritional purposes. Since the concentrations of these elements are usually at the percentage level, the use of ICP-AES is an appropriate choice for their determination because no further dilution of the sample solution is needed [13, 14]
In this work, the capability of ICP-MS/ICP-AES for the quantification of the levels of heavy metals and wholesome elements in safflower was evaluated. ICP-MS was used to determine several heavy metals and lower levels of elements, i. e. As, Cd, Cu, Hg, Pb, AI, Co, Cr, Mn, Mo, Ni, Se, V,and Zn, while ICP-AES was used to measure the higher concentration of elements, i.e. Ca, Fe, Mg, P, and Sr. This method was then applied to the analysis of safflower from Xinjiang Autonomous Region and Henan Province. And the differences between region and content of elements were also investigated, thereby providing basis for typical analysis of elements and offering a way to study the relationship between the elements and the actions of TCM.
2. Experimental
2.1. Materials and reagents
HNO3 (BV- III) was purchased from Beijing Institute of Chemical Reagents. HCIO4 was obtained from G. R. Tianjin Eastern Chemical Plant. Ultra-pure water with conductivity of 5.5 × 10−6 S/m was measured on conductometer model DOS-11A(Shuangfeng Equipment Factory, Beijing). Mixed standard solution was prepared by diluting 1000 μg/mL standard solution of different elements. Stock buffer was purchased from the National Research Center for Certified Reference Material.
2.2. Instrumentation
The analysis was made on Perkin-Elmer Sciex Elan 5000 ICP-MS and ICP-AES (Beijing Kechuang Haiguang Instrument Company). Type 800 centrifuge was from Shanghai Operation Instrument Company, and 50 W ultrasonicator was from Peking University Apparatus Factory.
2.3. Preparation of samples
Safflower was from two different regions including No.1 Xinjiang and No.2 Henan. The samples were ground and sieved to obtain particles less than 0.25 mm in diameter. They were dried for 6 h at 60°C before use. About 0.20 g dried samples were weighed and digested with 5 mL HNQ and HCIO4 (20:1, v/v). After complete digestion and removal of acid, the samples were adjusted to 5 mL with pure water, ready for measurement.
Sample solution was measured by ICP-MS/ICP-AES. The parameters for ICP-MS were forward power 1000 W, nebulizer gas flow rate 0.8 Umin, and sampling depth 10 mm; the parameters for ICP-AES were forward power 1150 W, nebulizer pressure 0.5 psi, flow capacity of auxiliary gas 1.0 Umin, and lifting capacity of pump 1.2 mUmin.
3. Results and discussion
3.1. Linearity, detection limits and accuracy
To determine the linearity of the response versus concentration for the elements, a series of mixed standard solutions at the concentrations from 0.00755 to 99.98 ng/mL(ICP-MS) and 0.05 to 5 μg/mL (ICP-AES) were tested, respectively. The results of regression analysis on calibration curves are presented in Tables 1 and 2. As can be seen, for all the analyzed elements, the correlation coefficient of the calibration curves was no less than 0.9938.
Table 1.
Results of regression analysis on calibration curves by ICPMS
| Element | Regression equation | Correlation coefficient | Linear range(ng/mL) |
|---|---|---|---|
| As | y = 0.6117x−0.0206 | 0.9994 | 0.50–10.14 |
| Cd | y = 0.564x + 0.104 | 0.9974 | 0.10–9.73 |
| Cu | y = 0.3951x + 0.005 | 0.9994 | 0.10–19.97 |
| Hg | y = 1.5918x−0.0086 | 0.9938 | 0.00755–0.21000 |
| Pb | y = 4.6763x + 0.9911 | 0.9962 | 0.10–9.67 |
| AI | y = 3.06x + 0.4275 | 0.9967 | 0.50–10.60 |
| Co | y = 4.4889x + 0.9861 | 0.9955 | 0.10–9.64 |
| Cr | y = 2.2035x + 0.0766 | 0.9998 | 0.10–9.97 |
| Mn | Y = 3.2389x + 0.2565 | 0.9997 | 0.10–9.91 |
| Mo | y = 0.8166x + 0.1544 | 0.9969 | 0.10–9.70 |
| Ni | Y = 0.9929x + 0.1884 | 0.9968 | 0.10–9.69 |
| Se | y = 0.068x−0.0048 | 0.9985 | 0.50–10.23 |
| V | y = 0.1078x−0.0006 | 0.9992 | 0.10–10.13 |
| Zn | y = 0.0994x−0.0061 | 0.9996 | 0.10–99.98 |
Table 2.
Results of regression analysis on calibration curves by ICPAES
| Element | Regression equation | Correlation coefficient | Linear range (μg/mL) |
|---|---|---|---|
| Ca | y = 2947.8x + 0.9335 | 0.9995 | 0.1–5.0 |
| Fe | y = 3485.8x + 18.943 | 0.9998 | 0.1–5.0 |
| Mg | y = 99539x + 465.25 | 0.9997 | 0.1–5.0 |
| P | y = 324x−1.8124 | 0.9999 | 0.1–5.0 |
| Sr | y = 234342x + 653.88 | 0.9996 | 0.05–2.00 |
The detection limits for the 19 elements by ICP-MS and ICP-AES methods ranged from 0.001 to 20.8 ng/mL (Tables 3 and 4). The accuracy of both the ICP-MS and ICP-AES methods was evaluated by calibrating both instruments with a blank and the standards. The accuracy range was defined as the concentration for which the results (in concentration units) were within ± 10% of the true value (designated value). The results are listed in Tables 3 and 4 for the ICP-MS and ICP-AES, respectively. As shown in Tables 3 and 4, the recoveries for most elements were between 90% and 110%, and the relative standard deviations (RSDs) were less than 5.25% for most of the samples. The recoveries and RSDs listed were acceptable.
Table 3.
Detection limit and accuracy by ICP-MS
| Element | Detection limit (ng/mL) | Recovery (n =5, %) | RSD (%) |
|---|---|---|---|
| As | 0.021 | 99.90 ± 4.37 | 4.37 |
| Cd | 0.003 | 104.70 ± 2.15 | 2.05 |
| Cu | 3.750 | 99.50 ± 2.44 | 2.45 |
| Hg | 0.024 | 94.00 ± 2.97 | 3.16 |
| Pb | 0.120 | 103.80 ± 1.66 | 1.60 |
| AI | 20.800 | 103.60 ± 5.44 | 5.25 |
| Co | 0.001 | 104.60 ± 2.33 | 2.23 |
| Cr | 0.002 | 101.60 ± 2.40 | 2.36 |
| Mn | 0.500 | 102.10 ± 0.83 | 0.81 |
| Mo | 0.002 | 103.40 ± 4.98 | 4.82 |
| Ni | 0.005 | 103.60 ± 2.36 | 2.28 |
| Se | 0.050 | 100.40 ± 5.19 | 5.17 |
| V | 0.002 | 107.50 ± 2.45 | 2.28 |
| Zn | 0.470 | 101.00 ± 2.07 | 2.05 |
Table 4.
Detection limit and accuracy by ICP-AES
| Element | Detection limit (ng/mL) | Recovery (n =5, %) | RSD (%) |
|---|---|---|---|
| Ca | 6.18 | 99.80 ± 1.12 | 1.12 |
| Fe | 1.33 | 99.60 ± 1.20 | 1.20 |
| Mg | 0.88 | 100.20 ± 0.76 | 0.76 |
| P | 6.64 | 98.90 ± 0.09 | 0.09 |
| Sr | 0.40 | 101.00 ± 0.10 | 0.10 |
3.2. Contents of the elements
To determine elements in safflower samples, ICP-MS/ICP-AES techniques were applied. ICP-MS performed multielemental analysis with an excellent sensitivity and high sample throughput. ICP-MS made it possible to determine elements (As, Cd, Cu, Hg, Pb, Al, Co, Cr, Mn, Mo, Ni, Se, V and Zn) with high precision and accuracy. Meanwhile, the use of ICP-AES is an appropriate choice for the determination of elements (Ca, Fe, Mg, P, and Sr) with the concentrations usually at the percentage level because no further dilution of the sample solution is needed.
The contents of the elements are listed in Table 5. The results showed that the two safflower samples both contained many wholesome elements (Al, Ca, Co, Cr, Fe, Mg, Mn, Mo, Ni, P, Se, Sr, V, and Zn) which are necessary to human health, and the concentrations ranged from 0.2 to 12484. 75 μg/g. Ca, Mg and P are the top three elements in the samples. Apart from the wholesome elements, the contents of heavy metals (As, Cd, Cu, Hg and Pb) are also the important quality standard of the plant. The results showed that the concentrations of heavy metals in safflower samples were low, all of which met the national hygiene standards except for Pb in Xinjiang sample [15].
Table 5.
Contents of the 19 elements in safflower from Xinjiang and Henan
| Element | Content (μg/g) |
|
|---|---|---|
| Xinjiang | Henan | |
| As | 0.51 ± 0.02 | 0.81 ± 0.02 |
| Cd | 0.089 ± 0.002 | 0.072 ± 0.001 |
| Cu | 15.26± 0.37 | 13.63 ± 0.33 |
| Hg | 0.046 ± 0.001 | 0.085 ± 0.002 |
| Pb | 5.06 ± 0.08 | ND |
| AI | 565.70 ± 29.70 | 808.63 ± 42.45 |
| Ca | 6881.10 ± 77.07 | 2484.75 ± 139.83 |
| Co | 0.34± 0.01 | 0.54 ± 0.01 |
| Cr | 1.65 ± 0.04 | 1.58 ± 0.04 |
| Fe | 940.76 ± 11.30 | 1663.52 ± 19.96 |
| Mg | 1838.65 ± 13.97 | 2975.58 ± 22.61 |
| Mn | 37.87±0.31 | 64.68 ± 0.52 |
| Mo | 0.64± 0.03 | 0.60 ± 0.03 |
| Ni | 1.31 ± 0.03 | 1.77 ± 0.04 |
| P | 1767.57 ± 1.59 | 1994.76 ± 1.80 |
| Se | 0.43 ± 0.02 | 0.20 ± 0.01 |
| Sr | 101.23 ± 0.10 | 108.43 ± 0.11 |
| V | 1.70 ± 0.04 | 3.12 ± 0.07 |
| Zn | 30.90 ± 0.63 | 26.49 ± 0.54 |
ND, not detected.
By comparing the total contents of the 19 elements in two safflower samples from Xinjiang and Henan, we found that the contents of some elements varied largely. For example, the content of Ca in safflower from Xinjiang was 6881. 1 μg/g while that from Henan was 12484. 75 μg/g. However, the difference for some elements was not so marked. For example, the content of Sr was 101. 23 μg/g in the sample from Xinjiang and 108.43 μg/g in that from Henan. The contents of 10 wholesome elements (Al, Ca, Co, Fe, Mg, Mn, Ni, P, Sr, and V) in safflower sample from Henan were higher than those from Xinjiang, whereas the contents of 4 wholesome elements (Cr, Mo, Se, and Zn) in safflower sample from Henan were lower than those from Xinjiang. The results showed that the contents of elements in safflower from Xinjiang and Henan were probably related to its growth environment. This conclusion was confirmed by other studies on TCM [16]. Furthermore, although there were differences in element concentration from one element to another, we found some interesting distribution tendencies. The concentrations of elements in the samples were seen to decrease in the following order: Ca>Mg>P>Fe>Al>Sr>Mn>Zn>V>Ni/Cr>Mo>Se/Co. The results suggest that the elements in the plant have an interdependent relationship. In another words, the plant might absorb given elements in a proportional way [17]. If this is true, an elemental fingerprint for each given plant could be found.
4. Conclusion
The proposed ICP-MS/ICP-AES has been proved to be a quick and sensitive method for the detection of various elements in the Chinese medicinal plant safflower. Methodologies were developed using ICP-MS to determine low level species while methodologies for ICP-AES were used to determine elements present at higher levels. The results showed that the two safflower samples both contained many elements (Al, Ca, Co, Cr, Fe, Mg, Mn, Mo, Ni, P, Se, Sr, V and Zn) which are necessary to human health, and the concentrations ranged from 0.2 to 12484.75 μg/g. Ca, Mg, and P are the top three elements in the samples. Besides the wholesome elements, the contents of heavy metals (As, Cd, Cu, Hg and Pb) are also the important standard to identify the quality of the plant. The results showed that the concentrations of heavy metals in safflower samples were both low, all of which met the national hygiene standards except for Pb in Xinjiang sample. By comparing the total contents of the 19 elements in two safflower sampies, we found that the distribution tendency of elements in the two samples was similar, indicating that the plant might absorb given elements in a proportional way.
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