Toxic Metals in Traditional Chinese Medicine Determination

Toxic Metals in Traditional Chinese Medicine DeterminationDetermination of cyanogenetic metals in Traditional Chinese Medicine samples by atomic liberation spectrometryTraditional Chinese Medicines(TCM) pay back gained increasing trouble worldwide because of their effectiveness and small side effects1. The excess of toxic metals in these medicines have become superstar of the biggest problems that affected their export and hinde flushed their introduction to the world2. In recent years, many domestic and abroad testing organizations paid great attention to the toxic metals in handed-down Chinese medicines. everydayly, toxic metals in traditional Chinese medicines including Lead, Cadmium, Chromium, Mercury, Copper and so on3, sometimes people also prefer including arsenic trioxide as toxic heavy metal. Different types of heavy metals in human effect different parts or systems, and the symptoms of poisoning cornerstone be on the nervous, digestive, hematopoietic systems or peo ples metabolism and other body damage. So to accurate detect and limit the content of toxic metals is the key to cling to the people of medication safety, to promote the inter interior(a)ization of traditional Chinese medicines. Recently, themost commonly use detection methods of detection of toxic metals include colorimetric assay and submissive analysis4. With the increasing conductments for toxic metal limits, instrumental analysis method has become the primary means of detection of heavy metals. In this paper, the determination of toxic metals in traditional Chinese medicine samples by atomic emission spectrometry technology are reviewed.1. The national limits for toxic metals in herbal medicines and productIn general, quantitative tests and limit tests accurately determinate the submergences of toxic metals in the form of impurities and contaminants. The latter are unavoidably present in the samples being tested. Member states can elect to use either quantitative tests or l imit tests and their choices will be influenced by the nature of the sample and the contaminants or residues, assessed on a case-by-case basis. Another factor would be that the methods identified, and chosen to be applied to control toxic metals, should be relevant and should meet the requirements at a regional and national level. Some examples of proposed national limits for arsenic and toxic metals in various types of herbal products are shown in Table 15.Table 1. Example of national limits for arsenic and toxic metals in herbal medicines and products2. The sources of toxic metals in traditional Chinese medicine samplesThe toxic metals in traditional Chinese medicines can be from the soil where is contaminated, in the processes of collection and production.3. Atomic emission spectroscopy (AES)Atomic emission spectroscopy (AES) is a method of chemical analysis, when the analyte atoms in solution are aspirated into the excitation region( firing, plasma, arc, or spark at a particula r wavelength) and underwent desolvated, vaporized, atomized, these high-temperature sources provide sufficient nil to promote the atoms into high energy levels, after decaying back to haplesser energy levels by emitting light, the wavelength of the atomic spectral lines gives the identity of the chemical element and the intensity of light proportional to the concentration of atoms, this can be apply to determinate the quantity of elements in a sample. Since all atoms are excited simultaneously, they can be detected simultaneously.3.1 The classification of AESFlame atomic emission spectroscopy(FAES) The energy source is flame, a sample is brought into the flame by a nebulizer in the form of gas, sprayed solution. A flame provides a high-temperature source for desolvating and vaporizing a sample to obtain free atoms for spectroscopic analysis. For atomic emission spectroscopy the flame must also excites the atom to higher excited states. Then subsequently emit light when they retu rning to the ground electronic state. all(prenominal) element emits light at a characteristic wavelength, which is dispersed by a grating or prism(monochromator) and detected by photo detector. Due to its low temperature(17003200C), nitrous oxide-acetylene is the best flame as this gives the highest temperature. FAES used mostly for determination of alkali metals and occasionally calcium, and need internal standard to correct for variations flame6. So FAES is everlastingly used with FAAS together to determinate the content of metals in a sample. Slavica Rai used FAAS/FAES to determinate the elements of Cu, Zn, Mn, Fe, K, Ca, Mg in some of herbal drugs7.Inductively match plasma atomic emission spectroscopy(ICP-AES) Inductively coupled plasma atomic emission spectroscopy(ICP-AES) uses an inductively coupled plasma as thermal source to excite atoms and ions to their excited energy levels and emit electromagnetic radiation at wavelengths characteristic of a particular element8.ICP-AE S has a lot of advantages such as low inter-element interference, multi-element capability, high sensitivity, high concentration range, low chemical interference, with stable and reproducible signal and high degree of selectivity, precision and accuracy(0.33%), can use with gas, liquid or solids samples. Disadvantages are stark spectral interferences(too many emission lines), procedures complicated, consume large Ar gas and operating expense, not possible to determinate the elements of H, N, O, C or Ar in trace levels as they are used in solvents and plasma, and also not possible to determinate F, Cl and noble gases at trace levels as they require high excitation energy.Spark and arc atomic emission spectroscopy For solid samples, spark or arc atomic emission spectroscopy is used for the analysis of metallic elements.4. Determination of toxic metals in traditional Chinese medicine by ICP-AESBecause of its high sensitivity, low detection limit, high precision, wide linear range, mu lti-element analysis, small matrix effects and many other advantages for the detection of most of the metallic elements. ICP-AES has become the most effective method that was widely used in all kinds of traditional Chinese medicines in the determination of toxic metals9. Yan Qing-hua used ICP-AES to determinate 14 kinds of elements Cu, Fe, Zn, Mn, Na, K, Ca, Mg, Cr, Ni, Pb, Se, As, Cd in traditional Chinese medicines for clearing love and detoxification. Showed the determining elements in traditional Chinese medicine by IPC-AES saving time and effort, reducing environmental pollution, good stability, high sensitivity and multi-element simultaneous analysis10. Liu Er-dong used ICP-AES to determinate metallic elements for quality control of Chinese herbal medicines showed this method is accurate and rapid11.4.1 Sampling processWith the development of separation science, sample preparation methods have also been substantially developed, e finickyly the sample preparation method for co mplex material systems, which has gained more attention in recent years. The specific method requires special preparation methods or combination methods according to the specific nature and status of the sample preparation. The traditional Chinese medicines samples are very complicated12, the preparation method normally includes conventional extraction methods such as steam distillation, water extraction, and alcohol precipitation, alcohol precipitation of water, organic solvent extraction, fractionation, absorption. For the determination of toxic metals in traditional Chinese medicine samples, people have made a lot of work in improving the equipment, good analysis methods to improve the experimental measurements. moreover always overlook one more important factor, sampling. So how to improve the accuracy of sampling is also one of the most important topics to be studied.4.2Digestion suss outDigestion is an important process in the determination of toxic metals in traditional Chi nese medicines. The general methods of digestion including ashing, wet digestion, microwave digestion, combustion method and high pull dissolving. But all of these methods have their limitations (1) cant be guaranteed fully adapted to all organic samples (2) the waste of analyte (3) perchloric bitter is flammable and explosible. Li Yang compared the digestion methods of prohibitionist ashing, wet digestion and microwave digestion in the process of determination of elements in periostracum serpentis and periostracum cicadae13. The results showed the microwave digestion with the highest efficiency.The samples of traditional Chinese medicine are always cleaned the sediment and washed with implore water, rewashed with de-ionized water, dried under 80 smashed and filtered through 40 mesh sieve, dried under 80 again for 1h, put into drier for using.4.2.1 Ashing digestionAshing digestion is digest samples at high temperature, this is used to find the total mineral content of a sample. Kuziemska Beata used ashing digestion method to determinate the contents of toxic metallic elements in red clover biomass14.Normal procedure as follows Weighed dry sample 1g (wet 24 g), put it in porcelain crucible, charring with low heat , then ashing in furnaces at 450 for 3 hours, cooled and added a little distilled water, heated slightly to dry, then placed in a high temperature furnace ashing completely, cooled, add 1 1 HNO3 1.0 ml, dissolved with heating, rotary the volume to 25ml.4.2.2 Wet digestionIn the process of wet digestion, normally use the solvent of acid or oxidizing agent to digest the samples. The commonly used acid and oxidizer are as followsNitric acid The most commonly used acid in the process of digestion, it is also a strong oxidant which is widely used to dissolve trace elements in plant samples, get their soluble nitrate. Xue Yan used nitric acid as digestion reagent to detect chromium in medical materials showed the detection limit was 1.42 ng/mL, and the deviations were 1.43%1.79%15.Perchloric acid Can decompose organic component completely, which is used when the other reagents can not digest. However, the heat strong perchloric acid is explosible when contact with organic components, so the operator must be very careful.Aqua regia It is a strong oxidant, can applied to digest inorganic components, such as gold and platinum. Tahar Kebir used aqua regia to digest food plants near a polluted site for the measurement of toxic metals(Fe, Pb, Zn, Ni, Cu, Cd, Mn, Cr and As) and got magnificent results16.Hydrofluoric acid It is an efficient reagent to dissolve silicon-containing material. It can change silicate into SiF4, which is used to digest silicon samples completely. When mixed with nitric acid, could digest TiO2, W, Zr et al.Hydrogen peroxide It is one of the most commonly used oxidants, if combined with HNO3, HCIO4, HCI or mixed acid, the efficiency could be better.Sulfuric acid Strong acid and oxidant.The capacity of these aci d and oxidant are different. In the practical applications, normally use the variety show of two or more inorganic acids with different proportion(HNO3-H2SO4, HNO3-HCIO4, H2SO4-HNO3-HCIO4). It has proven that the optimal digestion reagents are the mixture of HNO3-HCIO4, could digest multiple components simultaneously. Tong Wen-jie used HNO3-HCIO4 to digest sunflower(Helianthus annuus L) and analyzed the mineral elements content17. Cai Yanrong also used HNO3-HCIO4 as digestion reagents in the study of trace elements(Fe, Cu, Zn, Al, K, Na, Ba, Sb, Pb, As) in hair samples18.4.2.3 zap digestionMicrowave digestion requires only a small amount of sample and can digest in short time. It is a widely used digestion method in the determination of elements in herbal drugs. Li Feng-xia used microwave digestion method to test and analyze of inorganic elements in 466 traditional Chinese medicines19 showed that the measurements of each element are within the reference range, and RSD of determina tion is less than 10% for most of detected elements. In Yan Qing-huas study, his experiments also used microwave digestion technology, the recovery of the element reach 96.79%103.47% and RSD less than 5.0%10. Zhang Sheng-bang used HNO3-H2O2 as solvents, microwave digestion to study multi-elements in traditional Chinese medicine Ophiopogon japonicus and Lotus seeds by ICP-AES20.Conclusion and outlookIn recent years, the toxic metals in traditional Chinese medicines are concerned increasing all over the world. The methods of determination of toxic metals are not withal fully unified and also lack of regulation, scientific and systemic research. In the Chinese Pharmacopoeia(2010 version), in addition to the classical colorimetric method, more and more wedded to the using of high sensitivity and precision instruments measurements. ICP-AES has proven to be a quick, high sensitive and multi-elements analysis method. But there are still a lot of problems to be solved, new methods of deter mination of toxic metals are required, we hope there is a even faster and cheaper method to satisfy the measurements of toxic metals for TCMs quick check in the process of import and export. Of course, the determination of toxic metals in Chinese medicine samples is a long-term work, with the development of detection technology, the perceptible levels of toxic metals in traditional Chinese medicines will be increased, thereby enhancing their safety.References1 T. J. Zhang. Chinese Traditional and Herbal Drugs, 2011, 42, 192 P. C. A. Kam S. Liew. Anaesthesia, 2002, 57, 108310893 Catherine Buettner Kenneth J. Mukamal Paula Gardiner Roger B. 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