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1.
Jie Liu Mingxia Wang Lianming Chen Yueting Li Yijun Chen Ziyi Wei Zhixin Jia Wenjuan Xu Hongbin Xiao 《Journal of separation science》2019,42(13):2202-2213
Comprehensive characterization of the large number of compounds existing in traditional Chinese medicines is still a great challenge. In this study, a strategy of precursor ion selected acquisition coupled with target and nontarget data mining was established to systematically characterize the chemical constituents of traditional Chinese medicines. This strategy consisted of four steps: (1) precursor ion selected acquisition was developed to trigger additional tandem mass spectrometry fragmentation reactions, especially for trace constituents; (2) in‐house database of compounds was established and diagnostic characteristics were summarized; (3) compounds were identified by target and nontarget data mining; and (4) compound structures were elucidated based on accurate mass matching and comparison of fragment ions, and isomers were discriminated by the intensity of fragment ions, fragmentation pattern analysis, and calculated log P values. This strategy was successfully applied to comprehensively identify the constituents in Dachuanxiong decoction. Finally, a total of 218 compounds assigned to six categories were characterized, and 107 compounds were characterized by nontarget analysis for the first time. In addition, three new diagnostic characteristics of esters of citric acids were elucidated. This research enriched the material basis of Dachuanxiong decoction and provided a new strategy for identifying the chemical constituents of other traditional Chinese medicines. 相似文献
2.
Changchuan Guo Chong Niu Liming Zhou Wenxin Wang Yanjun Nie Qi Liu Lei Zhang Zhen Chen Weijian Wang Yuwen Xu 《Journal of separation science》2020,43(13):2529-2538
In the present work, a novel database of drug compounds and a rapid screening method based on ultra‐high performance liquid chromatography coupled to high resolution orbitrap mass spectrometry were developed and applied in the screening and identification of targeted and nontargeted antihypertensive adulterants in dietary supplements and herbal medicines. The established screening database includes retention time, exact mass, fragments, isotopic pattern, and MS2 spectra library of the target compounds and thus provides automated search and identification of the targets with a single injection. The nontargeted compounds in the samples are identified through the full MS scan and MS2 data by using the Chemspider database and the data analysis in XCalibur, MassFrontier and TraceFinder software. In addition, this method possesses excellent quantitative capacity. The novel approach was applied to 65 batches of samples that are claimed as “all‐natural” products having the antihypertensive function, among which nine batches were found to be positive. Multiple targeted and nontargeted antihypertensive adulterants were detected at levels ranging from 2.8 to 27.9 mg/g. The novel database and screening method demonstrated herein will be promising and powerful tools for rapid screening of antihypertensive adulterants in dietary supplements and herbal medicines. 相似文献
3.
Rapid discovery of absorbed constituents and metabolites in rat plasma after the oral administration of Zi Shen Wan using high‐throughput UHPLC–MS with a multivariate analysis approach 下载免费PDF全文
Xian‐Na Li Aihua Zhang Hui Sun Yanhua Song Di Zou Xijun Wang 《Journal of separation science》2016,39(24):4700-4711
Zi Shen Wan is a typical formula consisting of three herbs, Phellodendri Amurensis Cortex, Rhizoma Anemarrhenae, and Cortex Cinnamomi, and has been widely used for treating prostatitis and infection diseases. However, it lacks in‐depth research of the constituents of Zi Shen Wan in vivo and in vitro. In this work, ultra high performance liquid chromatography coupled with quadrupole‐time‐of‐flight mass spectrometry and MassLynx software was established to characterize the chemical compositions of Zi Shen Wan in vivo and in vitro. In total, 92 peaks were characterized in vitro and 33 peaks were characterized in vivo based on mass spectrometry and tandem mass spectrometry data. Among the 33 compounds characterized in rat plasma, 22 prototype components absorbed in rat serum and 11 metabolites were identified in vivo. This work was fully reports the chemical constituents of traditional Chinese formula of Zi Shen Wan, it demonstrated that ultra high performance liquid chromatography combined with quadrupole time‐of‐flight mass spectrometry coupled to MassLynx software and multivariate data processing approach could be successfully applied for rapid screening and comprehensive analysis of chemical constituents in vitro and prototype components or metabolites in vivo of traditional Chinese medicine. 相似文献
4.
《Journal of separation science》2018,41(10):2130-2138
Shenxiong glucose injection, a pharmaceutical preparation containing a water extract of the roots of Salvia miltiorrhizae and ligustrazine hydrochloride, is widely used in clinical to treat cardiovascular diseases in China. The chemical components of the water extract have been reported and the cardioprotective effects of the injection have been evaluated. However, the chemical constituents of the injection and their correlations with its pharmacological effects have not been established. In this study, 13 chemical constituents of the injection have been identified or characterized by ultra‐high performance liquid chromatography with diode array detection and electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry. Besides, the potentially active compounds of this preparation that directly act on cardiac cells have been screened by cell extraction and ultra high performance liquid chromatography targeted multiple reaction monitoring. As a result, eight potentially active compounds, danshensu ( 1 ), ligustrazine hydrochloride ( 4 ), salvianolic acid I/H ( 7 ), lithospermic acid ( 8 ), salvianolic acid D ( 9 ), rosmarinic acid ( 10 ), salvianolic acid B ( 12 ), and salvianolic acid C ( 13 ), were obtained and structurally characterized from the 11 target compounds used for screening. The liquid chromatography with quadrupole time‐of‐flight mass spectrometry and liquid chromatography with multiple reaction monitoring tandem mass spectrometry combination method has demonstrated its potency for the screening, detection, and structural identification of bioactive compounds in a complex matrix. 相似文献
5.
《Journal of separation science》2017,40(6):1254-1265
In this study, we propose an integrated strategy for the efficient identification and quantification of herbal constituents using liquid chromatography with mass spectrometry. First, liquid chromatography with quadrupole time‐of‐flight mass spectrometry was employed for the chemical profiling of herbs, where a targeted following nontargeted approach was developed to detect trace constituents by using structural correlations and extracted ion chromatograms. Next, ion pairs and parameters of MS2 of quadrupole time‐of‐flight mass spectrometry were selected to design multiple reaction monitoring transitions for the identified compounds on liquid chromatography with triple quadrupole mass spectrometry. The relative concentration of each constituent was then calculated using a semiquantitative calibration curve. The proposed strategy was applied in a study of chemical interactions between Glycyrrhizae Radix and Coptidis Rhizoma. A total of 140 compounds were identified or tentatively characterized from the herbs, 132 of which were relatively quantified. The visualized quantitative results clearly showed codecoction produced significant constituent concentration variations especially for those with a low polarity. The case study also indicated that the present methodology could provide a reliable, accurate, and labor‐saving solution for chemical studies of herbal medicines. 相似文献
6.
Stefanie Pötz Heinz Wilkes Matthias Witt Brian Horsfield 《Rapid communications in mass spectrometry : RCM》2010,24(8):1185-1197
Four different geological sample types (a crude oil, a crude oil asphaltene, a reservoir core extract and a reservoir core asphaltene) have been characterized by negative ionization electrospray mass spectrometry at low and high mass resolution using a double‐focusing magnetic sector field mass spectrometer. The mass range, shape of the spectra and the signal distribution of the acidic constituents as well as the average molecular weights, the total ion abundance and signal intensity in the spectra were compared for the different sample types. Nominal mass classes have been evaluated and Kendrick mass plots were generated in order to identify homologous series. For the crude oil sample, accurate mass assignments were made by high‐resolution double‐focusing magnetic sector field mass spectrometry (DFMSFMS) and were compared with those obtained by negative ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). With both instrument types, compounds with the molecular composition CnH2n+zO2, among which carboxylic acids predominated, were the main acidic compound class detectable in negative ESI mass spectra. Good agreement was achieved for the double bond class distribution and the carbon number distribution of the O2 class. In addition, minor compound classes could be identified using FTICRMS. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
7.
《Journal of separation science》2017,40(3):663-670
Radix Polygalae, the dried roots of Polygala tenuifolia and P. sibirica , is one of the most well‐known traditional Chinese medicinal plants. It is an important medicinal plant that has been used as a sedative and to improve memory for a number of years in most of Asia. However, the in vivo constituents of the multiple constituents from Radix Polygalae remain unknown. In the current study, ultra high performance liquid chromatography coupled to quadrupole time‐of‐flight mass spectrometry and the MarkerLynxTM software combined with multiple data processing approach were used to study the constituents in vitro and in vivo. A rapid and efficient method for the characterization of multiple constituents in the herbal medicine Radix Polygalae by ultra high performance liquid chromatography coupled to quadrupole time‐of‐flight mass spectrometry is described. In total, 35 compounds in the Radix Polygalae and 13 compounds absorbed into blood were characterized. Of the 35 compounds in vitro, ten were reported for first time. In the 13 compounds in vivo, six were prototype components and seven were metabolites were also elucidated for first time. This work narrowed the range of screening the potentially bioactive components and provided a basis for the quality control and mechanism of action. 相似文献
8.
Identification of chemical constituents in traditional Chinese medicine formula using HPLC coupled with linear ion trap‐Orbitrap MS from high doses of medicinal materials to equivalent doses of formula: Study on Xiang‐Sha‐Liu‐Jun‐Zi‐Jia‐Jian granules 下载免费PDF全文
Zhiwei Lu Qing Wang Meiling Wang Yuehong Liu Shuang Fu Xiaoyan Gao Xudong Tang 《Journal of separation science》2016,39(9):1619-1627
High‐resolution mass spectrometry has been a powerful tool for the research of chemical constituents in traditional Chinese medicine (TCM) formulas. However, the chromatographic peaks were difficult to discriminate clearly in data collection or analysis because of the complexity and the greatly different content of the constituents in TCM formula, which increased the difficulty of identification. In this study, a high‐performance liquid chromatography coupled with linear ion trap‐Orbitrap mass spectrometry based strategy focused on the comprehensive identification of TCM formula constituents was developed. Identification was carried out from a high dose of medicinal materials to equivalent dose of formula. Meanwhile, combined with mass spectrometry data, chromatographic behaviors, reference standards and previous reports, the identification of constituents in Xiang‐Sha‐Liu‐Jun‐Zi‐Jia‐Jian granules was described. 169 compounds were unambiguously or tentatively characterized, mainly including flavonoids, alkaloids, triterpenic acids, triterpene saponins, lactones, sesquiterpenoids and some other compounds. Among them, 11 compounds were unambiguously confirmed by comparing with reference standards. These results demonstrated that the method was effective and reliable for comprehensive identification of constituents of Xiang‐Sha‐Liu‐Jun‐Zi‐Jia‐Jian granules extracts and reveal the material basis of its therapeutic effects. This strategy might propose a research idea for the characterization of multi‐constituents in TCM formula. 相似文献
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Rapid screening,identification, and purification of neuraminidase inhibitors from Lithospermum erythrorhizon Sieb.et Zucc. by ultrafiltration with HPLC–ESI‐TOF‐MS combined with semipreparative HPLC 下载免费PDF全文
Minmin Zhang Hengqiang Zhao Zhiguo Zhao Huijiao Yan Ruimin Lv Li Cui Jinpeng Yuan Daijie Wang Yanling Geng Daicheng Liu Xiao Wang 《Journal of separation science》2016,39(11):2097-2104
We put forward an efficient strategy based on bioassay guidance for the rapid screening, identification, and purification of the neuraminidase inhibitors from traditional Chinese medicines, and apply to the discovery of anti‐influenza components from Lithospermiun erythrorhizon Sieb.et Zucc. Ultrafiltration with high‐performance liquid chromatography and electrospray ionization time‐of‐flight mass spectrometry was employed for the rapid screening and preliminarily identification of anti‐influenza components from Zicao. Semipreparative high‐performance liquid chromatography was used for the rapid separation and purification of the target compounds. NMR spectroscopy, mass spectrometry, and UV spectroscopy were used for further structural identification, and the activity of the compounds was verified by in vitro assay. Five compounds were found to have neuraminidase inhibitory activity by this method. Subsequently, the five compounds were separated by semipreparative high‐performance liquid chromatography with the purity over 98% for all of them by high‐performance liquid chromatography test. Combined with the NMR spectroscopy, mass spectrometry, and UV spectroscopy data, they were identified as alkannin, acetylalkannin, isobutyrylalkannin, β,β‐dimethylacryloylalkannin and isovalerylalkannin. The in vitro assay showed that all five compounds had good neuraminidase inhibitory activities. These results suggested that the method is highly efficient, and it can provide platform and methodology supports for the rapid discovery of anti‐influenza active ingredients from complex Chinese herbal medicines. 相似文献
12.
《Journal of mass spectrometry : JMS》2018,53(4):314-322
The fragmentation pathways of pentacoordinated phenoxyspirophosphoranes were investigated in the positive mode by electrospray ionization multistage mass spectrometry. The results demonstrate that the sodium adducts of the title compounds undergo two competitive fragmentation pathways, and the fragmentation patterns are heavily dependent on the various substituent patterns at the phenolic group. An electron‐withdrawing substituent at the ortho‐position always results in the removal of a corresponding phenol analogue, while cleavage by spiroring opening becomes the predominant fragmentation pathway if an electron‐donating substituent is at the phenolic group. The substituent effects on the competitive fragmentation pathways were further elucidated by theoretical calculations, single crystal structure analysis, and high‐resolution mass spectrometry. The results contribute to the understanding of the gas‐phase fragmentation reactions and the structure identification of spirophosphorane analogues by electrospray ionization multistage mass spectrometry. 相似文献
13.
《Journal of separation science》2017,40(3):646-662
The processing of Juglans mandshurica Maxim. is important to reduce its toxicity and enhance its efficacy. Simple, efficient, and sensitive ultra‐high performance liquid chromatography coupled with a time‐of‐flight mass spectrometry based chemical profiling approach was proposed to rapidly evaluate the chemical difference between fresh and dry samples. Under the optimized ultra‐high performance liquid chromatography and quadrupole time‐of‐flight tandem mass spectrometry conditions, 81 significantly different compounds were rapidly discovered using principal component analysis, and then tentatively identified by comparison with reference substances or inferred through mass spectral fragment ion analysis and literature data. These compounds included 35 naphthoquinones, 11 diarylheptanoids, nine flavonoids, eight triterpenes, 12 phenolic acids, and six aliphatics. The results demonstrated that chemical reactions occurring during processing could be used to elucidate the processing mechanism of Juglans mandshurica Maxim. This study provides a novel approach to identifying complicated components of various complex mixtures in fresh‐raw and dry‐processed traditional Chinese medicines, which could be used as a valid analytical method to further understand the processing mechanisms of these medicines, as well as providing intrinsic quality control of the medicines and their processed products. 相似文献
14.
Qualitative and quantitative analysis of the chemical constituents in Mahuang‐Fuzi‐Xixin decoction based on high performance liquid chromatography combined with time‐of‐flight mass spectrometry and triple quadrupole mass spectrometers 下载免费PDF全文
Yanyan Zhou Xu Wang Haiqiang Jiang Lili Gong Yong Yang Rong Rong 《Biomedical chromatography : BMC》2016,30(11):1820-1834
High‐performance liquid chromatography coupled with time‐of‐flight mass spectrometry (HPLC‐TOF/MS) and high‐performance liquid chromatography–triple quadrupole mass spectrometry (HPLC‐QQQ/MS/MS) were utilized to clarify the chemical constituents of Mahuang‐Fuzi‐Xixin Decoction. There are 52 compounds, including alkaloids, amino acids and organic acids were identified or tentatively characterized by their characteristic high resolution mass data by HPLC‐QQQ/MS/MS. In the subsequent quantitative analysis, 10 constituents, including methyl ephedrine, aconine, songrine, fuziline, neoline, talatisamine, chasmanine, benzoylmesaconine, benzoylaconine and benzoylhypaconine were simultaneously determined by HPLC‐QQQ/MS/MS with multiple reaction monitoring mode. Satisfactory linearity was achieved with wide linear range and fine determination coefficient (r > 0.9992). The relative standard deviations (RSD) of inter‐ and intra‐day precisions were <3%. This method was also validated by repeatability, stability and recovery with RSD <3% respectively. A highly sensitive and efficient method was established for chemical constituents studying, including identification and quantification of Mahuang‐Fuzi‐Xixin decoction. 相似文献
15.
Characterization of the constituents in rat plasma after oral administration of radix polygoni multiflori extracts by ultra‐performance liquid chromatography/quadrupole time‐of‐flight mass spectrometry 下载免费PDF全文
Longfei Lin Hongmei Lin Xingbin Yin Yang Zhao Zhenwen Xia Miao Zhang Xuechun Li Jing Han Changhai Qu Jian Ni 《Biomedical chromatography : BMC》2015,29(10):1541-1547
An ultra‐performance liquid chromatography/quadrupole time‐of‐flight mass spectrometry method was established to detect as many constituents in rat plasma as possible after oral administration of Radix polygoni multiflori (RPM) extract. A C18 column (150 × 2.0 mm, 4 µm) was adopted to separate the samples, and mass spectra were acquired in negative modes. The fingerprints of RPM extract were established, resulting in 39 components being detected. Among these compounds, 29 were identified by comparing the retention times and mass spectral data with those of reference standards and relevant references, and eight compounds were separated and detected in RPM for the first time. In vivo, 23 compounds were observed in dosed rat plasma, 16 of 23 compounds were indicated as prototype components of RPM, and seven compounds were predicted to be metabolites of RPM. A high‐speed and sensitive method was developed and was successfully utilized for screening and characterizing the ingredients and metabolites of RPM. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
16.
Ultra high performance liquid chromatography with synapt high‐definition mass spectrometry and a pattern recognition approach to characterize chemical constituents and rat metabolites after the oral administration of Phellinus igniarius 下载免费PDF全文
Yu Dong Huiyu Wang Yang Zhang Na An Yue Zhang Dan Shou 《Journal of separation science》2015,38(7):1137-1148
Phellinus igniarius has antibacterial, antiviral, antioxidative, antitumor, and antimutagenic effects. In this study, an integrative pattern recognition approach using principal component analysis and orthogonal partial least squares discriminant analysis was successfully applied for the rapid analysis of natural compounds in traditional Chinese medicine. An ultra high performance liquid chromatography with synapt high‐definition mass spectrometry method and MassLynx software was used. This method employed gradient elution to rapidly analyze and characterize chemical constituents and metabolites after the oral administration of a P. igniarius ethanol extract. There were 24 peaks within 10 min of the analysis time and 20 of these were identified or tentatively characterized on the basis of their fragmentation behaviors. In the S‐plot of the orthogonal partial least squares discriminant analysis, 27 ions were extracted to make the serum. Among them, nine absorbed the prototype components and 18 metabolites were identified in vivo. Glucuronidation, oxidation, and methylation were the major metabolic reactions. This study is the first systematic analysis and characterization of the chemical constituents and metabolites in an ethanol extract of P. igniarius. This method can be applied to the rapid analysis and characterization of constituents in rat serum after the oral administration of other compounds used in traditional Chinese medicines. 相似文献
17.
Zhang‐xiao Peng Yan Wang Xue Gu Yuan‐yuan Wen Chao Yan 《Biomedical chromatography : BMC》2013,27(12):1759-1766
Several Chinese herbs, namely, Pu‐Gong‐Ying, Gan‐Cao, Chai‐Hu, Mu‐Xiang, Gua‐Lou and Huang‐Yao‐Zi, are frequently used in complex traditional Chinese medicing formulas for breast hyperplasia and breast tumor therapy. The pharmacological effects of these Chinese herbs are all described as ‘clearing heat‐toxin and resolving masses’ in traditional use. However, the chemical profiles of anti‐breast cancer constituents in these herbs has not been investigated so far. In this study, a bioactivity‐oriented screening platform, which was based on a human breast cancer MCF‐7 cellular model, semi‐preparative high performance liquid chromatography coupled with ultraviolet spectrophotometry and ultraperformance liquid chromatography coupled to quadrupole‐time‐of‐flight mass spectrometer, was developed to rapidly screen the six Chinese herbs. Two potential anti‐breast cancer compounds, which were costunolide (Cos) and dehydrocostus lactone (Dehy), were identified in Mu‐Xiang. Combination of the two compounds showed a synergism on inhibiting the proliferation of MCF‐7 cells in vitro, which exhibits a potential application prospect for breast cancer therapy. This bioactivity‐oriented screening strategy is rapid, economical, reliable and specific for screening potential anti‐breast cancer compounds in traditional Chinese medicines. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
18.
Yumei Wang Qi Liu Songjie Fan Xueting Yang Linlin Ming Huimin Wang Jianhua Liu 《Journal of separation science》2019,42(19):3054-3066
Corn silk is a well‐known traditional Chinese medicine that has been widely used for its antidiabetic, antioxidant, antihyperlipidemic, and other effects in China for thousands of years. Numerous studies have revealed that corn silk contains multiple bioactive constituents that are beneficial for human health. However, the constituents of corn silk in vivo remain ambiguous. In this study, high‐throughput ultra‐high‐performance liquid chromatography combined with quadrupole time‐of‐flight mass spectrometry technology using multivariate statistical analysis was established to systematically investigate the constituents migrating into blood from corn silk aqueous extract. As a result, 76 compounds were identified, including caffeic acid and ten of its derivatives, (E)‐p‐coumaric acid and two of its derivatives, ferulic acid and four of its derivatives, and five flavones. Among the identified constituents, 21 constituents, including nine prototype components and 12 metabolites derived from eight components, were characterized in sequence. Based on the significance of the results, the applied approach was powerful for the accurate determination and rapid screening of bioactive components from corn silk aqueous extract. The obtained results are valuable for the in‐depth understanding and further pharmacological study of corn silk aqueous extract. 相似文献
19.
Hang Lin Changfa Zhang Yuanjing Lin Yiqun Chang Jacques Crommen Qiqin Wang Zhengjin Jiang Jialiang Guo 《Journal of separation science》2019,42(11):1980-1989
A novel strategy was successfully developed for screening trypsin inhibitors in traditional Chinese medicines based on monolithic capillary immobilized enzyme reactors combined with liquid chromatography‐tandem mass spectrometry. Organic polymer based monolithic enzyme reactors were firstly prepared by covalently bonding trypsin to a poly(glycidyl methacrylate‐co‐poly (ethylene glycol) diacrylate) monolith by the ring‐opening reaction of epoxy groups. The activity and kinetic parameters of the obtained monolithic trypsin reactors were systematically evaluated using micro‐liquid chromatography. Fourier transform infrared spectroscopy and scanning electron microscopy were also used to characterize the monolithic trypsin reactors. The resulting functional and denatured monolithic trypsin reactors were applied as affinity solid‐phase extraction columns, and offline coupled with a liquid chromatography‐tandem mass spectrometry system to construct a binding affinity screening platform. Subsequently, the proposed platform was applied for screening trypsin binders in a Scutellaria baicalensis Georgi extract. Three compounds, namely scutellarin, baicalin, and wogonoside were identified, and their inhibitory activities were further confirmed via an in vitro enzymatic inhibition assay. Additionally, molecular docking was also performed to study the interactions between trypsin and these three compounds. 相似文献
20.
Audrey Hecka Benoît Maunit Frédéric Aubriet Jean‐François Muller 《Rapid communications in mass spectrometry : RCM》2009,23(6):885-898
Five well‐known active naphtodianthrone constituents of Hypericum perforatum (St John's Wort) extracts have been investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FTICRMS) and ESI‐FTICRMSn. The studied compounds were hypericin, pseudohypericin, protohypericin, protopseudohypericin (biosynthetic precursors of the two former compounds, respectively) and isopseudohypericin (alkaline degradation product of pseudohypericin). Dissociation mass spectrometry measurements performed on the [M–H]? ion presented a variable efficiency as a function of the used activation mode. Sustained off‐resonance irradiation collision‐induced dissociation (SORI–CID) only led to a restricted number of fragment ions. In contrast, IRMPD ensured the detection of numerous product ions. Ions detected in ESI‐FTICRMS and ESI‐FTICRMSn experiments were measured with a very high mass accuracy (typically mass error is lower than 0.5 mDa at m/z close to 500) that allowed unambiguous formulae to be assigned to each signal observed in a mass spectrum. In spite of similar structures, specific fragmentation patterns were observed for the different compounds investigated. This study may be useful in the future to characterize in natural extracts these compounds (or derivatives of these compounds) by liquid chromatography/tandem mass spectrometry (LC/MS/MS) experiments by considering the MS/MS transitions highlighted in this paper. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献