The Development of Time-of-flight Mass Spectrometry( TOF-MS) and Its Applications in Screening Food Hazard Factors

The time-of-flight mass spectrometry(TOF-MS),one of the mass spectrometry techniques,has been widely applied in the field of rapid screening of food hazard factors as a superior analysis technique because of its wide mass range,high resolution and mass measurement accuracy,high sensitivity and high analysis speed.In this paper,research progresses of TOF-MS on the detection of food additives,food contaminants and residues,illegal additives,pesticide residues,veterinary drug residues and mycotoxin were reviewed,and its probable approaching applications were prospected.

Offline two-dimensional liquid chromatography coupled with ion mobility-quadrupole time-of-flight mass spectrometry enabling fourdimensional separation and characterization of the multicomponents from white ginseng and red ginseng

Inherent complexity of plant metabolites necessitates the use of multi-dimensional information to accomplish comprehensive profiling and confirmative identification.A dimension-enhanced strategy,by offline two-dimensional liquid chromatography/ion mobility-quadrupole time-of-flight mass spectrometry(2 D-LC/IM-QTOF-MS)enabling four-dimensional separations(2 D-LC,IM,and MS),is proposed.In combination with in-house database-driven automated peak annotation,this strategy was utilized to characterize ginsenosides simultaneously from white ginseng(WG)and red ginseng(RG).An offline 2 DLC system configuring an Xbridge Amide column and an HSS T3 column showed orthogonality 0.76 in the resolution of ginsenosides.Ginsenoside analysis was performed by data-independent high-definition MSE(HDMSE)in the negative ESI mode on a Vion?IMS-QTOF hybrid high-resolution mass spectrometer,which could better resolve ginsenosides than MSEand directly give the CCS information.An in-house ginsenoside database recording 504 known ginsenosides and 58 reference compounds,was established to assist the identification of ginsenosides.Streamlined workflows,by applying UNIFI?to automatedly annotate the HDMSEdata,were proposed.We could separate and characterize 323 ginsenosides(including 286 from WG and 306 from RG),and 125 thereof may have not been isolated from the Panax genus.The established 2 D-LC/IM-QTOF-HDMSEapproach could also act as a magnifier to probe differentiated components between WG and RG.Compared with conventional approaches,this dimensionenhanced strategy could better resolve coeluting herbal components and more efficiently,more reliably identify the multicomponents,which,we believe,offers more possibilities for the systematic exposure and confirmative identification of plant metabolites.

Dimension-Enhanced Ultra-High Performance Liquid Chromatography/Ion Mobility-Quadrupole Time-of-Flight Mass Spectrometry Combined with Intelligent Peak Annotation for the Rapid Characterization of the Multiple Components from Seeds of Descurainia sophia

The complex composition of herbal metabolites necessitates the development of powerful analytical techniques aimed to identify the bioactive components.The seeds of Descurainia sophia(SDS)are utilized in China as a cough and asthma relieving agent.Herein,a dimension-enhanced integral approach,by combining ultra-high performance liquid chromatography/ion mobility-quadrupole time-of-flight mass spectrometry(UHPLC/IMQTOF-MS)and intelligent peak annotation,was developed to rapidly characterize the multicomponents from SDS.Good chromatographic separation was achieved within 38 min on a UPLC CSH C18(2.1×100 mm,1.7μm)column which was eluted by 0.1%formic acid in water(water phase)and acetonitrile(organic phase).Collision-induced dissociation-MS^(2)data were acquired by the data-independent high-definition MS^(E)(HDMS^(E))in both the negative and positive electrospray ionization modes.A major components knockout strategy was applied to improve the characterization of those minor ingredients by enhancing the injection volume.Moreover,a self-built chemistry library was established,which could be matched by the UNIFI software enabling automatic peak annotation of the obtained HDMS^(E)data.As a result of applying the intelligent peak annotation workflows and further confirmation process,a total of 53 compounds were identified or tentatively characterized from the SDS,including 29 flavonoids,one uridine derivative,four glucosides,one lignin,one phenolic compound,and 17 others.Notably,four-dimensional information related to the structure(e.g.,retention time,collision cross section,MS^(1)and MS^(2)data)was obtained for each component by the developed integral approach,and the results would greatly benefit the quality control of SDS.

Identification of serum biomarkers for diagnosing stage Ⅰ lung adenocarcinoma by MALDI-TOF mass spectrometry

Objective To identify specific biomarkers that could improve early diagnosis of lung adenocarcinoma using matrix-assisted laser desorption/ionization (MALDI) technology. Methods Serum samples were isolated from 17 patients with stage Ⅰ lung adenocarcinoma and 17 age-and sex-matched healthy controls,and the serum proteomic profiles were obtained by matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry. Results Compared with healthy control group,two highly expressed potential biomarkers were identified with the relative molecular weights of 6 631.64 Da and 4 964.21 Da. The two best novel protein peaks were automatically chosen for the system training and the development of the constructed model. The constructed model was then used to test an independent set of masked serum samples from 15 lung adenocarcinoma patients and 22 healthy individuals. The analysis yielded a sensitivity of 93.3%,and a specificity of 95.5%. Conclusion These results suggest that MALDI-TOF-MS ProteinChip technology is a quick,convenient,and high-output analyzing method that is capable of selecting several relatively potential biomarkers from the serum of lung adenocarcinoma patients and may have a clinical value in the future,and will provide clues to identifying new serologic biomarkers of lung adenocarcinoma.

Characterization of Carbon Plasma Evolution Using Laser Ablation TOF Mass Spectrometry

In this work, a time-of-flight （TOF） mass spectrometer has been used to investigate the distribution of intermediate species and formation process of carbon clusters. The graphite sample was ablated by Nd：YAG laser （532 nm and 1064 nm）. The results indicate that the maximum size distribution shifted towards small cluster ions as the laser fluence increased, which happened because of the fragmentation of larger clusters in the hot plume. The temporal evolution of ions was measured by varying the delay time of the ion extraction pulse with respect to the laser irradiation, which was used to provide distribution information of the species in the ablated plasma plume. When the laser fluence decreased, the yield of all of the clusters obviously dropped.

Characterization of 4-Aryl-5-ethoxycarbonyl-6-methyl-3,4-dihydro-pyrimidin-2(1H)-thiones by EI-TOF Mass Spectrometry

The electron impact （EI） time-of-flight mass spectra （TOFMS） of the title compounds （ thioxo-Biginelli compounds） were studied to establish their fragmentation pathways. With a TOF instrument of high resolution, the exact mass for each fragment was determined. These data were used to infer the molecular formulas and the ionic elemental compositions for all the compounds through interpretation by software. By further applying chemical intuition, majority of the fragmentation ions were fully assigned. All the compounds give strong signals（ average 76% ） for their molecular ions in the El spectra. Two kinds of characteristic fragmentation pathways from the molecular ion were observed. One is related to the loss of the ester group, forming a resonance stabilized ion with a moderate abundance（ average 40% ）. The other concerns the loss of the aromatic-ring radical, forming another resonance stabilized ion at m/z 199 with a high abundance（ average 79% ）, from which further important fragmentations including the formation of an ion at m/z 171 （average 24% ） by the loss of C2H2 （via the McLafferty rearrangement）, and an ion at m/z 153（ average 10% ） by the elimination of a water molecule preceed. In addition, ion [ M - Et ]^＋ with a high abundance（average 62% ） is a characteristic for the Biginelli compounds with an ethoxycarbonyl group. Differences and similarities among the fragmentations observed from the EI-TOFMS of oxo-Biginelli compounds are discussed.

Studies on Fragmentation Regularity of 5-Methoxycarbonyl- 4-substituted-6-methyl-3,4-dihydropyrimidin-2(1H)-ones by Time-of-flight Mass Spectrometry

The electron impact time-of-flight(TOF) mass spectra of the title compounds were studied to establish their fragmentation processes. With the high resolution of the TOF instrument, the exact mass for each fragment was determined. These data were used to infer the molecular formulas and the elemental compositions for all the molecular ions and fragments through software interpretation. By further applying the fragmentation regularity, the majority of ions were fully assigned. The main fragmentation pathways of the title compounds include the formation of molecular ions by the loss of R 1 groups in the 4-position and the ester groups in the 5-position. The formed ion can be further fragmented by the elimination of MeOH.

MicrobMatcher: a microbial comparison software based on matrix-assisted laser desorption/ionization with time-of-flight mass spectrometry

Matrix-assisted Laser Desorption/Ionization with Time-of-flight Mass Spectrometry (MALDI-TOFMS) was investigated as a method for the rapid identifica-tion of species. Current demand in microbial identi-fication is how to compare unknown strains to the known one quickly, semi-automatically and accurately. In this paper, we present a software tool that allows flexibly microbial matching in a user-friendly way, by letting the users to customize comparison parameters including: in vitro transcription enzyme, mass tolerance,minimum fragment length, intensity threshold and corresponding weights. We provide three spectral scoring functions to compute the affin-ity between the species. Therefore, the precision of microbial comparison increases. To test and verify this tool, we employed experimental spectral data based on MALDI-TOFMS and the gene sequences of E.coli and Salmonella. This software is written in Java for cross-platform intention.

Application of Liquid Chromatography-High Resolution Time-of-flight Mass Spectrometry in the Detection of Raw Milk and Dairy Products

Milk and dairy products are more and more popular with consumers due to their various nutrients, and their quality and safety issues have always been concerned. Therefore, the development of rapid, accurate and simple screening techniques is of great significance. Liquid chromatography-high resolution time-of-flight mass spectrometry has high-resolution and high-throughput detection functions, and has gradually begun to be applied in the detection of milk and dairy products. This paper summarized the application of milk and dairy products in liquid chromatography-high resolution time-of-flight mass spectrometry, laying a foundation for the development of new methods.

Lysophosphatidylcholine Biomarkers of Lung Cancer Detected by Ultra-performance Liquid Chromatography Coupled with Quadrupole Time-of-flight Mass Spectrometry

Centrifugal ultrafiltration after methanol extraction of whole plasma was used as an optimal condition for the preparation of blood plasma before metabonomic studies. The plasma samples from 102 lung cancer patients and 34 healthy volunteers were prepared with this approach. With ultra-performance liquid chromatography（UPLC） coupled with quadrupole time-of-flight mass spectrometry（Q-TOF MS） analysis, the samples were investigated in order to find potential disease biomarkers. After data acquisition, orthogonal signal correction partial least squares models were built to differentiate the healthy volunteers from lung cancer patients and to identify metabolites that showed significantly different expression between the two groups. Several metabolite ions were identified as potential biomarkers according to the variable importance in the project（VIP） value in both ion modes. Five lysophosphatidylcholines were further identified as specifically lysoPC 16：0, isomer of lysoPC 16：0, lysoPC 18：0, lysoPC 18：1 and lysoPC 18：2. These results suggest that UPLC coupled with Q-TOF MS is an effective technique for the analysis of plasma metabolites in metabonomic studies.

Screening and Identifying of Nephrotoxic Compounds in Lithospermum erythrorhizon Using Live-cell Fluorescence Imaging and Liquid Chromatography Coupled with Tandem Mass Spectrometry

In order to identify the potential nephrotoxic compounds in traditional Chinese medicine Lithospermum erythrorhizon,it was separated into serial fractions according to their polarities.An in vitro method was utilized to determine the nephrotoxicity of these fractions with the help of fluorescence image analysis.As a result,the primary fraction A05 and its secondary fractions C06 ＂C09 and C12 ＂C14 were found to have significant toxicity to LLC-PK1 cell line,as determined by the survive rate less than 20% after they were treated with these fractions.These potential nephrotoxic fractions were further analyzed by multistage and high resolution mass spectrometry.The main compounds in these fractions were tentatively identified to be acetylshikonin,isobutyrylshikonin,β,β＇-dimethyla-cryloylshikonin,and isovalerylshikonin,which may bring nephrotoxicity.

Improved preparation and identification of aristolochic acid-DNA adducts by solid-phase extraction with liquid chromatography-tandem mass spectrometry

Aristolochic acid （AA） is a known nephrotoxin and potential carcinogen, which can form covalent DNA adducts after metabolic activation in vivo and in vitro. A simple method for preparation and characterization of aristolochic acid-DNA adducts was developed. Four AA-adducts were synthesized by a direct reaction of AAI/AAII with 2′-deoxynucleosides. The reaction mixture was first cleaned-up and pre-concentrated using solid phase extraction （SPE）, and further purified by a reversed-phase high performance liquid chromatography （HPLC）. By the application of developed SPE procedure, matrices and byproducts in reaction mixture could be greatly reduced and adducts of high purity （more than 94% as indicated by HPLC） were obtained. The purified AA-DNA adducts were identified and characterized with liquid-electrospray ionization-quadrupole-time of flight-mass spectrometry （LC-ESI-Q-TOF-MS/MS） and LC-Diode array detector-fluorescence （LC-DAD-FL） analysis. This work provides a robust tool for possible large-scale preparation of AA-DNA adduct standards, which can promote the further studies on carcinogenic and mutagenic mechanism of aristolochic acids.

基于UPLC-Q-TOF-MS/MS的“略麻1号”茎秆与块茎化学成分分析

目的:对“略麻1号”茎秆与块茎化学成分进行比较研究。方法:采用超高效液相色谱-四极杆飞行时间质谱法(UPLC-Q-TOF-MS/MS),Xbridge BEH C_(18)色谱柱(100 mm×2.1 mm,1.7μm),以0.1%甲酸水溶液-乙腈为流动相进行梯度洗脱,流速为0.3 mL·min^(–1);扫描方式采用正、负离子Full-ddMS2模式下采集数据;结合对照品、相关文献及质谱裂解规律对样品中成分的二级质谱数据进行分析。结果:从“略麻1号”茎秆中共鉴定出153个化合物,包括酚类20个、有机酸类46个、黄酮类11个、氨基酸类12个、生物碱类14个、其他类50个;从“略麻1号”块茎中共鉴定出126个化合物,包括酚类21个、有机酸类36个、氨基酸类13个、生物碱类11个、其他类45个。结论:“略麻1号”茎秆和块茎在物质基础上差异较大,在开发应用中应予以区别,茎秆具有较高的开发应用价值。

MALDI-TOF MS法快速鉴定散装即食食品中3种食源性致病菌

本研究旨在利用基质辅助激光解吸电离飞行时间质谱法(Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry,MALDI-TOF MS)快速检测并鉴定散装即食食品中的沙门氏菌、金黄色葡萄球菌和蜡样芽孢杆菌3种食源性致病菌。通过对点样方式、前处理方式、不同培养基及培养时间等各项实验条件的优化筛选确定最佳方法,并考察其检测限和稳定性,同时用所建立的方法与多重PCR法、VITEK 2等生化鉴定法进行结果比对,比较三者鉴定结果的一致性,最后进行批量食品样本检测来探寻MALDI-TOF MS鉴定法在散装即食食品中的适用性。结果表明,三种目标菌同一批次及不同传代次数的鉴定得分均大于95%,变异系数均小于2%,所建立的方法重复性和稳定性良好,且检测限为10^(5)CFU/mL,MALDI-TOF MS菌株鉴定结果与多重PCR法、生化鉴定法结果高度一致,且比二者检测用时更短,更加特异高效;在点样方式上,相较于夹心法与混合干滴法,三种覆盖法点样平均鉴定得分更高,均为99.9%,其中1μL+1μL覆盖法点样可获得的平均峰数目更多,特征峰更复杂且强度更高;而在前处理方式上,甲酸乙腈法与其他两种菌体处理方法相比可获得更多的出峰量和更高的峰强度,平均鉴定得分均在98%以上,且与数据库中图谱匹配度更高。综上所述,MALDI-TOF MS法在致病菌鉴定方面不仅灵敏特异、准确快速,且操作简便、结果直观,作为国标法的有力补充,为食源性致病菌的分析鉴定与分型溯源提供了新思路。

Time-of-Flight Mass Spectrometer with Transaxial Ion Reflector

Two variants of application of a transaxial mirror with stigmatic spatial time-of-flight focusing in the time-of-flight mass spectrometer have been considered. In the first variant, the transaxial mirror is used as an ion reflector in the ordinary scheme of the time-of-flight mass reflectron. In the second variant, the transaxial mirror simultaneously fulfills the function of the ion reflector and corrector of aberrations caused by the energy spread of ions in the package, formed by the ion source of the mass reflectron. The expressions defining the conditions of stigmatic spatial time-of-flight focusing in the transaxial mirror and the combined system consisting of an ion source and a mirror have been derived. The relationships between geometrical and electrical parameters of three- and four-electrode transaxial mirrors realizing these conditions have been obtained by numerical calculations.

基于UPLC-Q-TOF MS鉴定复方香薷水化学成分

采用超高效液相色谱-四极杆串联飞行时间质谱(UPLC-Q-TOF MS)技术对中药复方香薷水的化学成分进行快速分析鉴定。通过色谱峰响应程度和分离效果优化复方香薷水的前处理方法和仪器条件;采用Agi⁃lent Phe Hex(150 mm×2.1 mm,1.9µm)色谱柱进行分离,以0.1%甲酸水溶液-乙腈为流动相进行梯度洗脱,柱温35℃,流速0.3 mL/min;通过正、负两种离子模式采集复方香薷水的质谱数据,得到精确质量数和二级碎片,结合对照品、Pubchem、安捷伦中药化合物质谱数据库和文献报道等信息对其化合物进行分析鉴定。鉴定出复方香薷水的112个成分,其中黄酮类22个,苯丙素类20个、有机酸18个、萜类14个、生物碱11个、氨基酸5个以及其他类型化合物22个。该研究全面阐述了复方香薷水的化学物质基础,为其质量控制和药效物质研究提供了理论依据。

基于UPLC-Q-TOF-MS和多元统计分析樟帮米泔水漂白术漂制过程中化学成分的动态变化研究

目的研究樟帮米泔水漂白术漂制过程中化学成分的动态变化,为白术漂制工艺的合理制定及炮制机制的阐释提供参考。方法以白术生品及其5个不同漂制阶段的漂制品(第1、2阶段漂制品分别为生品用9倍量米泔水各漂12、24 h;第3-5阶段漂制品分别为生品先用9倍量米泔水漂24 h,再用9倍量清水各漂12、24、48 h,漂洗温度均为26℃)为研究对象,采用超高效液相色谱串联四极杆飞行时间质谱法(UPLC-Q-TOF-MS)检测其化学成分,以0.1%甲酸水溶液(A)-乙腈(B)为流动相进行梯度洗脱(0-5 min,5%-30%B;5-14 min,30%-60%B;14-23 min,60%-70%B;23-31 min,70%-95%B;31-32 min,95%-5%B;32-35 min,5%B),柱温40℃,进样量2μL,流速0.3 mL·min^(-1);运用电喷雾离子源(ESI),在正离子模式下进行扫描并采集质谱数据,扫描范围m/z 50-1250;利用PeakView 1.2进行数据分析,结合对照品、chemicalbook数据库及相关文献对白术生品及其5个不同漂制阶段漂制品的化学成分进行鉴定;质谱数据通过MarkerView1.2软件归一化处理后应用多元统计分析方法找出差异化合物,分析差异化合物的相对含量随漂制时间不同的变化规律。结果从白术生品及其5个不同漂制阶段漂制品中共鉴别出55个化学成分,包含白术内酯Ⅰ、Ⅱ、Ⅲ等在内的40个共有成分。其中,从白术生品、第1-5阶段漂制品中分别鉴别出了53、47、49、49、44、46个成分。与白术生品比较,漂制过程中新增了vitexin和dihydrosyrindine 2个成分,未检测到聚-L-组氨酸、尿苷等9个成分,而9-hydroxy-7-oxo-7H-furo[3,2-g]chromen-4-ylβ-D-glucopyranoside、4-octylbenzoic acid等4个成分在漂制过程中呈消失-出现的变化趋势。多元统计分析筛选出18个差异化合物,其中白术内酯Ⅰ、Ⅱ、Ⅲ这3个差异化合物的相对含量随着漂制时间的延长均呈现先上升后下降的变化趋势,且都是生品中为最低,第3阶段漂制品中为最高。结论漂制辅料(清水和米泔水)和漂制时间是白术漂制过程中化学成分产生动态变化的主要原因。漂白术饮片若以白术内酯Ⅰ、Ⅱ、Ⅲ为指标性成分和药效成分,则白术合理的漂制工艺为:白术生品先用9倍量米泔水漂24 h,再用9倍量清水漂12 h。该实验可为樟帮特色米泔水漂白术炮制科学内涵的阐释提供科学依据。

基于UPLC-Q-TOF/MS技术的成人草酸钙尿石症血液代谢组学研究

目的基于超高效液相色谱-四极杆飞行时间质谱(UPLC-Q-TOF/MS)技术,通过血液代谢组学寻找成人草酸钙尿石症潜在的生物标志物和代谢机制,以指导草酸钙结石的临床诊治。方法前瞻性收集2017年10月—2018年7月北京友谊医院收治的36例双侧上尿路草酸钙结石患者的血液样本并与36例健康体检者的血液样本对照。采用UPLC-Q-TOF/MS技术进行代谢指纹图谱分析。采用主成分分析(PCA)和正交偏最小二乘判别分析(OPLS-DA)对多元数据进行分析。通过对比人类代谢组数据库确定潜在的生物学标记物。最后对所鉴定的化合物行代谢通路分析并构建代谢网络图。结果PCA和OPLS-DA结果显示健康对照者与结石患者血液代谢物存在显著差异。进一步鉴定出包括亚油酸、枸橼酸、尿酸等29种与草酸钙结石患者血液相关的代谢物,以及胆汁酸合成通路、脂肪酸生物合成通路、甘油磷脂代谢通路、鞘脂代谢通路和嘌呤代谢通路等9条血液代谢通路。结论基于UPLC-Q-TOF/MS平台进行血液代谢组学分析,找到了29种成人草酸钙尿石症的潜在血液生物标志物,而嘌呤代谢与脂质代谢可能与草酸钙结石的成因相关。

基于便携GC-MS和HS/SPME-GC×GC-TOF MS分析化州橘红与广西橘红成分差异

为探究不同产地橘红挥发性成分之间的差异,本研究采用便携气相色谱-质谱(GC-MS)和顶空固相微萃取结合全二维气相色谱-飞行时间质谱(GC×GC-TOF MS)技术分析化州橘红和广西橘红的挥发性成分。结果表明,便携GC-MS只能初步区分化州橘红和广西橘红,不能确定化州橘红的特征标志物;利用主成分分析法(PCA)和正交偏最小二乘法(OPLS-DA)对GC×GC-TOF MS实验数据进行处理,根据|p(corr)|>9和|p|>0.06结合VIP>1.1,共筛选出10种化州橘红标志物。该研究为化州橘红药材的质量评价与鉴定提供了依据,也为其他中药质量评价提供了方法参考。