1，3-二甲基尿嘧啶二聚体的飞行时间质谱裂解规律研究

采用不同进样方式、不同电子轰击能量和不同反应气压力测定了1,3 二甲基尿嘧啶二聚体(DMUD) 的4个立体异构体A、B、C、D的化学电离(CI)和电子轰击电离(EI)飞行时间质谱.不同方式所测得的CI谱结 果一致,4个异构体出现了强度不同的准分子离子峰(m/z=281),由此推断它们结构之间的相对稳定性次序为: B(trans syn)>D(cis syn)>A(trans anti)>C(cis anti).这一结论被低能量(25eV)电子轰击的EI谱所证实, 并且与合成产物的比例相吻合.EI谱用任何方式测谱均不出现分子离子峰(m/z=280),而出现其单体离子(m/z =140)且为基峰。给出了DMUD的飞行时间质谱裂解途径,同时对CI谱的裂解碎片进行了细致的讨论.     

Evidence of simple intramolecular rearrangement at polymer end groups in secondary ion mass spectrometry

Polystyrenes with various end groups were analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS). These end groups were obtained by termination of the active anionic group by sulfonate or chlorosilane derivatives. Characteristic end group fragments for each sulfonate derivative were observed. On the one hand, for PS capped by methyl sulfonate, or -(CH(2))(4)-O-SO(2)-CH(3), almost complete end group fragment is observed at m/z 95 and a [O-SO(2)-CH(3)](-) molecular structure. On the other hand, when PS is terminated by silyl methyl sulfonate, or -Si(CH(3))(2)-(CH(2))(3)-O-SO(2)-CH(3), the most characteristic fragment in the fingerprint secondary ion mass spectrum is located at m/z 153 with [Si(CH(3))(2)-O-SO(2)-CH(3)](+) and the complete end group peak, [Si(CH(3))(2)-(CH(2))(3)-O-SO(2)-CH(3)](+), at m/z 201, is absent. According to the molecular structure, characteristic end group secondary ions can be emitted as complete or rearranged fragments. Various silylalkyl alcohol or sulfonate functionalities are analyzed and fragmentation pathways are discussed. To our knowledge, this is the first time that such rearrangement at silyl functions has been observed and demonstrated in fingerprint secondary ion mass spectra. Copyright 1999 John Wiley & Sons, Ltd.     

Identification of isomeric 5-hydroxytryptophan- and oxindolylalanine-containing peptides by mass spectrometry

Cells continuously produce reactive oxidative species that can modify all cellular components. In proteins, for example, cysteine, methionine, tryptophan (Trp), and tyrosine residues are particularly prone to oxidation. Here, we report two new approaches to distinguish two isomeric oxidation products of Trp residues, i.e. 5-hydroxytryptophan (5-HTP) and oxindolylalanine (Oia) residues, in peptides. First, 2-nitrobenzenesulfenyl chloride, known to derivatize Trp residues in position 2 of the indole ring, was used to label 5-HTP residues. The mass shift of 152.98 m/z units allowed identifying 5-HTP- besides Trp-containing peptides by mass spectrometry, whereas Oia residues were not labeled. Second, fragmentation of the Oia- and 5-HTP-derived immonium ions at m/z 175.08 produced ions characteristic for each residue that allowed their identification even in the presence of y(1) ions at m/z 175.12 derived from peptides with C-terminal arginine residues. The pseudo MS(3) spectra acquired on a quadrupole time-of-flight hybrid mass spectrometer displayed two signals at m/z 130.05 and m/z 132.05 characteristic for Oia-containing peptides and a group of six signals (m/z 103.04, 120.04, 130.04, 133.03, 146.04, and 148.04) for 5-HTP-cointaining peptides. In both cases, the relative signal intensities appeared to be independent of the sequence providing a specific fingerprint of each oxidative modification.     

Electrosprayed droplet impact/secondary ion mass spectrometry

A new ionization method, electrosprayed droplet impact ionization (EDI), has been developed for mass spectrometry. The charged droplets formed by electrospraying 1 M acetic acid aqueous solution are sampled through an orifice with a diameter of 400 μm into the first vacuum chamber, transported into a quadrupole ion guide and accelerated by 10 kV after exiting the ion guide. The m/z of the primary droplet projectiles range from 10 000 to 50 000. The droplets impact on a dry solid sample deposited on a stainless steel substrate. No matrix was used for the sample preparation. The secondary ions formed by the impact are transported to a second quadrupole ion guide and mass-analyzed by an orthogonal TOF-MS. Intense molecular-related ions are detected for drugs, amino acids, peptides and proteins. EDI is found to be very sensitive to molecules present near the surface of the sample.     

Determination of levamisole in feeds by liquid chromatography coupled to electrospray mass spectrometry on an ion trap

Test methods have to be developed by laboratories for official control to monitor possible misuse of veterinary drugs in animal productions, also through feeding stuff. A novel method for identification and quantification of levamisole in feeds by liquid chromatography coupled to electrospray mass spectrometry in an ion trap (LC/ESI-MS/MS) is herein described; after a single-step cleanup by liquid-liquid extraction from the feed and separation by reversed-phase liquid chromatography, levamisole was determined and unambiguously confirmed by tandem mass spectrometry, on the basis of two product ions. The method was in-house validated, according to the Regulation 882/2004/EC, evaluating trueness, repeatability, within-laboratory reproducibility, ruggedness, specificity, and the limit of quantification (LOQ). The method is reliable and specific for complete and complementary feeds for pigs, cattle, rabbits and poultry; very good mean recoveries (higher than 92 %) and precision (RSD values?相似文献   

Characteristic ion clusters as determinants for the identification of pyrrolizidine alkaloid N-oxides in pyrrolizidine alkaloid-containing natural products using HPLC-MS analysis

Pyrrolizidine alkaloid (PA)-containing plants are widely distributed in the world. PAs are hepatotoxic, affecting livestock and humans. PA N-oxides are often present together with PAs in plants and also exhibit hepatotoxicity but with less potency. HPLC-MS is generally used to analyze PA-containing herbs, although PA references are unavailable in most cases. However, to date, without reference standards, HPLC-MS methodology cannot distinguish PA N-oxides from PAs because they both produce the same characteristic ions in mass spectra. In the present study, the mass spectra of 10 PA N-oxides and the corresponding PAs were systemically investigated using HPLC-MS to define the characteristic mass fragment ions specific to PAs and PA N-oxides. Mass spectra of toxic retronecine-type PA N-oxides exhibited two characteristic ion clusters at m/z 118-120 and 136-138. These ion clusters were produced by three unique fragmentation pathways of PA N-oxides and were not found in their corresponding PAs. Similarly, the nontoxic platynecine-type PA N-oxides also fragmented via three similar pathways to form two characteristic ion clusters at m/z 120-122 and 138-140. Further application of using these characteristic ion clusters allowed successful and rapid identification of PAs and PA N-oxides in two PA-containing herbal plants. Our results demonstrated, for the first time, that these characteristic ion clusters are unique determinants to discriminate PA N-oxides from PAs even without the availability of reference samples. Our findings provide a novel and specific method to differentiate PA N-oxides from PAs in PA-containing natural products, which is crucial for the assessment of their intoxication.     

Analysis of cyclic boronated and trimethylsilylated phenolalkylamines by gas chromatography and electron impact mass spectrometry

The side chain of phenolalkylamines containing a bifunctional group was derivatized as the cyclic boronate, and then the residual phenolic group was trimethylsilylated. The resulting derivatives were single reaction products in each case, with good gas chromatographic properties and informative mass spectra to afford prominent molecular ions by gas chromatography with electron impact mass spectrometry (GC/EI-MS). The cyclic boronated-trimethylsilylated derivatives yielded the isotope pattern for boron ((10)B:(11)B =-1:4.2) and characteristic ions [M](+), [M - H](+), [M - CH(3)](+), [M - RBO](+), [M - TMSO](+), and [M - TMSO - C(6)H(5)](+) ions in the mass spectra. In order to distinguish between m- and p-phenolalkylamines, the mass spectra of the cyclic phenylboronated-trimethylsilylated (PBA-TMS) derivatives were compared with those of the trimethylsilylated (TMS) derivatives. The TMS derivatives of octopamine (p-) and norfenefrine (m-) showed identical mass spectra, while the PBA-TMS derivatives had mass spectra sufficiently different from one other to distinguish between the isomers. The most prominent ion of the PBA-TMS derivative is the [M - H](+) ion (m/z 310) for octopamine and the [M](+) ion (m/z 311) for norfenefrine. Copyright 1999 John Wiley & Sons, Ltd.     

13-乙酰基-9-甲基-11-羰基-8-氧代-10,12-二氮杂三环[7.3.1.02,7]十三碳-2,4,6-三烯的一锅煮合成和结构表征

描述了一种有效的环境友好的“一锅煮”法合成13-乙酰基-9-甲基-11-羰基-8-氧代-10,12-二氮杂三环[7．3．1．0~(2,7)]十三碳-2,4,6-三烯。该法用廉价易得的溴化镁作催化剂,在无溶剂存在下,由起始原料水杨酸,乙酰丙酮和脲通过Biginelli缩合反应伴随着分子内的Michael加成反应一步完成。用核磁共振氢谱、碳谱、飞行时间质谱以及红外光谱数据表征了产物的结构为一氧桥多环化合物,而不是带有自由羟基的二氢嘧啶酮。最后由质谱给出的精确质量及其所代表的元素组成推出了该化合物的质谱裂解途径。     

Metastable ions in the mass spectrum of uranium hexafluoride

A high content (about 0.3%) of metastable ions is detected in the mass spectrum of uranium hexafluoride (UF₆). The apparent masses of the metastable ions found from the masses of UF₆ fragment ions, which were taken as references, are close to values predicted (the discrepancy is no more than 0.015 u). It is shown that these ions are responsible for the background current in a wide mass range. The lifetime of a UF₅ metastable ion with a mass of 333 is estimated.     

Analysis of t-butylphenol acetylene condensed resin with methyl-methine linkages in vulcanized rubber by pyrolysis-gas chromatography/mass spectrometry

Methyl-methine linkages of Novolac, a commercially available t-butylphenol acetylene condensed (TBPA) resin, have been identified by recognition of pyrolysis pathways using pyrolysis-gas chromatography/mass spectrometry (Py-GC/mS) in vulcanized rubber. The diagnostic mass spectrum of t-butylphenol with methyl-methine linkages between phenolic rings was observed at m/z 192, corresponding to 4-t-butyl-2-ethyl-6-methylphenol. Other molecular ions were observed at m/z 178, 164, and 150 in the characteristic pyrolyzates. The ion at m/z 192 in the TBPA resin was observed to be characteristic for methyl-methine linkages between the phenolic groups, and the analytical pyrolysis-GC/mS method was thus able to identify the resin at low levels in vulcanized rubber. Copyright 1999 John Wiley & Sons, Ltd.     

Differentiation of aminomethyl corrole isomers by mass spectrometry

Two new isomeric aminomethyl corrole derivatives of [5,10,15-tris(pentafluorophenyl)corrolato]gallium(III) were synthesized with pyridine (py) molecules as axial ligands. When investigated by electrospray ionization mass spectrometry, in the positive and the negative ion modes, these compounds showed an unusual gas-phase behavior that could be used for their differentiation. In the positive ion mode, the differentiation was achieved through the formation of diagnostic fragment ions formed from [M-py?+?H](+) precursors, by (CH(3) )(2) NH and HF losses. An unusual addition of water to the main fragment ions provides an alternative route for isomer identification. Semi-empirical calculations were performed to elucidate the structures and stabilities of the main ionic species formed in the positive ion mode. In the negative ion mode isomer discrimination is accomplished via the fragmentation of the methoxide adduct ions [M-py?+?CH(3) O](-) through (CH(3) )(2) N(.) and HF losses.     

Ultrahigh resolution mass spectrometry and accurate mass measurements for high-throughput food lipids profiling

In the present study, accurate mass measurements by ultrahigh resolution mass spectrometry with Orbitrap-Exactive working at resolving power R: 100,000 (m/z 200, full width at half maximum) with an accuracy better than 2?ppm in all the mass range (m/z 200 to 2000) were used to show a detailed molecular composition of diverse edible oils and fats. Flow injection was used to introduce samples into the mass spectrometer, obtaining a complete analysis of each sample in less than 10 min, including blanks. Meticulous choice of organic solvents and optimization of the ion source and Orbitrap mass analyzer parameters were carried out, in order to achieve reproducible mass spectra giving reliable elemental compositions of the lipid samples and to prevent carry over. More than 200 elemental compositions attributable to diacylglycerols, triacylglycerols (TAGs), and their oxidation products have been found in the spectra of food lipids from different origin. Several compounds with very close molecular mass could only be resolved through ultrahigh resolution, allowing detailed and robust TAG profiling with a high characterization potential. Copyright ? 2012 John Wiley & Sons, Ltd.     

Optimization of a quadrupole ion storage trap as a source for time-of-flight mass spectrometry

Designs of a quadrupole ion trap (QIT) as a source for time-of-flight (TOF) mass spectrometry are evaluated for mass resolution, ion trapping, and laser activation of trapped ions. Comparisons are made with the standard hyperbolic electrode ion trap geometry for TOF mass analysis in both linear and reflectron modes. A parallel-plate design for the QIT is found to give significantly improved TOF mass spectrometer performance. Effects of ion temperature, trapped ion cloud size, mass, and extraction field on mass resolution are investigated in detail by simulation of the TOF peak profiles. Mass resolution (m/Δm) values of several thousand are predicted even at room temperature with moderate extraction fields for the optimized design. The optimized design also allows larger radial ion collection size compared with the hyperbolic ion trap, without compromising the mass resolution. The proposed design of the QIT also improves the ion-laser interaction volume and photon collection efficiency for fluorescence measurements on trapped ions.     

脉冲等离子体飞行时间质谱诊断技术

根据脉冲等离子体关键特征参数的特点及相关应用需求,基于垂直引入式有网反射二阶空间聚焦技术,研发了脉冲等离子体飞行时间质谱诊断系统,其质量分辨率约为1690(FWHM),离子能量诊断范围为3~150eV,时间分辨率约为0.45μs。通过对典型脉冲等离子体开展飞行时间质谱分析和研究,获得了离子质谱、离子能量分布函数等重要特征参数。等离子体以不同价态的Ti离子为主,Ti+最可几能量约为23eV,Ti 2+最可几能量约为48eV。     

Gas-flow assisted ion transfer for mass spectrometry

Methods and devices that use gas flows to collect ions and transfer them over long distances for mass spectrometric analysis have been developed. Gas flows derived from the ionization source itself or provided by means of additional pumping were used to generate a laminar flow inside cylindrical tube. Hydrodynamic simulations and experimental tests demonstrate that laminar flow can transfer ions over long distance. The typical angular discrimination effects encountered when sampling ions from ambient ionization sources are minimized, and the sampling of relatively large surface areas is demonstrated with desorption electrospray ionization (DESI). Ion transfer over 6 m has been achieved and its application to multiplexed chemical analysis is demonstrated on samples at locations remote from the mass spectrometer.     

Formation of oligomeric alkenylperoxides during the oxidation of unsaturated fatty acids: an electrospray ionization tandem mass spectrometry study

This study reports the identification of oligomeric alkenylperoxides by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS(2)), during the oxidation of oleic, linoleic and linolenic acids with Fenton's (Fe(2+)/H(2)O(2)) and Fe(2+)/O(2) systems. The reactions were followed by ferrous oxidation-xylenol orange method together with GC-MS and GC-FID, allowing to observe that both oxidation systems are different in terms of hydroperoxide evolution, probably due to the presence of different intermediate reactive species: perferryl ion and OH(·) radical responsible for the decomposition of lipid hydroperoxides and formation of new compounds. The analysis of ESI-MS in the negative mode, obtained after oxidation of each fatty acid, confirmed the presence of the monomeric oxidation products together with other compounds at high mass region above m/z 550. These new ions were attributed to oligomeric structures, identified by the fragmentation pathways observed in the tandem mass spectra.     

Identification of a Suspicious Drug by Using Spectroscopic Techniques: A Forensic Analytical Chemistry Project

We identified a drug analog by using screening and confirmatory tests. Total ion chromatogram showed a major peak with a molecular ion of 190 m/z, but no mass spectrum match from the NIST library. A minor peak was identified as 1-benzylpiperazine (molecular ion = 176 m/z). Molecular ions of both peaks differed by 14 m/z units, suggesting a –CH₂ – group. Both peaks had the same base peak of 91 m/z. Derivatizing the drug analog with trifluoroacetic anhydride confirmed the presence of 1-benzylpiperazine. No reaction occurred with the major peak. We proposed a benzyl-4-methylpiperazine structure, which was confirmed by NMR studies.     

紫外激光作用下环氧乙烷的TOF质谱研究

本文采用超声分子束技术,分别在308nm和355nm的紫外激光下,对环氧乙烷分子进行了多光子电离飞行时间(TOF)质谱研究.在308nm激光作用时,观测到C_2H_4O~+、C_2H_3O_+、CHO~+和CH_3~+等离子的信号;在355nm激光作用时,则没有观测到分子离子的信号.在两种激光作用下最强的信号都是CHO~+.但是两种激光下各碎片离子信号的光强指数有一定差别,表明在两种情形下,环氧乙烷分子经历了不同的电离解离过程.     

Effect of nitro groups and alkyl chain length on the negative ion tandem mass spectra of alkyl 3-hydroxy-5-(4'-nitrophenoxy) and alkyl 3-hydroxy-5-(2', 4'-dinitrophenoxy) benzoates

Tandem mass spectrometric behaviour was studied for a small combinatorial library of alkyl 3-hydroxy-5-(4'-nitrophenoxy) benzoates (A1-A5) and alkyl 3-hydroxy-5-(2', 4'-dinitrophenoxy) benzoates (B1-B5). The spectra were recorded by negative ion electrospray low-energy collision induced dissociation (CID) tandem mass spectrometry. The product ion spectra of [M - H](-) of the benzoates A1-A5 are similar, as are those of benzoates B1-B5. However, the spectra of the B series compounds differ significantly from those of the A series owing to the second electron-withdrawing nitro substituent in the B compounds. In addition, the length of the alkyl chain has an effect on the fragmentation. However, both series of compounds exhibit an abundant nitrophenoxy ion formed by the loss of 3-hydroxybenzoate. This is at m/z 138 in A1-A5 and at m/z 183 in B1-B5. A precursor ion scan of the nitrophenoxy ion provides a rapid method to identify the synthesised compounds in this type of combinatorial mixture. Copyright 1999 John Wiley & Sons, Ltd.     

飞行时间质谱峰值的漂移

飞行时间质谱仪(time-of-flight mass spectrometer, TOF-MS)在分子团簇的激光电离/解离动力学研究中广泛使用。文章报道了在用脉冲355 nm的YAG激光进行水/甲醇二元团簇的多光子电离研究中,发现在电离激光相对于脉冲分子束的不同延时下,即激光作用于脉冲束的不同位置,飞行时间质谱仪测得的离子的质谱峰值发生漂移。在激光作用于脉冲束的中段时,离子的信号最强,同时离子的峰值漂移达到最大。分析认为：这种峰值漂移不是因为新质量数谱峰的出现,而是离子在穿越质谱仪的离子引出区和加速区极板时发生部分离子吸附,引起极板间电压的起伏造成的。离子在电场起伏下的数值模拟与实验中观测到的离子峰值漂移规律一致。