大黄酸ESI-IT MS质谱行为及碎片离子的量子化学研究

采用电喷雾-离子阱质谱(ESI-IT MS),获取大黄酸分子的一级质谱和多级质谱碰撞诱导解离下的碎片离子,以量子化学计算大黄酸分子及其主要碎片离子的质谱行为。通过对质谱离子几何参数、键断裂能、电荷变化、自旋密度以及前线分子轨道的分析,可得到m/z 282.8、256.9、238.9、210.8、192.8、182.8、166.8离子的稳定构型以及质谱裂解途径,从而较系统地解释了大黄酸分子在ESI-IT MS中的裂解行为。     

Evidence for thermal decomposition contributions to the mass spectra of chlorinated phenoxyacid herbicides obtained by particle beam liquid chromatography mass spectrometry

The spectral quality of a group of chlorinated phenoxyacid herbicides has been shown to degrade under certain conditions upon introduction into the mass spectrometer by a particle beam interface. Experiments were performed to investigate these changes in spectra. Normalized ion chromatograms were generated for the herbicides, and the results showed a broadening of the profiles of some ions, indicating a longer residence time in the ion source. These ions were postulated as coming from the ionization of thermal degradation products from the herbicides. The generation of these ions was dependent on ion source temperature, analyte concentration, and, by implication, ion source cleanliness. Tandem mass spectrometry experiments were performed on these ions from the herbicides and ions from the corresonding phenols. The tandem mass spectra of the ions from the herbicides were similar to the tandem mass spectra of the ions from the phenols. Therefore, it appears that the particle beam mass spectra of the chlorinated phenoxyacid herbicides are composite spectra with contributions from the gas phase ionization of the parent herbidides and thermal decomposition products.     

碳氮二元簇离子的激光产生与碰撞诱导解离研究

以脉冲激光束在高真空中溅射铁氰化钾,产生了各种组成的碳氮原子簇负离子,记录了它们的飞行时间质谱。根据这些簇离子的碰撞诱导解离研究结果,推测了它们的结构,发现它们大都具有超共轭的稳定体系,它们的构型随成簇氮原子数的增加,从一维直链向二维芳环转化。     

Application of the statistical test of equivalent pathways (STEP) method to the triple quadrupole mass spectrometer

Recently, we demonstrated a new method, STEP (Statistical Test of Equivalent Pathways) analysis, which differentiates first-generation product ions (primary product ions) from second-generation product ions (secondary product ions) obtained in tandem mass spectrometric (MS/MS) experiments on a quadrupole ion trap mass spectrometer. The study presented here defines how to adapt the STEP method to a more routinely used mass analyzer, the triple quadrupole. New ion activation conditions were developed to adapt the STEP method to the triple quadrupole mass spectrometer using peptides and carbohydrates. The application of this method to the triple quadrupole is useful because it provides an efficient approach to differentiate primary and secondary ions on this instrument. Out of the total number of ions that were subjected to the STEP analysis, this method correctly identified 96% of ions as primary or secondary, indicating that this analysis is effective for carbohydrates and peptides undergoing collision-induced dissociation (CID) on a triple quadrupole mass spectrometer.     

Dissociative electron attachment to glycyl-glycine, glycyl-alanine and alanyl-alanine

The processes of negative ions formation of dipeptides glycyl-glycine, glycyl-alanine and alanyl-alanine in the conditions of resonant electron capture have been studied with a help of negative ions mass spectrometry. Using a thermochemical approach, the main channels of fragment negative ions formation were found and the structure of the ions were established. The isobaric ions have been identified by the experiments with high mass resolution. The cross sections of fragment ions formation were measured. The metastable fragmentation of [M-H](-) and [M-COOH](-) ions in the energy range 4.5-7.5 eV have been found.     

Electrospray ionization mass spectra of amino acid phosphoramidates of adenosine

Amino acid phosphoramidates of adenosine were synthesized and determined by positive and negative ion electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated. In the positive ion mass spectra abundant characteristic fragment ions appeared, and many complementary ions were found. In the negative ion mass spectra only a few fragment ions were observed, and most of them contained phosphoryl groups. The results show that ESI-MS is a useful tool for structural determination of amino acid phosphoramidates of nucleosides.     

Comparison of Triple Quadrupole and Double Focusing Mass Spectrometers to Investigate Collision-Induced Dissociation and Metastable Ions of Glycoconjugates

Glycoconjugates, such as chromophore-labeled disaccharides and permethylated glycosphingolipids (GSL) were used for comparison of triple quadrupole and double focusing mass spectrometers in analysis of product ions. A profound effect of collision energy was observed in the product ion spectra of ceramide ions (fragment ions of permethylated GSL): more product ions were observed from a double focusing mass spectrometer. Besides collision energy, the structure of the analyte had a significant effect on the formation of product ions. Despite the fact that masses of protonated molecular ions (MH⁺) of permethylated GSL are significantly larger than their ceramide fragments, the low-energy and high-energy product ion spectra of MH⁺ are, in general, similar. In a double focusing mass spectrometer of reversed geometry, more metastable ions were observed in the first field free region (FFR) than in the second FFR. The metastable ions observed in the second FFR were similar to those observed in low-energy collision-induced dissociation (CID). Although a double focusing mass spectrometer is superior to triple quadrupole instrument for detection of product ions, the poor resolution in either the selection of precursor ion or in the product ion spectra can be a serious problem in analysis of a mixture with similar masses.     

Doubly charged ion mass spectra. 7—acetylenes

Doubly charged ion mass spectra of 20 aliphatic and 3 aromatic acetylenic compounds have been measured using a double focusing Hitachi RMU-7L mass spectrometer. Spectra were obtained using 100 eV ionizing electron energy and 3.2 kV ion accelerating voltage. In general, the spectra of aliphatic type acetylenic compounds were dominated by fragment ions formed by extensive H loss from doubly charged molecular ions. Intense molecular ions were observed in the doubly charged ion spectra of phenyl-substituted acetylenes. Total product ion intensities for doubly charged ion spectra of acetylenic compounds were found to be smaller, in general, than the total product ion intensity observed in the benzene doubly charged ion mass spectrum. Measured appearance energies of intense product ions ranged from 24 to 47 eV. A geometry optimized quantum mechanical self-consistent field molecular orbital treatment was employed to compute energies and structural parameters of prominent ions in the doubly charged ion mass spectra of acetylenic compounds.     

Dual parallel electrospray ionization and atmospheric pressure chemical ionization mass spectrometry (MS), MS/MS and MS/MS/MS for the analysis of triacylglycerols and triacylglycerol oxidation products

Two mass spectrometers, in parallel, were employed simultaneously for analysis of triacylglycerols in canola oil, for analysis of triolein oxidation products, and for analysis of triacylglycerol positional isomers separated using reversed-phase high-performance liquid chromatography. A triple quadrupole mass spectrometer was interfaced via an atmospheric pressure chemical ionization (APCI) interface to two reversed-phase liquid chromatographic columns in series. An ion trap mass spectrometer was coupled to the same two columns using an electrospray ionization (ESI) interface, with ammonium formate added as electrolyte. Electrospray ionization mass spectrometry (ESI-MS) under these conditions produced abundant ammonium adduct ions from triacylglycerols, which were then fragmented to produce MS/MS spectra and then fragmented further to produce MS/MS/MS spectra. ESI-MS/MS of the ammoniated adduct ions gave product ion mass spectra which were similar to mass spectra obtained by APCI-MS. ESI-MS/MS produced diacylglycerol fragment ions, and additional fragmentation (MS/MS/MS) produced [RCO](+) (acylium) ions, [RCOO+58](+) ions, and other related ions which allowed assignment of individual acyl chain identities. APCI-MS of triacylglycerol oxidation products produced spectra like those reported previously using APCI-MS. APCI-MS/MS produced ions related to individual fatty acid chains. ESI-MS of triacylglycerol oxidation products produced abundant ammonium adduct ions, even for those molecules which previously produced little or no intact molecular ions under APCI-MS conditions. Fragmentation (MS/MS) of the [M+NH(4)](+) ions produced results similar to those obtained by APCI-MS. Further fragmentation (MS/MS/MS) of the diacylglycerol fragments of oxidation products provided information on the oxidized individual fatty acyl chains. ESI-MS and APCI-MS were found to be complementary techniques, which together contributed to a better understanding of the identities of the products formed by oxidation of triacylglycerols.     

Mass-spectrometric studies of new 6-nitroquipazines—serotonin transporter inhibitors

Six synthesized 6-nitroquipazine derivatives were examined by electron ionization (EI) and electrospray ionization (ESI) mass spectrometry in positive and negative ion mode. The compounds exhibit high affinity for the serotonin transporter (SERT) and belong to a new class of SERT inhibitors. The EI mass spectra registered in negative ion mode showed prominent molecular ions for all the compounds studied. All EI mass spectra and all ESI mass spectra showed similar fragmentation pathways of molecular ions, but the pathways differed between EI and ESI. The differences were explained with the aid of theoretical evaluation of the stability of the respective radical ions (EI MS) and protonated ions (ESI MS).     

Massenspektrometrische Untersuchungen an einigen Halogeniden der 5. Haupt- und Nebengruppe

The mass spectra of fifth group halids and some of their substitution products have been studied. Fragmentation processes, charge distributions as well as relative stabilities of fragment ions and double-charged ions are discussed. Appearance potentials have been measured and discussed, with reference to decomposition reactions and abundance considerations of fragment ions. In some cases polymeric ions were found in mass spectra.     

糖苷混合物FAB质谱分析技术的研究

我们曾阐明了糖苷单-化合物分子量的简明, 快速确定方法, 根据糖苷化合物中引入碱金属离子的FAB正离子的加合离子峰而难于找到碎片的加合离子峰, 现在我们在糖苷混合物中, 同时引入两种碱金属离子Na^+和Li(两元素原子量之差为16), 由此得到的糖苷混合物的FAB正离子谱中, 就出现两个一组的多组强峰, 且每组的两峰之质量差为16, 每组中低质量峰为[M+Li]^+峰, 高质量为[M+Li]^+峰, 根据两峰已标出的质量数便可轻易地定出各成分的分子量来。谱图中出现的强峰组数就是糖苷混合物的成分数。     

Accurate mass measurement at enhanced mass-resolution on a triple quadrupole mass-spectrometer for the identification of a reaction impurity and collisionally-induced fragment ions of cabergoline

In this study, accurate mass measurements were made by electrospray ionization (ESI) on a triple quadrupole mass spectrometer operating in enhanced mass-resolution mode (peak width = 0.1 u FWMH), to give qualitative information relating to the pharmaceutical, cabergoline. Accurate mass determinations by ESI-MS were performed on a protonated impurity formed during cabergoline storage. The accurate mass measurement resulted in only one proposed elemental composition for the impurity, using reasonable elemental limits and mass tolerance for the calculation. This information was sufficient to propose a structure for the impurity where ESI-MS/MS proved consistent. The difference between the accurate mass measurement and the exact mass calculated for the proposed structure was 0.8 mmu, with a standard deviation of 0.7 mmu for replicate accurate mass determinations. Accurate mass determinations in ESI-MS/MS provided information on cabergoline fragment ions formed through collisionally-induced dissociation. Since the potential formation of isobaric ions exists for two major cabergoline fragment ions, accurate mass measurement allowed for the determination of the most probable fragment ion structures. The differences between the accurate mass measurements and exact masses calculated for the proposed fragment ions were 1.9 and 2.1 mmu, with standard deviations of 0.4 and 0.8 mmu, respectively, for replicate determinations.     

调控微波等离子体能量进行药片活性分子结构的质谱分析

采用微波等离子体质谱(MPT-MS)技术,对替硝唑和马来酸氯苯那敏药片进行快速质谱分析.通过调控等离子体能量,在一级谱图中可得到目标物的准分子离子及丰富的碎片离子,这些碎片离子与其对应串联质谱数据基本一致,甚至更加丰富;结合标准品比对分析,最终确定这些碎片离子来自目标物而非基质.因此,MPT兼具硬电离和软电离性质,采用MPT-MS技术从一级质谱图中获得的数据可对药片中活性分子的结构进行鉴定.该方法具有快速、准确及环保等特点,在发展MPT与简单的质量分析器联用,实现质谱仪的小型化等方面有广阔的应用前景.     

Toward high pressure miniature protein mass spectrometer: Theory and initial results

Current miniature mass spectrometers mainly focus on the analyses of organic and small biological molecules. In this study, we explored the possibility of developing high resolution miniature ion trap mass spectrometers for whole protein analysis. Theoretical derivation, GPU assisted ion trajectory simulation, and initial experiments on home‐developed “brick” mass spectrometer were carried out. Results show that ion‐neutral collisions have smaller damping effect on large protein ions, and a higher buffer gas pressure should be applied during ion trap operations for protein ions. As a result, higher pressure ion trap operation not only benefits instrument miniaturization, but also improves mass resolution of protein ions. Dynamic mass scan rate and generation of low charge state protein ions are also found to be helpful in terms of improving mass resolutions. Theory and conclusions found in this work are also applicable in the development of benchtop mass spectrometers.     

Electrospray mass spectrometry: a study on some aqueous solutions of metal salts

Aqueous metal salt solutions were used as models to probe the origin of the species observed in the electrospray mass spectrum. A qualitative or semiquantitative correlation among different species was observed between electrospray responses and calculated equilibrium aqueous solution concentrations. Quantitative correlations were obtained, however, when ions that were identical in charge and similar in type were selected for comparison. In these experiments the ions experienced very similar electrospray-related processes and their effects on the responses were canceled in a comparison of these ions. Consequently, the relative abundances of these ions in the electrospray mass spectrum closely matched the calculated relative abundances in aqueous solution. Our results suggest that the basic principle that determines ionic distribution in the electro spray mass spectrum in aqueous solution chemistry.     

Why are electron capture negative ion mass spectra not reproducible? An ion source problem

Differences in the electron capture negative ion mass spectra of environmentally related organic compounds acquired on a VG 30-250 triple quadruple mass spectrometer and on an HP 5985B gas chromatography/mass spectrometry system were investigated with respect to the ion formation process. Neither ion source temperature nor pressure was responsible for the differences. The populations of thermal electrons in both ion sources were experimentally determined and found to be similar, suggesting that electron capturing reactions should proceed with comparable efficiencies in both ion sources. The ion extraction efficiencies of the two instruments were examined by monitoring the transmission profiles of low- and high-mass ions as a function of lens potentials. Results indicated that the HP 5985B extraction lens significantly suppressed low-mass ions. Further, theoretical evaluation of ion trajectories using SIMION suggested that on the HP 5985B, low-mass ions entered the mass analyzer as a defocused beam, but high-mass ions entered the analyzer as a well-collimated beam. On the VG 30–250, low- and high-mass ions were transmitted to the analyzer with equal efficiency by the ion extraction system.     

Investigations on cluster and molecular ion formation by plasma mass spectrometry

The formation of molecular and cluster ions of different inorganic materials in plasma mass spectrometry – spark source mass spectrometry (SSMS), radiofrequency glow discharge mass spectrometry (rf GDMS), laser ionization mass spectrometry (LIMS), inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) – was investigated and compared. Similar abundance distributions of cluster ions were observed for a graphite sample, for boron nitride/ graphite and for metal oxide/graphite mixtures using different plasma mass spectrometric methods. A correlation of intensities of metal argide ions in ICP-MS with their bond dissociation energies was used to estimate unknown dissociation energies of molecular ionic species. For the elements of the 2nd or 3rd period in the periodic table, the intensities of most argon molecular ions (ArX⁺) measured by ICP-MS rise with increasing atomic number in a similar manner to the theoretically calculated bond dissociation energies of argon molecular ions.     

Factors determining the performance of triple quadrupole, quadrupole ion trap and sector field mass spectrometers in electrospray ionization tandem mass spectrometry of oligonucleotides. 1. Comparison of performance characteristics

The performance of triple-stage quadrupole (TSQ), quadrupole ion trap (QIT), and double focusing sector field (DFSF) mass spectrometers for the generation of fragment ions to obtain sequence information about oligonucleotides was compared. Upon electrospray ionization (ESI), the charge-state distribution of candidate precursor ions not only varied significantly with the type of mass spectrometer, but also with the size and sequence of the investigated oligonucleotides. While concentration limits of detection for an octanucleotide were in the 100 pmol/L range on the QIT and in the 5-10 nmol/L range on the TSQ and DFSF instruments, those of a 24-mer were in the 2-13 nmol/L range on all three instruments. Reproducibility of mass determination, an important prerequisite for reliable identification of fragment ions, was highest on the TSQ with 0.0037% relative standard deviation over three days. Finally, the tandem mass spectra of a dimethoxytritylated pentanucleotide recorded on the three instruments were compared. Relatively simple spectra dominated by complete series of fragment ions of the (a-B) and w type were obtained on the QIT. Complete series of (a-B) and w ions were also observed on the TSQ. However, additional fragments belonging to the b, c, d, x and z series were found in the spectrum. In the spectrum recorded after in-source fragmentation in the DFSF, only fragments corresponding to the loss of a nucleobase and a complete series of w ions were observed. All three mass spectrometers were suitable for the generation of fragment ions, from which the complete nucleotide sequence of the pentanucleotide could be deduced.     

A comparison of electron ionization mass spectra obtained at 70 eV,low electron energies,and with cold EI and their NIST library identification probabilities

Electron ionization (EI) mass spectra of 46 compounds from several different compound classes were measured. Their molecular ion abundances were compared as obtained with 70‐eV EI, with low eV EI (such as 14 eV), and with EI mass spectra of vibrationally cold molecules in supersonic molecular beams (Cold EI). We further compared these mass spectra in their National Institute of Standards and Technology (NIST) library identification probabilities. We found that

1. Low eV EI is not a soft ionization method, and it has little or no influence on the molecular ion relative abundances for large molecules and those with weak or no molecular ions.
2. Low eV EI for compounds with abundant or dominant molecular ions in their 70 eV mass spectra results in the reduction of low mass fragment ions abundances thereby reducing their NIST library identification probabilities thus rarely justifies its use in real‐world applications.
3. Cold EI significantly enhances the relative abundance of the molecular ions particularly for large compounds; yet, it retains the low mass fragment ions; hence, Cold EI mass spectra can be effectively identified by the NIST library.
4. Different standard EI ion sources provide different 70 eV EI mass spectra. Among the Agilent technologies ion sources, the “Extractor” exhibits relatively abundant molecular ions compared with the “Inert” ion source, while the “High efficiency source” (HES) provides mass spectra with depleted molecular ions compared with the “Inert” ion source or NIST library mass spectra.

These conclusions are demonstrated and supported by experimental data in nine figures and two tables.