An online ultra-high sensitivity Proton-transfer-reaction mass-spectrometer combined with switchable reagent ion capability (PTR + SRI − MS)

Proton-transfer-reaction mass-spectrometry (PTR-MS) developed in the 1990s is used today in a wide range of scientific and technical fields. PTR-MS allows for real-time, online determination of absolute concentrations of volatile (organic) compounds (VOCs) in air with high sensitivity (into the low pptv range) and a fast response time (in the 40–100 ms time regime). Most PTR-MS instruments employed so far use an ion source consisting of a hollow cathode (HC) discharge in water vapour which provides an intense source of proton donor H₃O⁺ ions. As the use of other ions, e.g. NO⁺ and O₂⁺, can be useful for the identification of VOCs and for the detection of VOCs with proton affinities (PA) below that of H₂O, selected ion flow tube mass spectrometry (SIFT-MS) with mass selected ions has been applied in these instances. SIFT-MS suffers, however, from at least two orders lower reagent ion counts rates and therefore SIFT-MS suffers from lower sensitivity than PTR-MS.Here we report the development of a PTR-MS instrument using a modified HC ion source and drift tube design, which allows for the easy and fast switching between H₃O⁺, NO⁺ and O₂⁺ ions produced in high purity and in large quantities in this source. This instrument is capable of measuring low concentrations (with detection limits approaching the ppqv regime) of VOCs using any of the three reagent ions investigated in this study. Therefore this instrument combines the advantages of the PTR-MS technology (the superior sensitivity) with those of SIFT-MS (detection of VOCs with PAs smaller than that of the water molecule and the capability to distinguish between isomeric compounds).We will first discuss the setup of this new PTR+SRI-MS mass spectrometer instrument, its performance for aromates, aldehydes and ketones (with a sensitivity of up to nearly 1000 cps/ppbv and a detection limit of about several 100 ppqv) and finally give some examples concerning the ability to distinguish structural isomeric compounds.     

Formation of vinylidene and vinylene by selective reactivity of Si(1 0 0)2 × 1 towards iso, cis and trans isomers of dichloroethylene

The room temperature (RT) chemisorption of three (iso, cis and trans) isomers of dichloroethylene (DCE) on Si(1 0 0)2 × 1 have been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Unlike ethylene, the lack of molecular desorption features in the TPD data effectively rules out the cycloaddition adsorption mechanism for all three isomers. XPS spectra show that cis- and trans-DCE adsorb dissociatively on the 2 × 1 surface in equal proportion as mono-σ bonded 2-chlorovinyl and di-σ bonded vinylene adspecies, which could be produced by dechlorination mechanisms involving the proposed tri-atom π-complex and diradical intermediates, respectively. Acetylene (m/z 26) evolution from 2-chlorovinyl adspecies at 590 K and vinylene at 750 K are also observed for both cis- and trans-DCE, further confirming the common adsorption mechanisms for these geometrical isomers and the relative stabilities of the adspecies. In contrast, only vinylidene adspecies is found for iso-DCE, which indicates that the high ionicity of the CCl₂ group favours the diradical dechlorination mechanism. The single m/z 26 desorption peak for iso-DCE adspecies observed at a higher temperature (780 K) than cis and trans isomers is consistent with the higher adsorption energy of vinylidene than vinylene on Si(1 0 0) obtained in our ab initio calculations. The different relative locations of the Cl atoms in these isomers therefore play a crucial role in controlling the adsorption and thermal evolution on Si(1 0 0)2 × 1. The selective reactivity of the 2 × 1 surface towards these isomers can be used to generate vinylene or vinylidene templates from their corresponding adspecies.     

Three isomeric copper(II) coordination polymers based on a bis-triazole-bis-amide ligand: Assembly,structures, and luminescent properties

Three copper(II) isomers, [Cu(dtcd)(DNBA)₂]_n (1–3) (HDNBA = 3,5-dinitrobenzoic acid, dtcd = N,N-di(4H-1,2,4-triazole)cyclohexane-1,4-dicarboxamide), were synthesized in a one-pot reaction, and structurally characterized. Polymer 1 shows a 1-D single chain in which dtcd connect adjacent Cu²⁺ ions, while DNBA^? is monodentate. In 2, every two Cu²⁺ ions are linked by carboxylate of a DNBA^? in a chelate-bridging mode into a binuclear unit, which is further connected by dtcd ligands into a 1-D double chain. In 3, dtcd connect Cu²⁺ ions via triazole nitrogens to generate 1-D single chains, which are further extended into a 2-D network by the amide oxygens of a dtcb from an adjacent chain. The pH plays an important role in product distribution of 1–3. The coordination behaviors of dtcd and DNBA^? also influence the final structures. Luminescent properties of 1–3 have been investigated.     

拓扑指数在预测氯代苯同分异构体的色谱保留值中的应用

采用三阶分子连接性指数计算分子有效表面积参数和有效体积参数，从而使ＵＮＩＦＡＣ基团贡献法能关联和预测氯代苯同分异构体的色谱保留值，实验值与预测值的相对误差小于１０％。     

雷酸家族史话

This article describes an introduction of fulminic acid. The story of fulminic acid and fulminates was introduced from the discovery of mercury fulminate to the concept of isomers and the success of Alfred Nobel in the development of explosives. This process provides a good example of integrating science and technology.     

有机异构体的质谱分析简介

本文介绍了用于有机异构体辨析的几种质谱方法，并综述了它们在五类异构体中的应用。     

C70S可能异构体的结构与稳定性的理论研究

分别用半经验的AMl，PM3及MNDO方法研究了富勒烯衍生物C70S的12种可能异构体的结构和稳定性．计算结果表明：S原子加成在4种6-6键上的稳定构型中，非赤道带6-6键加成的三个异构体为闭环结构，赤道带6-6键加成的一个异构体为开环结构；S原子加成在4种6-5键上均可产生开环和闭环两种稳定构型．加成在6-5双键的异构体其闭环构型更稳定，加成在6-5单键的异构体其开环构型更稳定．闭环异构体中S原子加成在碳球极处6-6键上的构型1，2最稳定，开环异构体中S原子加成在赤道带6-6键上的构型8最稳定．     

High energy collision-induced dissociation (CID) product ion spectra of isomeric polyhydroxy sugars

High energy (4 keV) collision-induced dissociation (CID) product ion spectra have been obtained for a series of isomeric sugar molecules of close structural similarity. The reproducibility of the approach has been established and the spectra shown to have significant differences. These differences have been rationalised in terms of conventional mass spectrometric fragmentation rules. The data have also been subjected to analysis using chemometric methods, which require no specialist mass spectrometric input. The resulting classification of the data shows good agreement with the conventional interpretation approach.     

Separation of isomers of nitro-polycyclic aromatic hydrocarbons

Since positional isomers of several nitro-polycyclic aromatic hydrocarbons (nitro-PAH) contain widely different mutagenic properties, methods for separating the isomers were investigated. High performance liquid chromatography with dichloromethane in hexane on silica gave the best resolution for the majority of the compounds. A few groups of isomers were better resolved with other modifiers or with reversed phases. Of the reversed phase systems, methanol-water gave better resolution than acetonitrile-water. With dichloromethane/hexane on silica, the retention was found to depend on the presence of a bay nitro group (first), the number of H atoms peri to the nitro group (second), and the length/breadth ratio of the molecule (third). Front electron density calculations were combined with the structure-retention relations in making tentative structure assignments of minor isomers of nitro-PAH.     

Preparation and evaluation of OV-240-OH coated glass capillary columns for isomer specific determination of PCDDs and PCDFs

Glass capillaries were leached, dehydrated, persilylated with 1, 3-bis (3-cyanopropyl) tetramethyldisiloxane, and coated with OV-240-OH. After crosslinking and binding the phase to the glass surface the columns showed high separation efficiency, high temperature stability, and inertness comparable to persilylated apolar columns. Column performance is shown to be superior to liquid phase cyanopropyl columns such as SP 2330. The excellent separation capabilities together with the selectivity of the phase makes OV-240-OH coated columns a valuable tool for the determination of toxic isomers in complex mixtures of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). The order of elution of individual TCDD isomers was found to be similar to that described for SP 2330 or Silar 10c. The detection of PCDDs and PCDFs in a fly ash extract further illustrates the utility of OV-240-OH coated columns. The high temperature limit of these columns opens the way for the analysis of high boiling compounds such as mixed brominated/chlorinated dibenzo-p-dioxins and dibenzofurans.