Towards the electrospray ionization mass spectrometry ionization efficiency scale of organic compounds

An approach that allows setting up under predefined ionization conditions a rugged self-consistent quantitative experimental scale of electrospray ionization (ESI) efficiencies of organic compounds is presented. By ESI ionization efficiency (IE) we mean the efficiency of generating gas-phase ions from analyte molecules or ions in the ESI source. The approach is based on measurement of relative ionization efficiency (RIE) of two compounds (B1 and B2) by infusing a solution containing both compounds at known concentrations (C1 and C2) and measuring the mass-spectrometric responses of the protonated forms of the compounds (R1 and R2). The RIE of B1 and B2 is expressed as logRIE(B1, B2) = log[(R1 . C2)/(C1 . R2)]. The relative way of measurement leads to cancellation of many of the factors affecting IE (ESI source design, voltages in the source and ion transport system, solvent composition, flow rates and temperatures of the nebulizing and drying gases). Using this approach an ESI IE scale containing ten compounds (esters and aromatic amines) and spanning over 4 logRIE units has been compiled. The consistency of the scale (the consistency standard deviation of the scale is s = 0.16 logRIE units) was assured by making measurements using different concentration ratios (at least 6-fold concentration ratio range) of the compounds and by making circular validation measurements (the logRIE of any two compounds was checked by measuring both against a third compound).     

Ferrocene modification of organic compounds for medicinal applications

The results of the authors on the synthesis of ferrocene-containing organic compounds obtained in 1998–2013 are summarized. The review is focused on the ferrocene modifications of purine and pyrimidine bases, thiopyrimidines, natural and synthetic amino acids, azoles (including polyfluoroazoles and mercaptoazoles) and ferrocenyl quinoline synthesis. The special attention is given to the scale synthesis of compounds for biological trials.     

Surface charge spectroscopy and its applications

Surface Charge Spectroscopy (SCS) is a surface sensitive technique for measuring potential distributions across an ultrathin (<100Å) insulator/semiconductor structure. Although the applicability of the technique is rather narrowly confined to such a specific sample structure, SCS bears considerable industrial significance because insulator/semiconductor structures are the most commonly used functional elements in microelectronics, and because gate insulators used in the industry are indeed getting to a nanometer thickness scale. The basic SCS concept relies on the measurements of the potential energies of electronic states using the conventional photoemission spectroscopic method, energy data which bear the information of the electrical potential gradient across the probed surface region. Surface sensitivity of SCS is thus contained in the framework of photoemission spectroscopy. Unlike conventional photoemission studies, SCS always measures the potential gradients corresponding to a specific surface potential. In fact, its analytical power is only shown when the surface potential of a sample can be controlled, and coincidentally an insulator/semiconductor device structure in microelectronics is only functional when the potential gradient extending into the semiconductor region can be changed effectively by the surface potential of the insulator. When SCS data are examined beyond the simple space-charge model commonly employed by electrical characterisation techniques like capacitance-voltage measurements, they can give information other than the relationship between the insulator surface potential and semiconductor surface potential (and thus interface state distributions across the bandgap of the semiconductor). Rather, they also provide unique information on the depth distributions of various types of fixed charges in the sample structure at an atomic level, and on the insulator breakdown mechanisms.     

Spectrophotometric determination of ionization constants of some organic compounds in aqueous solution

Ionization constants of some phenols and anilines in aqueous solution with a ionic strength of 0.01 were measured at 25°C by spectrophotometric method. The set of substrates was selected on the basis of the results of preliminary calculations of ionization constants in terms of an elemental linear empirical approach with account taken of the lack of the corresponding consistent published data.     

Electrolytic partial fluorination of organic compounds. 83. Anodic fluorination of N-substituted pyrroles and its synthetic applications to gem-difluorinated heterocyclic compounds

Anodic fluorination of N-substituted pyrroles was carried out in MeCN containing supporting fluoride salts such as Et3N-nHF (n = 2-5) and Et4NF-4HF with use of platinum electrodes under constant current conditions. Anodic fluorination of N-methyl- and N-p-tosylpyrroles having an electron-withdrawing cyano group proceeded smoothly to provide the corresponding fluorinated products in moderate to excellent yields, while anodic fluorination of N-methylpyrrole devoid of an electron-withdrawing cyano group did not take place and a polymeric product was formed at the anode surface. In sharp contrast to the cases of N-methylpyrroles, even N-p-tosylpyrrole devoid of an electron-withdrawing cyano group underwent anodic fluorination efficiently. Diels-Alder reaction of 5,5-difluoro-1-methyl-3-pyrrolin-2-one (2e) derived from anodic fluorination of 2-cyano-1-methylpyrrole (2a) with various dienes was carried out to provide the cycloaddition products in excellent yields. Furthermore, Michael reaction of 2e with various nucleophiles was also successfully carried out to provide the Michael addition products in good to excellent yields.     

Modern methods for estimation of ionization constants of organic compounds in solution

The review considers main up-to-date approaches to the calculation of ionization constants of organic compounds in solutions. Methods based on quantum-chemical calculations, continuum solvent models, cluster models, and quantitative structure-property relationships are discussed. The results of calculations of pK _a values by different methods, obtained in the past decade, are compared.     

Field ionization studies of unstable organic compounds with a double focusing mass spectrometer

Zusammenfassung Die Feldionisation einer Reihe instabiler organischer Verbindungen wurde mit einem doppeltfocussierenden Massenspektrometer unter Benutzung einer neuen kombinierten Feldionisations/Elektronenstoß-Ionenquelle bei direkter Probenzuführung untersucht. Das maximale Auflösungsvermögen m/m betrug etwa 30000. Leistungsdaten der Ionenquelle und Analysenergebnisse werden mitgeteilt. Im Gegensatz zur Elektronenstoßionisation wurden bei der Feldionisation in allen Fällen Molekülionen gefunden. Die Ergebnisse zeigen, daß die Feldionisation vorteilhaft für Molekulargewichtsbestimmungen und Strukturuntersuchungen instabiler hochmolekularer Verbindungen eingesetzt werden kann.

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Summary Field ionization of several unstable compounds has been studied with a double focusing mass spectrometer of high resolving power using a combined field ionization/electron impact ion source in connection with a direct inlet probe. A maximum resolving power with field ionization of more than 30,000 was attained. The performance data of the ion source are given. The results show that field ionization indeed enables molecular weight determinations and structure investigations of unstable high molecular weight compounds.

     

Photoelectron resonance capture ionization mass spectrometry: a soft ionization source for mass spectrometry of particle-phase organic compounds

Photoelectron resonance capture ionization (PERCI) is a soft and sensitive ionization method, based on the attachment of low-energy (<1 eV) photoelectrons to organic analyte molecules. PERCI has been developed in our laboratory for the real-time analysis of organic particles by mass spectrometry, and is employed here to monitor the heterogeneous reaction of ozone with oleic acid. Simplified identification of the reaction products is possible as a result of the soft nature of PERCI, giving predominantly the [M--H](-) ions. The major particle-phase products are identified as: 1-nonanal, nonanoic acid, 9-oxononanoic acid, and azelaic acid, consistent with proposed mechanisms. New insight into this well-studied heterogeneous reaction is gained as additional minor particle-phase products, consistent with the Criegee mechanism, are readily detected.     

Low-temperature plasma ionization source for the online detection of indoor volatile organic compounds

A simple-structure, low-power, and low-cost low temperature plasma (LTP) ionization source, coupled with mass spectrometry, for the online detection of indoor volatile organic compounds (VOCs) has been constructed in this work. Air, instead of noble gases, was employed as the discharging and carrier gas. And a custom-built AC high-voltage power supply with a total power consumption of 5 W, frequency of 2-4 kHz, and amplitude around 1-5 kV_p-p was used. This LTP source is a soft ionization source. The initial performance of the ionization source has been evaluated by ionizing samples including alcohols, ketones, aldehydes and aromatics. These compounds cover most of the common air pollutants concerning people's health. It is well known that those plasmas generated by dielectric barrier discharge (DBD) produce significant amount of metastable species and electrons with mean energies greater than several electronvolt, but minimal fragmentation was observed in our work. Protonated ions are the dominant product for the VOCs detected after the ionization process. Further work has been conducted to confirm the detection feature of this source. The results are promising enough to ensure the novel LTP ionization source as an effective tool for the online detection of indoor VOCs.     

大气有机物热脱附-全二维气相色谱-火焰离子化分析方法

全二维气相色谱（GC×GC）是20世纪90年代发展起来的具有高分辨率、高灵敏度、高峰容量等优势的分离技术,在我国将其用于大气挥发性有机物（VOCs）研究方面才刚刚起步.本文将GC-GC与氢火焰离子化检测器（FID）联用,构建了用于测量大气有机物的热脱附-全二维气相色谱-氢火焰离子化分析系统（TD-GC×GC-FID）.采用HP-5MS和HP-INNOWAX色谱柱,建立了C5-C15大气有机物分析方法,实现了一次分析过程同时分离非甲烷烃（NMHCs）、含氧挥发性有机物（OVOCs）和卤代烃等多种组分.利用标准物质和四级杆质谱（qMS）进行定性,外标法结合FID质量校正因子定量.目标物在GC-GC谱图中第一和第二维保留时间变化分别小于0.6s和0.02s,峰体积平均相对标准偏差为14.3%,其中烷烃和芳香烃为4.5%.标准曲线r2均值大于0.99,平均检出限为6.04ng,平均回收率为111%.利用该方法检测到2010年1月北京市区大气中400多种有机物（信噪比大于50）,鉴定了其中的103种物质,包括烷烃、烯烃、芳香烃、卤代烃、醛、酮、酯、醇和醚等.所测定有机物平均总浓度为51.3×10-9V/V,其中OVOCs约占51%,芳香烃约占30%,烷烃约占15%,卤代烃和烯烃分别占3%和1%.平均浓度最高的前3个组分是乙醇（9.84×10-9V/V）、丙酮（6.72×10-9V/V）和甲苯（3.48×10-9V/V）.     

Electrospray/VUV single-photon ionization mass spectrometry for the analysis of organic compounds

For the comprehensive analysis of organic compounds, especially thermal labile and nonpolar compounds, an electrospray/vacuum ultraviolet (VUV) single-photon ionization (ES-SPI) method was developed. The fine droplets of the sample solution from the electrospray process were directed through a quartz capillary and two skimmers to form a molecular beam into a high vacuum ionization chamber. The neutral sample molecules were softly ionized with tunable VUV light and analyzed with a reflection time-of-flight mass spectrometer (RTOF-MS). The ionization energy (IE) and appearance onsets of fragments were obtained based on the photoionization efficiency (PIE) spectrum. The isomers can also be distinguished. With this new method, clean (fragment-free) mass spectra of nonpolar compounds, such as benzene, cyclohexane, and some thermal labile solid compounds (triphenylamine, thioacetamide, and urea) have been obtained without any tedious pretreatment. The components of complex mixtures (gasoline and kerosene) can be identified. Furthermore, quantitative analysis of the components can be obtained based on photoionization cross section data. This method may be used for quantitative analysis of small biomolecules and natural products.     

Solid state chemical ionization for characterization of organic compounds by laser mass spectrometry

A new technique involving the addition of a compound to the analyte to serve as a source of "reagent" ions has been developed for negative-ion laser mass spectrometry. This "solid state chemical ionization" leads to ions characteristic of the analyte, owing to ion-molecule reactions between the "reagent" ion and the neutral analyte in the laser-generated plume. Polycyclic aromatic hydrocarbons show formation of an ion corresponding to (M + O - H)(-) in their negative-ion laser mass spectra when mixed with compounds such as sym-trinitrobenzene, sodium nitrate and sodium peroxide. NO(-)(2), O(-), and O(-)(2) serve as "reagent" ions in these compounds. Formation of (M + Cl)(-) is seen in the laser mass spectra of glycosides mixed with hexachlorobenzene. Chloride serves as the "reagent" ion in this case.     

有机同秩物概念及单取代烷烃同秩物生成焓和电离能变化规律

提出了“有机同秩列”、“有机同秩物”、“有机同秩异构体”等概念体系,并以单取代烷烃同秩物Xi-（CH2）/-H（Xi=F、CI、Br、I、NO2、CN、NC、OH、NH2、SH、COOH、CHO）为例,对其气相标准摩尔生成焓（△rHm）、电离能（IP）的结构-性能关系进行了研究,分别对j=2～8的七组同秩物的生成焓及j=2～4的三组同秩物的电离能建立了数学模型：△rHm（j）=a＋b△iHm（1）＋cPEI（R）和IP（j）：a＋bIP（1）＋bPEI（R）,得到了有意义的结果．研究表明,从有机同秩物的角度可以建立一种新的分子结构．性能相关方法,它与有机同系物方法相互独立又互为补充．本文提出的概念体系不仅增加了新的有机化学理论和概念,还为有机物结构-性能变化规律的研究开辟了新视角．     

Development of soft plasma ionization (SPI) source for analysis of organic compounds

We present a newly designed soft plasma ionization (SPI) source developed for mass spectrometric study of organic compounds in this study. The SPI cell having a relatively small size consists of a hollow anode and a hollow mesh cathode. The voltage–current characteristic depending on the pressure was investigated, indicating that it has similar characteristics to conventional hollow cathode glow discharges. To investigate the emission characteristics of the SPI source, some molecular band emission spectra (N₂, N₂⁺ and OH⁺) were measured by using argon and helium discharge gases. The SPI source was installed to a commercially used quadrupole mass analyzer for analyzing organic compounds. To demonstrate the SPI source, the mass spectra of some organic compounds (methylene chloride, toluene, benzene, cyclohexane and chloroform) were measured. The organic compounds were ionized with good stability in the plasma, and the fragmentation depended on the applied current. When helium and argon gases were used as the discharge gas, the helium plasma was more suitable for SPI-MS rather than argon because the argon plasma not only suffers from spectral interference but also has lower sensitivity.     

Measurement of volatile organic compounds in vehicle exhaust using single-photon ionization time-of-flight mass spectrometry

For the real-time measurements of volatile organic compounds (VOCs) in vehicle exhaust, we employed a vacuum ultraviolet single-photon ionization time-of-flight mass spectrometer (VUV-SPI-TOFMS). Exhaust measurements from gasoline and diesel engine vehicles were performed using a chassis dynamometer. Hydrocarbons such as alkylbenzenes, alkenes, alkanes, and dienes were the major organic compounds present in both gasoline and diesel engine exhaust. The concentrations of organic compounds in gasoline exhaust were higher under running conditions than during idling. The VOC concentrations in diesel exhaust were higher during idling than during running conditions. The VUV-SPI-TOFMS measured composition and emission profiles of many hydrocarbons, including aliphatics and aromatics, in vehicle exhaust simultaneously with real time response.