Telluroxide elimination by direct oxidation of alkyl phenyl telluride

Treatment of sec-alkyl phenyl tellurides, except for the cyclohexyl system, with m-chloroperbenzoic acid(MCPBA) in diethyl ether readily afforded the corresponding olefins in good yields presumably via telluroxide elimination together with small amounts of alcohols and ketones. In the pri-alkyl and cyclohexyl cases the adducts between MCPBA and the tellurides were isolated as stable organotellurium(IV) compounds which gave similar elimination products by neat pyrolysis at 220–2500°C.     

Gas chromatography and mass spectrometry of methoxylated polybrominated diphenyl ethers (MeO-PBDEs)

Twenty-six methoxylated polybrominated diphenyl ethers (MeO-PBDEs) were characterized by gas chromatography (GC) on four different GC columns with different lengths and polarities, as well as by mass spectrometry using three ionization techniques, electron ionization (EI), electron capture negative ionization (ECNI) and positive ion chemical ionization (PICI). MeO-PBDE congeners with similar retention times on a nonpolar GC column were separated when analyzed on a polar GC column. EI can be used to determine the position of the methoxy substituent (ortho, meta or para) relative to the diphenyl ether oxygen in the MeO-PBDEs. The PICI ionization technique is shown to be valuable to generate structural information of the MeO-PBDEs, i.e. the degree of bromination on both the methoxy-substituted ring and the entirely brominated phenyl ring can be obtained. This structure information can also be achieved for certain MeO-PBDEs with the methoxy group in ortho position to the diphenyl ether bond in ECNI mode. Like other brominated compounds ECNI is preferable when analyzing environmental samples for quantification of MeO-PBDEs because of the formation of bromide ions, which enables low detection limits.     

食品中多溴联苯醚残留的气相色谱-串联质谱分析方法研究

建立了食品中8种多溴联苯醚(PBDEs) 残留的气相色谱-串联质谱分析方法,初步解析了PBDEs的电子轰击串联质谱(EI MS/MS)图,为各种目标物的准确定性分析提供依据.以BDE-28、BDE-47、BDE-66、BDE-85、BDE-99、BDE-100、BDE-153、BDE-154为研究对象,对EI MS/MS各分析参数进行了优化.用超声提取-酸性硅胶层析柱净化的前处理方法制备样品,当空白样品的加标水平为10.0、25.0 μg/kg时,8种PBDEs的平均加标回收率为82% ～112%,相对标准偏差为3.1% ～15%,方法检出限均低于1.5 μg/kg;8种PBDEs的线性范围为10.0 ～500 μg/kg,相关系数均大于0.994 7.     

多溴联苯醚代谢物的色谱保留和质谱特征

研究了多溴联苯醚(PBDEs)代谢物中常见的18种羟基PBDEs(HO-BDEs)、15种甲氧基PBDEs(MeO-BDEs)的气相色谱、反相液相色谱分离和质谱碎片特征。MeO-BDEs在反相液相色谱(RPLC)的保留行为受疏水作用支配,而HO-BDEs则还受到除疏水作用以外的特殊作用影响。LC/MS中大气压化学电离(APCI)源适用于HO-BDEs检测,而APCI源以及电喷雾离子源(ESI)对MeO-BDEs都没有响应。质谱碎片具有显著取代位效应:在LC/APCI-MS中,邻位取代HO-BDEs的碎片离子基峰均为脱一个溴的结构[M-H]--HBr,而对位取代的基峰则为准分子离子[M-H]-;在电子电离(EI)源质谱仪下,邻位取代MeO-BDEs有脱溴甲烷碎片离子(M. -BrCH3),对位取代有特征的脱甲基自由基结构(M. -.CH3),间位取代则无上述两种碎片离子。     

有机硒和碲化学的新进展

本文着重对最近几年来有机硒和碲化合物在有机合成中的应用进行了简要的综述。现在就硒和碲化合物作为反应试剂、在有机分子中引入硒和碲的方法以及从有机分中除去硒和碲的方法三个方面进行了讨论。由此也可见,有机硒和缔化合物在有机合成中的重要性。     

Potential chlorinated and brominated interferences on the polybrominated diphenyl ether determinations by gas chromatography-mass spectrometry

The analysis of polybrominated diphenyl ether (PBDE) congeners by GC-MS was studied in terms of potential interferences. Different MS approaches were normally used for the PBDE analyses: negative ion chemical ionization (NICI-MS) and electron ionization (EI-MS). This paper studied the presence of potential interferences in each instrumental technique approach, principally those corresponding to different chlorinated compounds (PCBs, PCNs, etc.) as well as brominated compounds (PBBs, MeO-PBDEs, TBBPA, etc.). The two ionization modes are subjected to different types of interferences. In general, EI-MS is affected by chlorinated interferences, especially PCBs. NICI-MS eliminated chlorinated interferences but presented different brominated interferences, well resolved with the EI-MS approach.     

Atmospheric pressure photoionization mechanisms. 2. The case of benzene and toluene

Benzene and toluene have been proposed previously as dopants in atmospheric pressure photoionization (APPI) experiments on compounds exhibiting ionization energies higher than the energy of photons used for irradiation. Their low ionization energies lead to their easy photoionization and the ions so formed lead to the ionization of analytes through charge exchange. However, some measurements have shown that some protonation reactions also take place, and a series of experiments was undertaken to investigate this unexpected behavior. It was shown that, when benzene is irradiated in the APPI source, the odd-electron molecular ions of phenol, diphenyl ether and phenoxyphenol are produced in high yield, together with protonated diphenyl ether and protonated phenoxyphenol. These results have been confirmed by deuterium labelling and MS(n) experiments. A possible mechanism is proposed, based on a radical attack by benzene molecular ions on oxygen molecules present inside the APPI source, analogous to that proposed in the literature for phenyl radicals. Similar results have been obtained with toluene, proving that APPI is able to activate a series of reactions leading to highly reactive species which are highly effective in promoting ionization of molecules with ionization energies higher than the photon energy.     

Stereochemical applications of mass spectrometry. II—Chemical ionization mass spectra of isomeric dicarboxylic acids and derivatives

The H₂ and CH₄, chemical ionization mass spectra of the cis dicarboxylic acids, maleic and citraconic acid, show much more extensive loss of H₂O from [MH]⁺ than the trans isomers, fumaric acid and mesaconic acid. Similarly, esters of maleic acid show a much more facile loss of ROH (R=alkyl or phenyl) from [MH]⁺ than do esters of fumaric acid. Similar differences are observed in the chemical ionization mass spectra of the isomeric phthalic and isophthalic acids and derivatives, where the ortho isomers show more extensive fragmentation of [MH]⁺ than the meta isomers. The facile fragmentation of [MH]⁺ for the cis and ortho isomers is attributed to ROH elimination involving interaction between the two carboxylate functions and forming the stable cyclic anhydride structure for the fragment ion. By contrast ROH elimination from [MH]⁺ for the trans and metu isomers requires a symmetry-forbidden [1,3]-H migration in the carboxyl protonated species and cannot lead to the cyclic anhydride structure. The chemical ionization mass spectra of cis and trans cyclohexane-1,2-dicarboxylic acids are essentially identical and show extensive fragmentation of the [IMH]⁺ ion. Experiments using deuterium labelling show extensive carboxyl group interactions for both isomers. The chemical ionization mass spectra of maleanilic and phthalanilic acids and of the related anhydrides and imides also are reported, as are the electron impact mass spectra of diphenyl maleate, diphenyl fumarate, diphenyl phthalate, maleanilic acid and phthalanilic acid.     

Determination of PBDEs in human breast adipose tissues by gas chromatography coupled with triple quadrupole mass spectrometry

The potential of gas chromatography/tandem mass spectrometry with a triple quadrupole analyzer for determination of 12 polybrominated diphenyl ethers in human breast tissues has been investigated. After extraction with hexane, two purification procedures-automated normal-phase high-performance liquid chromatography and solid-phase extraction-were assayed. Both electron impact ionization, in selected reaction monitoring mode, and negative chemical ionization, in selected ion recording mode, were tested for the optimum determination of analytes. Isotopically labeled standards were added before extraction as surrogates: [¹³C]BDE47, [¹³C]BDE99 and [¹³C]BDE153 for electron impact ionization, and p,p′-DDE-d ₈ for negative chemical ionization. The method was validated in terms of accuracy, precision, limits of detection and limits of quantification, using human breast tissue spiked at three levels in the range 1–50 ng/g (5–250 ng/g for BDE209). The analytical approach using solid-phase extraction cleanup followed by gas chromatography/mass spectrometry (negative chemical ionization ) led to lower detection limits (0.006–2 ng/g) and allowed the determination of the most problematic congener, BDE209, whose poor sensitivity made difficult its determination at low residue levels. Special attention was given to the confirmation of the compounds detected in samples in order to avoid reporting false positives. Two tandem mass spectrometry transitions or three m/z ions were selected for each analyte when using electron impact ionization or negative chemical ionization modes, respectively. In both cases, the transition to ion intensity ratio was used as a confirmation parameter. The method developed was applied to the analysis of real human samples. Several brominated diphenyl ethers (congeners 47, 100, 99, 154, 153, 183 and 209) were detected in the range 0.08–0.23 ng/g.     

Mass spectrometric characteristics of decabromodiphenyl ether and the application of isotopic dilution in the electron capture negative ionization mode for the analysis of polybrominated diphenyl ethers

The mass spectrometric properties of (12)C-and (13)C-labeled decabromodiphenyl ether (BDE-209) in the low-resolution mass spectrometry electron capture negative ionization mode (ECNI-MS) is described in detail and are compared with those of polybrominated diphenyl ethers (PBDEs) with a lower degree of bromination. The mass spectrometric properties of BDE-209 make it possible to apply (13)C-labeled BDE-209 as an internal surrogate standard for the determination of BDE-209 by isotopic dilution. A combination of the [Br](-) and [C(6)Br(5)O](-) fragment ions is proposed for the detection with ECNI-MS in the selected ion monitoring mode to increase selectivity, sensitivity and accuracy in the determination of decabromodiphenyl ether together with other polybrominated diphenyl ethers. The importance of optimizing the instrument parameters to obtain optimal response from the mass spectrometer in the analysis of PBDEs is discussed in detail.     

Wavelength-dependent fragmentation in resonance-enhanced multiphoton ionization mass spectrometry

Wavelength-dependent effects in the resonance-enhanced multiphoton ionization/fragmentation mass spectra of p-chloroaniline and diphenyl ether are presented. For both molecules, the formation of low-energy fragments can be discriminated against in favor of higher-energy fragments by using ‘low’-energy radiation (290 nm region) for ionization/fragmentation. The same low-energy fragments become dominant when higher-energy radiation (266 nm) is used. This unique behavior is explained in terms of the narrow distribution of parent ion internal energies created through resonance-enhanced multiphoton ionization/fragmentation and the competing kinetic processes accessed by the parent ion as it absorbs each successive photon.     

125Te-NMR-spektren von organotellurhalogeniden

Tetraorganotin compounds react with tellurium tetrachloride or tellurium tetrabromide with formation of the corresponding organotellurium trihalides and diorganotellurium dihalides. ¹²⁵Te NMR spectra of the reaction mixtures are used to determine the reaction products.     

有机磷化合物的质谱研究(Ⅺ)——1,3,2—二氮磷杂环戊烷衍生物的化学电离质谱

本文报道了11种1,3,2-二氮磷杂环戊烷衍生物的化学电离质谱(CIMS),对热不稳定的化合物采用了解吸化学电离技术(DCI),着重探讨了三价磷和五价磷化合物质谱的差异及均三氮苯取代基的引入对质谱行为的影响;对该类化合物的CIMS和EIMS进行了比较。     

新型溴代羟基二苯醚的合成及抑菌活性研究

设计并合成了10个新的溴代羟基二苯醚, 所有这些化合物的结构均经过¹H NMR, MS, IR和元素分析所证实. 新化合物的结构避免了现有卤代2-羟基二苯醚杀菌剂在生产和使用过程中有可能生成高毒性二噁英类化合物的缺点. 选择几种有害菌对合成的溴代羟基二苯醚进行了抑菌活性检测, 证实它们对所测试菌种具有优良的抑制效果.     

Investigation of combwax of honeybees with high-temperature gas chromatography and high-temperature gas chromatography-chemical ionization mass spectrometry. II: High-temperature gas chromatography-chemical ionization mass spectrometry

Crude combwax of six various honey bee species have been analyzed by high-temperature gas chromatography (HTGC)-chemical ionization mass spectrometry after a two-step silylation procedure. An optimized chromatographic procedure, described previously, enables the separation of high-molecular mass lipid compounds resulting in a characteristic fingerprint of the combwaxes of different honeybee species. The coupling of HTGC to mass spectrometry requires appropriate instrumentation in order to achieve sufficient sensitivity at high elution temperatures and avoid loss of chromatographic resolution. Chemical ionization was carried out using methane as reagent gas in order to determine the molecular mass of the individual compounds by means of abundant quasi molecular ions. To confirm the presence of unsaturated wax esters, ammonia was used as reagent gas. More than 80 lipid constituents were separated and characterized by their mass spectra. Representative chemical ionization mass spectra of individual compounds are presented. Both, HTGC-flame ionization detection data and the results of the HTGC-mass spectrometric investigations enabled a rapid profiling of the individual classes of compounds in crude combwaxes.     

Synthetic and theoretical studies on group-transfer imidoylation of organotellurium compounds. remarkable reactivity of isonitriles in comparison with carbon monoxide in radical-mediated reactions.

Imidoylation of organotellurium compounds with isonitriles has been investigated in conjunction with the radical-mediated C1 homologation reaction by using CO and isonitriles. Carbon-centered radicals generated photochemically or thermally from organotellurium compounds react with isonitriles in a group-transfer manner to give the corresponding imidoylated products. Organotellurium compounds have been found to serve as effective precursors of a wide variety of stabilized radicals, namely benzyl, alpha-alkoxy, alpha-amino, and acyl radicals, which take part in the imidoylation with high efficiency. The reactions are compatible with various functional groups, and can be carried out in various solvents including environmentally benign water. The reactivity of isonitriles has been compared with that of CO through competition experiments, and the results indicate that isonitriles are superior to CO as radical acceptors in reactions with stabilized radicals. The origin of the differences has been addressed in theoretical studies with density functional theory calculations using the B3LYP hybrid functional. The calculations suggest that both carbonylation and imidoylation proceed with low activation energies, and that there are virtually no differences in the kinetic sense. Instead, it indicates that thermodynamic effects, namely differences in the stability of the acyl and the imidoyl radicals, control the overall course of the reactions.     

Investigation of reagent gases for the positive chemical ionization of select polybrominated diphenyl ethers

Polybrominated diphenyl ethers (PBDEs) fall into the class of compounds known as brominated flame retardants and their incorporation in a multitude of products is responsible for saving numerous lives. However, toxicology studies have alerted researchers to the potential adverse health effects that may develop as a result of prolonged or extreme exposure to these compounds. Frequent disposal and subsequent leaching has focused concern on environmental concentrations and current reports cite increasing levels. Method development continues in support of this research and the present work examines the feasibility of utilizing gas chromatography ion trap mass spectrometry operating in positive ion chemical ionization mode. In the evaluation of reagents for chemical ionization (methane, methanol and acetonitrile), comparative results of all three reagents demonstrated more difficult protonation as the number of bromine atoms increased. Methane, possessing the lowest proton affinity, provided the highest response for the analytes. Further, when methane chemical ionization was compared to electron impact ionization, the tetra-congener showed approximately 8× greater sensitivity and the penta- and hexa-congeners demonstrated approximately 2× greater. CI parameters, such as ionization and reaction times, were optimized to provide the highest analyte response and this was followed by the investigation of the employment of MSⁿ. In the this mode, optimal excitation amplitude delivered sufficient fragmentation while maintaining maximum signal, yielding final instrument detection limits in the sub µg L^{− 1} range.     

Sites of protonation in phenothiazines: Methane and ammonia chemical ionization mass spectra

Positive ion methane and ammonia chemical ionization mass spectra for ten phenothiazine derivatives are reported. The fragmentations observed in the chemical ionization mass spectra are rationalized in terms of the location of the added proton. High-resolution measurements are used to confirm empirical formulae of the ions in the mass spectra. Changes in the mass spectra with a change in the chemical ionization reagent gas from methane to ammonia are described. A comparison with positive ion secondary ion mass spectra of the same compounds show that the amount of fragmentation is higher in the secondary ion mass spectra, but the same types of ions are observed in spectra produced by both ionization methods.     

α-Elimination of organic halides from organotellurium(IV) halides

Three types of α-elimination (oxidative, photolytic, and thermal) of organotellurium(IV) halides to give organic halides have been disclosed. Treatment of organotellurium(IV) halides with some oxidants, preferably t-butyl hydroperoxide, in 1,4-dioxane, acetic acid, or acetonitrile affords the corresponding organic halides in good yields with retention of configuration and by ipso-replacement. The reactivity order of this α-elimination is roughly as follows: alkyl > aryl > alkenyl. The main reaction course seems to be a 1,2-tellurium halogen shift in unstable organotellurium(VI) compounds formed in situ by oxidation. Similar α-elimination also occurs by photolysis of these compounds with a high-pressure mercury lamp in benzene as the solvent. Here, a cross-coupling of the organic moiety with benzene scarcely occurs except for the cases of diaryltellurium(IV) dihalides. Neat pyrolysis of some alkyl(phenyl)tellurium(IV) dibromides at 200–250 °C (Kugelrohr distillation apparatus) again results in α-elimination to produce the corresponding alkyl bromides almost quantitatively.     

Organic ion imaging of biological tissue with secondary ion mass spectrometry and matrix-assisted laser desorption/ionization

Organic secondary ion mass spectrometry (SIMS) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry can be used to produce molecular images of samples. This is achieved through ionization from a clearly identified point on a flat sample, and performing a raster of the sample by moving the point of ionization over the sample surface. The unique analytical capabilities of mass spectrometry for mapping a variety of biological samples at the tissue level are discussed. SIMS provides information on the spatial distribution of the elements and low molecular mass compounds as well as molecular structures on these compounds, while MALDI yields spatial information about higher molecular mass compounds, including their distributions in tissues at very low levels, as well as information on the molecular structures of these compounds. Application of these methods to analytical problems requires appropriate instrumentation, sample preparation methodology, and a data presentation usually in a three-coordinate plot where x and y are physical dimensions of the sample and z is the signal amplitude. The use of imaging mass spectrometry is illustrated with several biological systems.