Gas-phase ion chemistry in the ternary silane-propyne-phosphine system

The gas-phase ion chemistry of propyne-phosphine and silane-propyne-phosphine mixtures was studied by ion trap mass spectrometry. For the binary mixture, the effect of different partial pressures of the reagents on the yield of C and P-containing ions was evaluated. Reaction sequences and rate constants were determined and reaction efficiencies were calculated from comparison of experimental and collisional rate constants. In the ternary silane-propyne-phosphine systems, the reaction pathways leading to formation of Si(m)C(n)P(p)H(q) (+) ions were determined and the rate constants of the most important steps were measured. For some ion species, selected by double isolation procedures (MS/MS), the low ion abundances prevented determination of the reaction rate constants. Si, C and P-containing ions are mainly produced in reactions of Si(m)P(p)H(q) (+) ions with propyne, while the reactivity of the Si(m)C(n)H(q) (+) ions towards PH(3) and of the C(n)P(p)H(q) (+) ions towards SiH(4) is very low. The formation of hydrogenated Si--C--P ions is interesting for their possible role as precursors of amorphous silicon carbides doped with phosphorus, obtained in a single step, by deposition from properly activated silane-propyne-phosphine mixtures.     

Gas-phase ion chemistry of the allene-phosphine and silane-allene-phosphine systems

The gas-phase ion chemistry of allene-phosphine and silane-allene-phosphine mixtures was studied by ion trap mass spectrometry. Rate constants of the main processes were measured and compared with the collisional rate constants to determine the reaction efficiencies. For the binary mixture, the highest yield of C- and P-containing ions is obtained with a 1 : 1 partial pressure ratio among the reagents. In the ternary mixture, formation of ion species containing Si, C and P together is mainly achieved in reactions of Si/P ions with allene, with a lower contribution from reactions of Si/C and C/P ions with phosphine and silane, respectively. The formation of ternary ion clusters is related to their possible role as precursors of amorphous silicon carbides doped with phosphorus, obtained by deposition from properly activated silane-allene-phosphine mixtures.     

Gas-phase ion chemistry in the ternary SiH4-C3H6-NH3 system

The gas-phase ion chemistry of propene-ammonia and silane-propene-ammonia mixtures was studied by ion trap mass spectrometry. As far as the binary mixture is concerned, the effect of different molar ratios of the reactants on the trend of ion species formed was evaluated, the ion-molecule reaction processes were identified and the rate constants for the main processes were measured. The results were compared with the collisional rate constants to determine the reaction efficiencies. In the ternary silane-propene-ammonia mixture the mechanisms of formation of Si(m)C(n)N(p)H(q)(+) clusters were elucidated and the rate constants of the most important steps were measured. For some species, selected by double isolation (MS/MS), the low abundance of the ions allowed us to determine the reaction paths but not the rate constants. Ternary ions are mainly formed by reactions of Si(m)C(n)H(q)(+) ions with ammonia, whereas a minor contribution comes from reactions of Si(m)N(p)H(q)(+) ions with propene. On the other hand, the C(n)N(p)H(q)(+) ions showed a very low reactivity and no step leading to ternary ion species was identified. The formation of hydrogenated ternary ions with Si, C and N has a basic importance in relation to their possible role as precursors of amorphous silicon carbides doped with nitrogen obtained by deposition from silane-propene-ammonia mixtures properly activated.     

Gas-phase ion chemistry in XH4--C3H4--ZH3 (X==Si, Ge; Z==N, P) mixtures

The gas-phase ion chemistry of silane-allene-ammonia, germane-allene (or propyne)-ammonia (or phosphine) systems was studied by ion trap mass spectrometry. Reaction sequences were determined and rate constants were measured for the main processes observed. The mixture containing silane displays higher reactivity with respect to that with germane. Comparison with analogous systems provides useful information about the reactivity of different hydrocarbon molecules and the different affinities of silicon and germanium towards nitrogen and phosphorus. The most interesting product ions observed are those containing Si (or Ge), C and N (or P) elements together, as these ion species may be considered precursors of doped amorphous carbides, which are widely used in semiconductor devices.     

Gas-phase ion chemistry in germane-propane and germane-propene mixtures

Germane-propane and germane-propene gaseous mixtures were studied by ion trap mass spectrometry. Variations of ion abundances observed under different partial pressure ratios and mechanisms of ion-molecule reactions elucidated by multiple isolation steps are reported. In addition, the rate constants for the main reactions were experimentally determined and compared with the collisional rate constants to obtain the reaction efficiencies. The yield of ions containing both Ge and C atoms is higher in the germane-propene than in the germane-propane system. In the former mixture, chain propagation takes place starting from germane ions reacting with propene and proceeds with the formation of clusters such as Ge(2)C(4)H(n) (+) and Ge(3)CH(n) (+).     

Ion/Molecule reactions in SiH4/H2S and GeH4/H2S mixtures

The gas phase ion chemistry of silane/hydrogen sulfide and germane/hydrogen sulfide mixtures was studied by ion trap mass spectrometry (ITMS), in both positive and negative ionization mode. In positive ionization, formation of X/S (X = Si, Ge) mixed ions mainly takes place via reactions of silane or germane ions with H₂S, through condensation followed by dehydrogenation. This is particularly evident in the system with silane. On the other side, reactions of H_nS₂⁺ ions with XH₄ (X = Si, Ge) invariably lead to formation of a single X? S bond. In negative ionization, a more limited number of mixed ion species is detected, but their overall abundance reaches appreciable values, especially in the SiH₄/H₂S system. Present results clearly indicate that ion processes play an important role in formation and growth of clusters eventually leading to deposition of amorphous solids in chemical vapor deposition (CVD) processes. Copyright © 2009 John Wiley & Sons, Ltd.     

Gas-phase chemistry of ionized and protonated GeF4: a joint experimental and theoretical study

The gas-phase ion chemistry of GeF(4) and of its mixtures with water, ammonia and hydrocarbons was investigated by ion trap mass spectrometry (ITMS) and ab initio calculations. Under ITMS conditions, the only fragment detected from ionized GeF(4) is GeF(3)(+). This cation is a strong Lewis acid, able to react with H(2)O, NH(3) and the unsaturated C(2)H(2), C(2)H(4) and C(6)H(6) by addition-HF elimination reactions to form F(2)Ge(XH)(+), FGe(XH)(2)(+), Ge(XH)(3)(+) (X = OH or NH(2)), F(2)GeC(2)H(+), F(2)GeC(2)H(3)(+) and F(2)GeC(6)H(5)(+). The structure, stability and thermochemistry of these products and the mechanistic aspects of the exemplary reactions of GeF(3)(+) with H(2)O, NH(3) and C(6)H(6) were investigated by MP2 and coupled cluster calculations. The experimental proton affinity (PA) and gas basicity (GB) of GeF(4) were estimated as 121.5 ± 6.0 and 117.1 ± 6.0 kcal mol(-1), respectively, and GeF(4)H(+) was theoretically characterized as an ion-dipole complex between GeF(3)(+) and HF. Consistently, it reacts with simple inorganic and organic molecules to form GeF(3)(+)-L complexes (L = H(2)O, NH(3), C(2)H(2), C(2)H(4), C(6)H(6), CO(2), SO(2) and GeF(4)). The theoretical investigation of the stability of these ions with respect to GeF(3)(+) and L disclosed nearly linear correlations between their dissociation enthalpies and free energies and the PA and GB of L. Comparing the behavior of GeF(3)(+) with the previously investigated CF(3)(+) and SiF(3)(+) revealed a periodically reversed order of reactivity CF(3)(+) < GeF(3)(+) < SiF(3)(+). This parallels the order of the Lewis acidities of the three cations.     

Gas-phase ion chemistry of GeH(4)/B(2)H(6) mixtures

The gas phase ion-molecule reactions in positively and negatively ionized germane/diborane mixtures have been studied by ion trap mass spectrometry. Reaction sequences and rate constants for the most interesting processes have been determined. In positive ionization, formation of Ge-B bonds exclusively occurs through condensation reactions of B(n)H(m)(+) ions with germane, followed by H(2) or BH(3) loss. No reactions of ions from germane with B(2)H(6) were observed under the experimental conditions used here. In negative ionization, the Ge(n)H(m)(-) (n = 1, 2) ion families react with diborane to yield the Ge(n)B(p)H(q)(-) (p = 1, 2) ions, again via dehydrogenation and BH(3) loss, while diborane anions proved to be unreactive. In both positive and negative ionization, Ge-B ions reach appreciable abundances. The present results afford fundamental information about the intrinsic reactivity of gas-phase ions and provide valuable indications about the first nucleation steps ultimately leading to amorphous Ge and B-doped semiconductor materials by chemical vapor deposition methods.     

Gas-phase reactivity of the O=P(OCH3)2 + phosphonium ion towards alpha,beta-unsaturated esters in a quadrupole ion trap

Ion-molecule reactions between the O=P(OCH3)2 + phosphonium ions and eight alpha,beta-unsaturated esters (methyl acrylate, ethyl acrylate, methyl crotonate, ethyl crotonate, methyl 3,3-dimethylacrylate, ethyl 3,3-dimethylacrylate, methyl methacrylate and ethyl methacrylate) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH3)2 + phosphonium ions, formed by electron ionization from neutral trimethyl phosphite, were found to react with alpha,beta-unsaturated esters to give an adduct [RR'C=CR'COOR', O=P(OCH3)2]+, which lose spontaneously a molecule of trimethyl phosphate (R'=CH3) or dimethyl ethyl phosphate (R'=C2H5). An ion corresponding to a protonated trialkyl phosphate is also observed when substituent R'=H. To confirm the experimental results, and to elucidate the mechanism for the formation of the ionic species, a theoretical study using the density functional theory (DFT) approach was carried out. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH3)2 + and methyl acrylate is described.     

Neutral and ion chemistry in a C2H4-SiH4 discharge

This paper reports on a mass spectrometric study of the neutral and ionic species in a low-pressure rf discharge sustained in a C₂H₄-SiH₄ mixture diluted in helium. It is shown that C₂H₄ is readily decomposed into C₂H ₂ ^* and C₂H₃. The formation of secondary products such as C₄H₂, C₄H₄, and C₄H₆ is observed and confirms the presence of C₂H₂ in the discharge. Methylsilane (CH₃SiH₃) and ethylsilane (C₂H₅SiH₃) are also synthesized in this discharge. It is also observed that the major ions C₂H ₄ ⁺ , C₃H ₅ ⁺ , SiH ₃ ⁺ , Si₂H ₄ ⁺ , SiCH ₃ ⁺ , SiC₂H ₃ ⁺ , and SiC₂H ₇ ⁺ are not representative of the direct ionization of neutral species. Their formation is thus interpreted on the basis of ion-molecule reactions.     

Gas-phase reactivity of the O=P(OCH3)2+ phosphonium ion with aliphatic esters in a quadrupole ion trap. Spontaneous elimination of ketenes

Ion-molecule reactions between the O=P(OCH(3))(2) (+) phosphonium ions and five aliphatic esters (methyl acetate, methyl propionate, methyl 2-methylpropionate, methyl butyrate and ethyl acetate) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH(3))(2) (+) phosphonium ions, formed by electron ionization from neutral trimethyl phosphite, were found to react with aliphatic esters to give an adduct ion [RR'CHCOOR", O=P(OCH(3))(2)](+), which loses spontaneously a molecule of ketene CH(2)=CO or substituted ketenes RR'C=CO. Isotope-labeled methyl acetate was used to elucidate fragmentation mechanisms. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH(3))(2) (+) and methyl acetate is described.     

Determination of organotins in water by micro liquid chromatography–electrospray/ion trap mass spectrometry

Due to the varying toxicity the species of organotins in their widespread applications, it is important for analytical methods to address their speciation. Traditional methods call for the hydrolysis and subsequent derivatization of the organotins before analysis. These methods can be time‐consuming, derivatization can be incomplete and high levels of background interference produce difficulties in identification and quantification. The use is described of a non‐derivatization and non‐hydrolysis micro‐liquid chromatography–electrospray/ion trap mass spectrometry for separation and detection of the organotins. Copyright © 1999 John Wiley & Sons, Ltd.     

Fragmentation studies on the antibiotic avilamycin A using ion trap mass spectrometry

A comprehensive study on the fragmentation pattern of the antimicrobial growth promoter avilamycin A was conducted in a quadrupole ion trap mass spectrometer equipped with an electrospray ionization (ESI) source. Performing multiple-stage experiments on the deprotonated molecule (m/z 1401) and its principal product ions showed that a sequential shortening of the oligosaccharide backbone took place, which can be attributed to the localization of the negative charge in the terminal dichloroisoeverninic acid. Under (+)-ESI conditions, avilamycin A readily formed an intense sodium-cationized molecule, [M + Na](+) (m/z 1425). Structural elucidation of the second-, third- and fourth-generation fragment ions revealed that all of the structures shared a common molecular portion comprising a central monosaccharide. This observation allowed us to assign confidently the complexation site of the alkali metal cation. In addition to the monosodiated molecule, the full-scan mass spectral acquisition also yielded a less abundant disodiated molecule, [M - H + 2Na](+) (m/z 1447). Multiple-stage experiments on this ion indicated that the second sodium ion compensates for the negative charge located at either of two positions within the molecule. While deprotonation of the phenolic hydroxyl group in the dichloroisoeverninic acid moiety was suggested to be driven by charge stabilization in the aromatic ring (in analogy with the deprotonated molecule in the (-)-ESI mode), the deprotonation at an alpha-carbon of an ester side-chain substituent in the oligosaccharide part was believed to provide a stable chelation-like coordination site for the cation.     

Analysis of rare-earth elements in soil sample by using laser-ablation ion trap mass spectrometry

Laser-ablation ion trap mass spectrometry (LA-ITMS) is applied for the analysis of rare-earth elements in soil samples. The target elements studied in this work were ytterbium (Yb) and samarium (Sm). The isotopic compositions of these elements were analyzed for standard samples with chip shape, the western phosphate rock sample (NIST SRM-694), and soil samples collected near our laboratory. For metal samples of Sm and Yb, isotopes of these elements as well as oxide forms were clearly identified. For the case of soil samples only a tentative assignment on the mass peaks were performed due to the complicated mass spectra that originated from the oxide forms of various rare-earth elements.     

Analysis of trifluoroacetic acid and other short-chain perfluorinated acids (C2-C4) in precipitation by liquid chromatography-tandem mass spectrometry: comparison to patterns of long-chain perfluorinated acids (C5-C18)

This paper provides analytical chemical information on selected new molecular entities (NMEs) which are drugs that have recently been approved by the FDA. These are the antiretroviral drugs, atazanavir, indinavir and emtricitabine, the antibacterial gemifloxacin, rosuvastatine which is a cholesterol-lowing drug, the anti-cancer drug gefitinib and aprepitant for neurological disorders. Electrospray ionisation-quadrupole ion trap mass spectrometry (ESI-MSⁿ) was employed to generate tandem mass spectrometric (MS²) data of the drugs studied and structural assignments of product ions were supported by quadrupole time-of-flight mass spectrometry (QToF-MS/MS). These fragmentation studies were then utilised in the development and validation of a specific and sensitive liquid chromatographic method (LC–ESI-MS²) to identify and determine these drugs at therapeutic concentration levels in serum after a single protein precipitation procedure with acetonitrile. In addition, this method was compared to the application of gas liquid chromatography-flame ionisation detection (GLC-FID) and differential pulse polarography (DPP) for the analysis of these NMEs in serum.     

Extensive study on physicochemical properties of polychlorinated biphenyls in a commercial ion trap mass spectrometer,relevance in analytical and environmental chemistry

Polychlorinated biphenyls (PCBs) exist as 209 congeners, consisting of biphenyl molecules, where the number and substitution positions of halogen atoms are known to affect industrial uses, environmental transport mechanisms, distribution, fate, and toxicity. The complexity of the problem requires accurate physicochemical studies of an increasing number of congeners in order to understand the environmental and biological processes at play. This work presents a systematic study on the thermodynamic and kinetic properties of PCBs by quadrupole ion trap mass spectrometry. A clear relationship between structure and behavior of PCBs in mass spectrometry experiments has been observed. Overall data demonstrate that di‐ortho congeners show lower thermodynamic stability and higher fragmentation rate than non/mono‐ortho. Congeners follow different fragmentation mechanisms according to the number of chlorine atoms in ortho position of the biphenyl system. Experimental kinetic curves of mono/non‐ortho and di‐ortho congeners show a strong similarity with classical first‐order kinetics curves; in particular, di‐ortho congeners follow a first‐order consecutive reaction, while mono/non‐ortho follow a first‐order parallel reaction. For each studied congener, the kinetic constant of reaction (fragmentation) has been determined. Data support environmental levels and biochemical transformations described in literature. The general picture of the PCB behavior inside a quadrupole ion trap provides the basis for the development of reliable and cost‐effective analytical methods to the determination of ultra‐low level trace of PCB congeners.     

Influence of a ring substituent on the tendency to form H(2)O adducts to Ag(+) complexes with phenylalanine analogues in an ion trap mass spectrometer

In a previous report we showed that certain binary Ag(+)-amino acid complexes formed adduct ions by the attachment of a single water and methanol molecule when stored in an ion trap mass spectrometer: complexes with aliphatic amino acids and with 4-fluorophenylalanine formed the adduct ions whereas complexes with phenylalanine and tryptophan did not. In this study we compared the tendency of the Ag(+) complexes derived from phenylalanine, 4-fluorophenylalanine, 4-hydroxyphenylalanine (tyrosine), 4-bromophenylalanine, 4-nitrophenylalanine and aminocyclohexanepropionic acid to form water adducts when stored, without further activation, in the ion trap for times ranging from 1 to 500 ms. Because the donation of pi electron density to the Ag(+) ion is a likely determining factor in complex reactivity, our aim in the present study was to determine qualitatively the influence of para-position substituents on the aromatic ring on the formation of the water adducts. Our results show that the reactivity of the complexes is influenced significantly by the presence of the various substituents. Decreases in [M + Ag](+) ion abundance, and increases in adduct ion abundance, both measured as a function of storage time, follow the trend -NO(2) > -Br > -F > -OH > -H. The complex of Ag(+) with 4-nitrophenylalanine was nearly as reactive towards water as the Ag(+) complex with aminocyclohexanepropionic acid, the last being an amino acid devoid of pi character in the ring system. Collision induced dissociation of the [M + Ag](+) species derived from the amino acids produces, among other products, Ag(+) complexes with a para-substituted phenylacetaldehyde: complexes that also form adduct species when stored in the ion trap. The trends in adduct ion formation exhibited by the aldehyde-Ag(+) complex ions were similar to those observed for the precursor complexes of Ag(+) and the amino acids, confirming the influence of the ring substituent.     

稳定图的测定与矩形离子阱质谱性能分析

从理论上讲, 离子阱质谱仪的性能是由阱内电场分布决定的,而电场分布又是由组成离子阱的电极几何结构和离子阱工作电压决定的. 对于矩形离子阱, 即使不考虑其几何结构的偏差, 其阱内的电场分布一般也很复杂. 在矩形离子阱内, 除四极电场外, 还包含多种成分的其他各种高阶场, 它们直接影响离子在阱内的运动轨迹和离子阱质谱的性能. 由于各种电场成分对离子阱内离子运动的影响非常复杂, 还很难从数学上给出精确的解析解, 使得目前从理论上还无法预测高阶场成分对质谱性能的影响. 本工作通过测定不同几何结构的矩形离子阱的稳定图, 从实验上比较了不同场半径, 即不同电场分布条件下的离子阱质谱性能的差别. 实验中, 通过改变离子阱的几何比例结构, 详细测定了不同结构的矩形离子阱的稳定图特征, 并与实验测得的质谱分析结果进行比较. 同时, 我们还详细介绍了矩形离子阱质谱的稳定图的测定方法, 并根据得到的不同情况下的稳定图结构分析了离子阱的质谱性能. 研究结果表明： 可以通过比较试验得到的稳定图结构来判断其离子阱质谱仪的性能如质量分辨能力等. 此外, 实验结果还发现： 对于y方向拉伸结构的矩形离子阱, 其实验绘制得到的是不完整的稳定图. 但根据稳定图边界的特点, 通过采用四极直流电压调制的方法, 可以对y方向拉伸结构的矩形离子阱的性能进行改善, 极大地提高了阱的质量分辨能力.