Determination of relative sensitivity factors during secondary ion sputtering of silicate glasses by Au+, Au and Au ions

In recent years, Au‐cluster ions have been successfully used for organic analysis in secondary ion mass spectrometry. Cluster ions, such as Au and Au, can produce secondary ion yield enhancements of up to a factor of 300 for high mass organic molecules with minimal sample damage. In this study, the potential for using Au⁺, Au and Au primary ions for the analysis of inorganic samples is investigated by analyzing a range of silicate glass standards. Practical secondary ion yields for both Au and Au ions are enhanced relative to those for Au⁺, consistent with their increased sputter rates. No elevation in ionization efficiency was found for the cluster primary ions. Relative sensitivity factors for major and trace elements in the standards showed no improvement in quantification with Au and Au ions over the use of Au⁺ ions. Higher achievable primary ion currents for Au⁺ ions than for Au and Au allow for more precise analyses of elemental abundances within inorganic samples, making them the preferred choice, in contrast to the choice of Au and Au for the analysis of organic samples. The use of delayed secondary ion extraction can also boost secondary ion signals, although there is a loss of overall sensitivity. Copyright © 2009 John Wiley & Sons, Ltd.     

Experimental and theoretical investigation on binary anionic clusters of AlmBi

Al_mBi (m = 1–12; n = 1–4) binary cluster anions are generated by laser ablation of a sample composed of Al and Bi, and studied by reflectron time‐of‐flight mass spectrometry (RTOF‐MS) in the gas phase. Some clusters with magic numbers are present in the mass spectrum. The structures of Al_mBi (m + n ≤7) clusters are investigated with the density functional theory (DFT) method and the most likely structures are obtained. The calculations of the binding energy (BE), energy gain (Δ) and HOMO‐LUMO gaps confirm that the Al₂Bi cluster has a very stable structure, which agrees well with the experimental results. It is further established that Al₂Bi can be considered as a gas‐phase Zintl analogue that follows Wade's rules and is the analogue of Ga₂Bi and Sn Zintl ions. Copyright © 2009 John Wiley & Sons, Ltd.     

A fragmentation study of dihydroquercetin using triple quadrupole mass spectrometry and its application for identification of dihydroflavonols in Citrus juices

A mass spectrometric method using electrospray ionization with triple quadrupole and quadrupole time‐of‐flight hybrid (Q‐Tof) mass spectrometry has been applied to the structural characterization of dihydroflavonols. This family of compounds has been studied by liquid chromatography/tandem mass spectrometry (LC/MS/MS) for the first time in this work. A comprehensive study of the product ion MS spectra of the [M+H]⁺ ion of a commercially available standard has been performed. The most useful fragmentations in terms of structural identification are those that involve cleavage of the C‐ring, resulting in diagnostic ions of dihydroflavonol family: ^1,3A, ^1,2B, ^1,2B‐CO, ^0,2A, ^0,2A‐H₂O, ^0,2A‐CO, and ^0,2A‐H₂O‐CO, that allow the characterization of the substituents in the A‐ and B‐rings. In addition to those ions, other product ions due to losses of H₂O and CO molecules from the Y ion were observed. Their fragmentation mechanisms and ion structures have been proposed. The established fragmentation patterns have been used to successfully identity three dihydroflavonols found in tangerine juices for the first time. Copyright © 2009 John Wiley & Sons, Ltd.     

δ15N of soil N and plants in a N‐saturated,subtropical forest of southern China

We investigated the δ¹⁵N profile of N (extractable NH, NO, and organic N (EON)) in the soil of a N‐saturated subtropical forest. The order of δ¹⁵N in the soil was EON > NH > NO. Although the δ¹⁵N of EON had been expected to be similar to that of bulk soil N, it was higher than that of bulk soil N by 5‰. The difference in δ¹⁵N between bulk soil N and EON (Δ¹⁵N_bulk‐EON) was correlated significantly with the soil C/N ratio. This correlation implies that carbon availability, which determines the balance between N assimilation and dissimilation of soil microbes, is responsible for the high δ¹⁵N of EON, as in the case of soil microbial biomass δ¹⁵N. A thorough δ¹⁵N survey of available N (NH, NO, and EON) in the soil profiles from the organic layer to 100 cm depth revealed that the δ¹⁵N of the available N forms did not fully overlap with the δ¹⁵N of plants. This mismatch in δ¹⁵N between that of available N and that of plants reflects apparent isotopic fractionation during N uptake by plants, emphasizing the high N availability in this N‐saturated forest. Copyright © 2010 John Wiley & Sons, Ltd.     

Laser ablation of ternary As‐S‐Se glasses and time‐of‐flight mass spectrometric study

Ternary chalcogenide As‐S‐Se glasses, important for optics, computers, material science and technological applications, are often made by pulsed laser deposition (PLD) technology but the plasma composition formed during the process is mostly unknown. Therefore, the formation of clusters in a plasma plume from different glasses was followed by laser desorption ionization (LDI) or laser ablation (LA) time‐of‐flight mass spectrometry (TOF MS) in positive and negative ion modes. The LA of glasses of different composition leads to the formation of a number of binary As_pS_q, As_pSe_r and ternary As_pS_qSe_r singly charged clusters. Series of clusters with the ratio As:chalcogen = 3:3 (As₃S, As₃S₂Se⁺, As₃SSe), 3:4 (As₃S, As₃S₃Se⁺, As₃S₂Se, As₃SSe, As₃Se), 3:1 (As₃S⁺, As₃Se⁺), and 3:2 (As₃S, As₃SSe⁺, As₃Se), formed from both bulk and PLD‐deposited nano‐layer glass, were detected. The stoichiometry of the As_pS_qSe_r clusters was determined via isotopic envelope analysis and computer modeling. The structure of the clusters is discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Error assessment of nitrogen and oxygen isotope ratios of nitrate as determined via the bacterial denitrification method

Currently, bacterial denitrification is becoming the accepted method for δ¹⁵N‐ and δ¹⁸O‐NO determination. However, proper correction methods with international references (USGS32, USGS34 and USGS35) are needed. As a consequence, it is important to realize that the corrected isotope values are derived from a combination of several other measurements with associated uncertainties. Therefore, it is necessary to consider the propagated uncertainty on the final isotope value. This study demonstrates how to correctly estimate the uncertainty on corrected δ¹⁵N‐ and δ¹⁸O‐NO values using a first‐order Taylor series approximation. The bacterial denitrification method errors from 33 batches of 561 surface water samples varied from 0.2 to 2.1‰ for δ¹⁵N‐NO and from 0.7 to 2.3‰ for δ¹⁸O‐NO, which is slightly wider than the machine error, which varied from 0.2 to 0.6‰ for δ¹⁵N‐N₂O and from 0.4 to 1.0‰ for δ¹⁸O‐N₂O. The overall uncertainties, which are composed of the machine error and the method error, for the 33 batches ranged from 0.3 to 2.2‰ for δ¹⁵N‐NO and from 0.8 to 2.5‰ for δ¹⁸O‐NO. In addition, the mean corrected δ¹⁵N and δ¹⁸O values of 132 KNO₃‐IWS (internal working standard) measurements were computed as 8.4 ± 1.0‰ and 25.1 ± 2.0‰, which is a slight underestimation for δ¹⁵N and overestimation for δ¹⁸O compared with the accepted values (δ¹⁵N = 9.9 ± 0.3‰ and δ¹⁸O = 24.0 ± 0.3‰). The overall uncertainty of the bacterial denitrification method allows the use of this method for source identification of NO. Copyright © 2010 John Wiley & Sons, Ltd.     

Laser desorption ionization time‐of‐flight mass spectrometric study of binary As‐Se glasses

Binary chalcogenide As‐Se glasses and their thin films are important for optics, computers, materials science and technological applications. To increase understanding of the properties of thin films fabricated by plasma deposition techniques, more information concerning the physics of plasma plume is needed. In this study the formation of clusters in plasma plume from different As‐Se glasses by laser desorption ionization (LDI) or laser ablation (LA) was studied by time‐of‐flight mass spectrometry (TOF MS) in positive and negative ion modes. Formation of a number of As_pSe_q singly charged clusters As₃Se (q = 1–5), AsSe (q = 1–3), As₂Se (q = 2–4), and As₃Se (q = 2–5) was found from As‐Se glasses with the molar ratio As:Se in the range from 1:2 to 7:3. The stoichiometry of the As_pSe_q clusters was determined via isotopic envelope analysis and computer modeling. The structure of the clusters is proposed and the relationship to the structure of the parent glasses, as also suggested by Raman scattering spectra, is discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Contribution of atmospheric nitrate to stream‐water nitrate in Japanese coniferous forests revealed by the oxygen isotope ratio of nitrate

Evaluation of the openness of the nitrogen (N) cycle in forest ecosystems is important in efforts to improve forest management because the N supply often limits primary production. The use of the oxygen isotope ratio (δ¹⁸O) of nitrate is a promising approach to determine how effectively atmospheric nitrate can be retained in a forest ecosystem. We investigated the δ¹⁸O of nitrate in stream water in order to estimate the contribution of atmospheric NO in stream‐water NO (f_atm) from 26 watersheds with different stand ages (1–87 years) in Japan. The stream‐water nitrate concentrations were high in young forests whereas, in contrast, old forests discharged low‐nitrate stream water. These results implied a low f_atm and a closed N cycle in older forests. However, the δ¹⁸O values of nitrate in stream water revealed that f_atm values were higher in older forests than in younger forests. These results indicated that even in old forests, where the discharged N loss was small, atmospheric nitrate was not retained effectively. The steep slopes of the studied watersheds (>40°) which hinder the capturing of atmospheric nitrate by plants and microbes might be responsible for the inefficient utilization of atmospheric nitrate. Moreover, the unprocessed fraction of atmospheric nitrate in the stream‐water nitrate in the forest (f_unprocessed) was high in the young forest (78%), although f_unprocessed was stable and low for other forests (5–13%). This high f_unprocessed of the young forest indicated that the young forest retained neither atmospheric NO nor soil NO effectively, engendering high stream‐water NO concentrations. Copyright © 2010 John Wiley & Sons, Ltd.     

The reactions of a series of terpenoids with H(3) O(+) , NO(+) and O 2+ studied using selected ion flow tube mass spectrometry

The reactions of H₃O⁺, NO⁺ and O with twelve terpenoids and one terpene, all of which occur naturally in plants and which possess important smell and flavourant properties, were characterized using Selected Ion Flow Tube Mass Spectrometry (SIFT‐MS). The H₃O⁺ reactions resulted primarily in the formation of the proton transfer product and occasionally in a water elimination product. The NO⁺ reactions instead generated the charge transfer product or NO⁺ adducts, and occasionally alkyl fragments, or resulted in hydride abstraction. Reaction with O caused a higher fragmentation of the terpenoids with the molecular ion being the minor product of most reactions. Identification and quantification of each compound in complex mixtures are probably possible in most cases using the H₃O⁺ and/or NO⁺ precursors while O may be useful for isomer discrimination. Our data suggests that SIFT‐MS may be a useful tool for the rapid analysis of these compounds in plants and derived foodstuffs. Copyright © 2010 John Wiley & Sons, Ltd.     

Autocatalytic oxidation of β‐alanine by peroxomonosulfate in the presence of copper(II) ion

Kinetics and mechanism of oxidation of β‐alanine by peroxomonosulfate (PMS) in the presence of Cu(II) ion at pH 4.2 (acetic acid/sodium acetate) has been studied. Autocatalysis was observed only in the presence of copper(II) ion, and this was explained due to the formation of hydroperoxide intermediate. The rate constant for the catalyzed (k) and uncatalyzed (k) reaction has been calculated. The kinetic data obtained reveal that both the reactions are first order with respect to [PMS]. k values initially increase with the increase in [β‐alanine] and reach a limiting value, but k values decrease with the increase in [β‐alanine]. k values increase linearly with the increase in [Cu(II)], whereas k values increase with [Cu(II)]². Furthermore, k values are independent of [acetate], but k values decrease with the increase in acetate. A suitable mechanism has been proposed to explain the experimental observation. The reaction has been studied at different temperatures, and the activation parameters are calculated. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 40: 44–49, 2008     

Structure and dissociation energy of weakly bound H (n = 5−8) complexes

The geometrical parameters, vibrational frequencies, and dissociation energies for H (n = 5–8) clusters have been investigated using high level ab initio quantum mechanical techniques with large basis sets. The highest level of theory employed in this study is TZ2P CCSD(T). The C₁ structure of H is predicted to be a global minimum, while the C_s structure of H is calculated to be a transition state. Harmonic vibrational frequencies are also determined at the DZP and TZ2P CCSD levels of theory. The dissociation energies, D_e, for H (n = 5–8) have been predicted using energy differences at each optimized geometry, and zero‐point vibrational energies (ZPVEs) are considered to compare with experimental values. The dissociation energies (D_o) have been predicted to be 1.69, 1.65, 1.65, and 1.46 kcal · mol for H, H, H (C₁ symmetry) and H, respectively, at the TZ2P CCSD(T) level of theory. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

New simple method of measuring the surface glass transition temperature of polymers

A lap‐shear joint mechanical testing method has been probed to measure the surface glass transition temperature (T) of the thick bulk films of high‐molecular‐weight polymers. As T, the temperature transition “occurrence of autoadhesion–nonoccurrence of autoadhesion” has been proposed. The influence of chain flexibility, of molecular architecture, of polymer morphology, and of chain ends concentration on the T has been investigated. The correlation between the reduction in T with respect to the glass transition temperature of the bulk (T) and the intensity of the intermolecular interaction in the polymer bulk in amorphous polymers has been found. The effect of surface roughness on T has been discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2012–2021, 2010     

Quantification of methane in humid air and exhaled breath using selected ion flow tube mass spectrometry

In selected ion flow tube mass spectrometry, SIFT‐MS, analyses of humid air and breath, it is essential to consider and account for the influence of water vapour in the media, which can be profound for the analysis of some compounds, including H₂CO, H₂S and notably CO₂. To date, the analysis of methane has not been considered, since it is known to be unreactive with H₃O⁺ and NO⁺, the most important precursor ions for SIFT‐MS analyses, and it reacts only slowly with the other available precursor ion, O. However, we have now experimentally investigated methane analysis and report that it can be quantified in both air and exhaled breath by exploiting the slow O/CH₄ reaction that produces CH₃O ions. We show that the ion chemistry is significantly influenced by the presence of water vapour in the sample, which must be quantified if accurate analyses are to be performed. Thus, we have carried out a study of the loss rate of the CH₃O analytical ion as a function of sample humidity and deduced an appropriate kinetics library entry that provides an accurate analysis of methane in air and breath by SIFT‐MS. However, the associated limit of detection is rather high, at 0.2 parts‐per‐million, ppm. We then measured the methane levels, together with acetone levels, in the exhaled breath of 75 volunteers, all within a period of 3 h, which shows the remarkable sample throughput rate possible with SIFT‐MS. The mean methane level in ambient air is seen to be 2 ppm with little spread and that in exhaled breath is 6 ppm, ranging from near‐ambient levels to 30 ppm, with no significant variation with age and gender. Methane can now be included in the wide ranging analyses of exhaled breath that are currently being carried out using SIFT‐MS. Copyright © 2010 John Wiley & Sons, Ltd.     

Adaptation of a proton transfer reaction mass spectrometer instrument to employ NO+ as reagent ion for the detection of 1,3‐butadiene in the ambient atmosphere

A proton transfer reaction mass spectrometer (PTR‐MS) instrument was adapted to employ NO⁺ as a chemical reagent ion without any hardware changes by switching the reagent ion source gas from water vapor to dry air. Ionization of dry air within the hollow cathode ion source generates a very intense source of NO⁺ with only a minor impurity of NO. The intensities of the primary NO⁺ reagent ion and the unwanted impurity NO are controllable and dependent on the operational conditions of the hollow cathode ion source. Ion source tuning parameters are described, which maintain an intense source of NO⁺ while keeping the impurity NO signal to less than 2% of the total reagent ion intensity. This method is applied to the detection of 1,3‐butadiene. NO⁺ reacts efficiently with 1,3‐butadiene via a charge exchange reaction to produce only the molecular ion, which is detected at m/z 54. Detection sensitivities of the order of 45 pptv for a 1‐s measurement of 1,3‐butadiene are demonstrated. We present the first real‐time on‐line sub parts per billion measurement of 1,3‐butadiene in the ambient atmosphere. The only likely interference is from 1,2‐butadiene. Concurrent measurements of benzene are provided and suggest that the vehicular emissions are the predominant source of 1,3‐butadiene in a suburban Boston area monitoring location. Copyright © 2009 John Wiley & Sons, Ltd.     

Probing the ultrafast photoelectron spectra of Br2 molecule

The time‐dependent‐wave‐packet method is applied to study the ionization of Br₂ molecule with four ionization processes. The ground state absorption makes the photoelectron to be left in the three final ionic states: Br (X²∑), Br (A²∏_u), and Br (B²∑), and each population of these ionic states is related with the laser intensities. The information of the dissociation can be got by analyzing the photoelectron features of the transient wave packet, which also suggests that an ionization process occurs during the dissociation, and the Br atoms that mainly resulted from the dissociation of Br₂ (C¹∏_u) are ionized at later time delays as the dissociation is nearly complete. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

A method to calculate the one‐electron reduction potentials for nitroaromatic compounds based on gas‐phase quantum mechanics

Nitroaromatic compounds (NACs) are widespread environmental contaminants, and the one‐electron reduction potential (E) is an important parameter used in modeling their environmental fate. We have identified a method that is both accurate and efficient to predict E values for NACs, using gas‐phase quantum mechanics (QM) calculations combined with empirical correlations. First, the adiabatic electron affinity (EA) at 0 K is calculated using the B98/MG3S method, and the predictions are scaled by a factor of 0.802 to account for systematic errors in the density functional calculations. Second, the E values are predicted from a linear correlation between E and EA. Using this method, E values were predicted with a mean absolute deviation from measured values of 0.021 V for the 14 NACs used to obtain the correlation and 0.029 V for six additional NACs. This represents a substantial improvement in accuracy over predictions by other QM methods, which are affected by large errors in solvation or aqueous‐phase calculations for some compounds. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010.     

Energy‐resolved depth profiling of metal‐polymer interfaces using dynamic quadrupole secondary ion mass spectrometry

Quadrupole secondary ion mass spectrometry (qSIMS) characterization of a metallized polypropylene film used in the manufacturing of capacitors has been performed. Ar⁺ primary ions were used to preserve the oxidation state of the surface. The sample exhibits an incomplete metallization that made it difficult to determine the exact location of the metal‐polymer interface due to the simultaneous contribution of ions with identical m/z values from the metallic and the polymer layers. Energy filtering by means of a 45° electrostatic analyzer allowed resolution of the metal‐polymer interface by selecting a suitable kinetic energy corresponding to the ions generated in the metallized layer but not from the polymer. Under these conditions, selective analyses of isobaric interferences such as ²⁷Al⁺ and ²⁷C₂H or ⁴³AlO⁺ and ⁴³C₃H have been successfully performed. Copyright © 2009 John Wiley & Sons, Ltd.     

The lowest order relativistic corrections for the hydrogen molecule

We have calculated the lowest order relativistic corrections for the X ¹Σ, B¹Σ, a³Σ, b³Σ, I¹Π_g, C¹Π_u, i³Π_g, c³Π_u, J¹Δ_g, and j³Δ_g states of the hydrogen molecule using variational Monte Carlo methods and compact, explicitly correlated trial wavefunctions. Our values are in good agreement with earlier calculations on the X¹Σ and B¹Σ states. For the other states, our work provides the first estimate of these properties. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Solvation Chemistry of DL‐Nor‐Valine in Aqueous Mixture of Dipolar Aprotic N,N‐Dimethyl Formamide

In this article, we reported the solubilities of the amino acid DL‐nor‐valine (VAL) at five equidistant temeratures i.e. from 15 to 35 °C in aqueous mixtures of N,N‐dimethyl formamide (DMF). The Standard free energies (ΔG (i)) and entropies (ΔS (i)) of transfer of VAL from water to aqueous mixture of cationophilic dipolar aprotic DMF have been evaluated at 25 °C. The transfer of Gibbs energies (ΔG (i)) and entropies (TΔS (i)) due to the chemical effects have been obtained after elimination of cavity effect, estimated by the scaled particle theory and dipole‐dipole interaction effects, computed by the used of Keesom‐orientation expression. The chemical contribution of transfer energetics of DL‐nor‐valine (VAL) are mainly guided by the composite effects of increased dispersion interaction, basicity effect and decreased acidity, hydrogen bonding effects, hydrophilic hydration and hydrophobic hydration of aqueous DMF mixtures as compared to that of reference solvent, water.     

Mechanistic investigation of vibrational fine structure in e‐H2 scattering using local complex potential‐based time dependent wave packet approach

The structural features of vibrational excitation cross‐sections in resonant e‐H₂ scattering have been investigated using a time dependent wave packet approach and a local complex potential to describe the ²Σ H anion. An analysis of the partial contributions to the vibrational excitation cross‐sections reveals that all features of the excitation profile result from simple interference between bound vibrational levels of H₂ and H. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008