Role of electronic partition function in quantitative SIMS using the Saha-Eggert equation

Methods of obtaining the electronic partition functionsZ were discussed with an intention to use them for the Saha-Eggert quantification in SIMS. The Lagrange's interpolation formula and the least-squares method were applied to the published values ofZ to obtain the expression for calculatingZ at arbitrary temperatures. With the aid of the Saha-Eggert equation, the secondary-ion currents from Ni-Cr and Fe-Ni-Cr alloys were converted into the elemental concentrations for the two types ofZ: those obtained with the above methods and those with the approximate fifthorder polynomials presented by de Galan and others. It was proved, from the comparison of the calculated concentrations, that the latter are valid for the quantification in SIMS using the Saha-Eggert equation. The largest error in the elemental concentrations was 22% for the Ni-Cr alloy and 7% for the Fe-Ni-Cr alloy.     

Factors affecting immonium ion intensities in the high-energy collision-induced decomposition spectra of peptides

Each amino acid in a peptide has a characteristic immonium ion (H₂N⁺?CHR), the presence of which in a mass spectrum can indicate the presence of that amino acid. High-energy collision-induced decomposition studies on small peptide ions formed by fast atom bombardment showed the relative intensities of these immonium ions to be dependent on the relative positions of the amino acids in the peptide chain: C-terminal, N-terminal or in-chain. Evidence in favour of competition in the formation of immonium ions is presented.     

Mixed-ligand complexes of iron(II), iron(III), copper(II), and cobalt(II) with pyrazolonic and 2,2′-bipyridine ligands

New mixed-ligand complexes, [M₂(BAMP)(bipy)₂][MCl₄]₂, M=Co⁺²(1), Cu⁺²(2), [M₂(TAMEN)(bipy)₂][MCl₄]₂, M=Fe⁺²(3), Co²⁺(4), and [Fe₂(TAMEN)(bipy)₂][FeCl₆]₂ (5), where BAMP and TAMEN stand for the Mannich bases N,N′-bis(antipyryl-4-methylene)-piperazine and N,N′-tetra(antipyryl-4-methylene)-1,2-ethane-diamine, respectively, have been obtained and characterized by elemental analyses, conductometric and magnetic susceptibility measurements at room temperature, mass spectrometry, UV-Vis, infrared, and mass spectroscopy, and ¹H NMR spectra for the ligands.     

Degradation of poly(acrylates) under SF5+ primary ion bombardment studied using time‐of‐flight secondary ion mass spectrometry. 2. Poly(n‐alkyl methacrylates)

Polyatomic primary ions offer low penetration depth and high damage removal rates in some polymers, facilitating their use in the molecular depth profiling of these polymers by secondary ion mass spectrometry (SIMS). This study is the second in a series of systematic characterizations of the effect of polymer chemistry on degradation under polyatomic primary ion bombardment. In this study, time‐of‐flight SIMS (ToF‐SIMS) was used to measure the damage of ～90 nm thick spin‐cast poly(methyl methacrylate), poly(n‐butyl methacrylate), poly(n‐octyl methacrylate) and poly(n‐dodecyl methacrylate) films under extended (～2 × 10¹⁴ ions cm^?2) 5 keV SF₅⁺ bombardment. The degradation of the poly(n‐alkyl methacrylates) were compared to determine the effect of the length of the alkyl pendant group on their degradation under SF₅⁺ bombardment. The sputter rate and stability of the characteristic secondary ion intensities of these polymers decreased linearly with alkyl pendant group length, suggesting that lengthening the n‐alkyl pendant group resulted in increased loss of the alkyl pendant groups and intra‐ or intermolecular cross‐linking under SF₅⁺ bombardment. These results are partially at variance with the literature on the thermal degradation of these polymers, which suggested that these polymers degrade primarily via depolymerization with minimal intra‐ or intermolecular cross‐linking. Copyright © 2004 John Wiley & Sons, Ltd.     

3D analysis of solids using sputtered MCs+ ions

The 3-dimensional characterization of solids by means of secondary-ion mass spectrometry is investigated. Monitoring MCs⁺ molecular ions emitted from surfaces upon Cs⁺ bombardment, laterally-resolved ion images were recorded with acquisition times of typically a few seconds which exhibit a dynamic sensitivity range in excess of 10² and a lateral resolution of about 2–3 μm. A quantitative data evaluation via relative sensitivity factors (RSFs) transforms them into elemental distribution maps. From the applied RSFs, local (i.e. erosion-time dependent) sputtering yields can be derived; together with atomic densities (which might be interpolated from pure-element values) a local depth scale (relative to some reference level) is assigned to each pixel of the 3D data volume recorded during the analysis. In conjunction with the elemental concentration values, this provides the possibility of a complete reconstruction of the 3D sample volume removed by sputtering. This approach is exemplified by means of a laterally inhomogeneous semiconductor test specimen.     

Experimental and theoretical determination of the mixing efficiency at low‐energy Ar+ bombardment: case study of the Cu/Co system

The mixing of a Co/Cu bilayer induced by low‐energy ion bombardment was studied by AES depth profiling and molecular dynamic (MD) simulation. The conditions of the ion bombardment were as follows: Ar⁺ ion, 1 keV energy, 82° angle of incidence (with respect to the surface normal). In AES depth profiling, the in‐depth concentration distribution was estimated from the measured Auger intensities assuming that the in‐depth distribution is an erf function. The variance (σ²) of the erf function gave the broadening of the interface due to ion bombardment, which divided by the fluence (Φ) and deposited energy (F_D given by SRIM) gave the mixing efficiency (σ²/ΦF_D) to be 0.08 ± 0.01 nm⁵/keV. The mixing efficiency calculated by MD, 0.09 nm⁵/keV, agreed well with that estimated from the experimental data, and both have been close to the value assuming ballistic mixing. Copyright © 2007 John Wiley & Sons, Ltd.     

An effect of N ion bombardment on the properties of CdTe thin films

E-beam evaporated CdTe thin films were processed with N⁺ ion bombardment as in situ process. The N⁺ ion glow was generated using simple Multipurpose Al probe instead of conventional plasma sources. The prepared films were identified as nano crystalline using XRD analysis. High N⁺ ion fluence helped to grow (3 1 1) oriented CdTe thin films instead of (2 2 0) and (1 1 1). The observed results revealed the effect of N⁺ ion fluence on the structural parameters like lattice parameter, d space value, crystalline size, dislocation density, micro strain etc. The observed optical band gap values lie in between 1.47 and 1.77 eV. The effect of N⁺ ion bombardment on optical properties was also reported. Noticeable change in electrical and surface properties was also observed. The observed value shows the reproducibility as <1% and it is suggested that the N⁺ ion plasma was effectively utilized to modify the structural, optical and surface properties as in situ.     

XPS- and AES-investigations of electron and ion beam induced effects on SK16 glass surfaces

Summary Electron beam induced effects in the near surface region of SK16 glass samples (44% SiO₂, 25% B₂O₃, 28% BaO, 3% other) have been studied using Auger electron spectroscopy (AES) with 3 keV primary electrons at different current densities (4.7 mAcm^–2–75 mAcm^–2). It was found that the SiO₂ and B₂O₃ constituents dissociate during electron bombardment to form binding structures which are characteristic for elemental Si and B, respectively. To investigate the influence of the ion beam irradiation on the binding structure, the glass samples were bombarded with Ar⁺ ions of different kinetic energies (0.5 keV–5 keV), followed by XPS analysis. In comparison to the XPS signal of a virgin SK16 surface from a sample fractured in situ under UHV conditions, the FWHM of the photoelectron peaks were found to increase with the bombarding ion energy. Subsequent Auger spectra revealed that the ion bombardment also caused a dissociation of the SiO₂ and B₂O₃ components. Depending on the ion energy, a constant ratio between elemental and oxidized binding form is obtained.     

Tailoring and investigation of surface chemical nature of virgin and ion beam modified muscovite mica

We report that the surface chemical properties of muscovite mica [KAl₂(Si₃Al)O₁₀(OH)₂] like important multi-elemental layered substrate can be precisely tailored by ion bombardment. The detailed X-ray photoelectron spectroscopic studies of a freshly cleaved as well as 12-keV Ar⁺ and N⁺ ion bombarded muscovite mica surfaces show immense changes of the surface composition due to preferential sputtering of different elements and the chemical reaction of implanted ions with the surface. We observe that the K atoms on the upper layer of mica surface are sputtered most during the N⁺ or Ar⁺ ions sputtering, and the negative aluminosilicate layer is exposed. Inactive Ar atoms are trapped, whereas chemically reactive N atoms form silicon nitride (Si₃N₄) and aluminum nitride (AlN) during implantation. On exposure to air after ion bombardment, the mica surface becomes more active to adsorb C than the virgin surface. The adsorbed C reacts with Si in the aluminosilicate layer and forms silicon carbide (SiC) for both Ar and N bombarded mica surfaces. Besides the surface chemical change, prolonged ion bombardment develops a periodic ripple like regular pattern on the surface.     

Estimation of Silica Species’ Concentrations in Lithium and Magnesium Chloride Solutions from the Peak Intensities Observed by FAB-MS

The concentrations of dissolved silica species in electrolyte solutions were derived from the relative intensities of silica species, obtained from FAB-MS measurements (fast atom bombardment mass spectrometry), and the total concentration of dissolved silica. Generally, silica species in aqueous solutions form various complexes with cations such as sodium (Na⁺) or calcium (Ca²⁺), and it has been difficult to determine the concentration of each species. From the observed results from FAB-MS, the chemical species of silica dissolved in lithium chloride (LiCl) and magnesium chloride (MgCl₂) solutions do not include complexes with these cations, and thus Li⁺ and Mg²⁺ do not replace protons of the silanol groups in silica. Therefore, in LiCl and MgCl₂ solutions, all of the simple structures of silicate species can be identified. The concentration of each silica species was estimated on the basis of its mass spectra peak intensities and the total concentration of silica as determined by colorimetry. This study yields the concentration of each silica species within small errors, whereas conventional methods (such as ²⁹Si-NMR) have not yielded the concentrations of individual silica species. From these results, dimers and cyclic tetramers are concluded to be the main species in silica solutions with concentrations of at most 0.1 to 0.2 μmol⋅dm⁻³. This tendency should also occur in NaCl and CaCl₂ solutions, which are major electrolytes in natural waters.     

Quantification of Ion‐Pairing Effects on the Nucleophilic Reactivities of Benzoyl‐ and Phenyl‐Substituted Carbanions in Dimethylsulfoxide

Second‐order rate constants for the reactions of acceptor‐substituted phenacyl (PhCO?CH^??Acc) and benzyl anions (Ph?CH^??Acc) with diarylcarbenium ions and quinone methides (reference electrophiles) have been determined in dimethylsulfoxide (DMSO) solution at 20 °C. By studying the kinetics in the presence of variable concentrations of potassium, sodium and lithium salts (up to 10^?2 mol L^?1), the influence of ion‐pairing on the reaction rates was examined. As the concentration of K⁺ did not have any influence on the rate constants at carbanion concentrations in the range of 10^?4–10^?3 mol L^?1, the acquired rate constants could be assigned to the reactivities of the free carbanions. The counter ion effects increase, however, in the series K⁺<Na⁺<Li⁺, and the sensitivity of the carbanion reactivities toward variation of the counter ion strongly depends on the structure of the carbanions. The reactivity parameters N and s_N of the free carbanions were derived from the linear plots of log k₂ against the electrophilicity parameters E of the reference electrophiles, according to the linear‐free energy relationship log k₂(20 °C)=s_N(N+E). These reactivity parameters can be used to predict absolute rate constants for the reactions of these carbanions with other electrophiles of known E parameters.     

Chiral recognition and enantiomer assays of N-(3,5-dinitrobenzoyl)amino acid derivatives using electrospray ionization–mass spectrometry

A pair of pseudoenantiomers, anilide derivatives of N-pivaloylproline were prepared and used as chiral selectors for enantiomer discrimination of amides or esters of N-(3,5-dinitrobenzoyl)amino acids in single-stage electrospray ionization/mass spectrometric experiments. Addition of a chiral analyte to a solution of the two pseudoenantiomeric chiral selectors affords selector–analyte complexes in the electrospray ionization mass spectrum where the ratio of these complexes is dependent on the enantiomeric composition of the analyte. The relationship between the ratio of the selector–analyte complexes in the electrospray ionization mass spectrum and the enantiomeric composition of the analyte can be used to relate the extent of the measured enantioselectivity and for quantitative enantiomeric composition determinations. Effects of the added cationic ions (H⁺, Li⁺, Na⁺ and K⁺) and instrument conditions on the selector–analyte ion intensity and the enantioselectivity (α_MS) were investigated. The percent ratio of the sum of the selector–analyte ion counts and the total ion counts decreases accordingly with the increase of the desolvation temperature for H⁺, Na⁺ and K⁺. The ratio for Li⁺ kept almost constant. The best α_MS was observed at a desolvation temperature of 200 °C with the added H⁺. The cone voltage has little effects on the α_MS values though the intensities of selector–analyte complexes are decreased at higher cone voltages. The observed MS enantioselectivities are comparable to the HPLC enantioselectivities and the sense of chiral recognition by MS is consistent with what is observed chromatographically. Quantitative enantiomeric composition determinations for five different samples of N-(3,5-dinitrobenzoyl)leucinyl butylamide at four different concentrations were performed. The average % difference between the HPLC and MS enantiomer determinations is 6.8% and 3.7% for the calibration lines constructed at a concentration of the analyte of 125 μM and 12.5 μM, respectively.     

Mass spectrometry of stable free radicals—II: pyrrolidine nitroxides

3-Substituted-2,2,5,5-tetramethylpyrrolidine nitroxides are stable free radicals used extensively in the synthesis of ‘spin labels’. The high resolution mass spectra of these nitroxides substituted with ? CH₂OH, ? OH, ? NH₂ and ?o have been recorded on magnetic tape and the elemental compositions of the ions calculated by computer. Ionisation by electron bombardment(70eV), gives rise to an even-electron molecular ion species. [M+1]⁺. ions are observed in the spectra of all compounds examined, except in the case of the 3-carbonyl compound, 2,2,5,5-tetramethylpyrrolid-3-one-1-oxyl. Loss of a methyl radical from these ions leads to the appearance of ions at [M -14]⁺. The predominant fragmentation for those compounds in which the substituents can supply electrons to the ring, is the sequential elimination of isobutene, nitric oxide and a hydrogen radical. In the case of the 3-hydroxy compound, these ions account for 23 percent of the total ion current. 2,2,5,5-Tetramethylpyrrolid-3-one-1-oxyl, which bears an electron-withdrawing substituent gives rise to a fragmentation pattern somewhat different from those of the other compounds. The main features are the absence of a peak at [M + 1]⁺˙ and the general phenomenon of fewer peaks but with higher intensities.     

Studies on the effect of the cation nature on the kinetics of the isotopic exchange reaction between chloride ion and O,O-diphenylphosphorochloridothionate in acetonitrile

Rate constants and activation parameters for the isotopic exchange reactions between (PhO)₂PSCl and M³⁶Cl (M = Me₄N⁺, Et₄N⁺, n-Bu₄N⁺, Et₃HN⁺, EtH₃N⁺, Li⁺) in acetonitrile were measured in order to find the effect of the cation nature onthe kinetics of the reaction. The rate constants measured for a range of concentrations of Et₃HN³⁶Cl, EtH₃N³⁶Cl, and Li³⁶Cl were analyzed using the Acree equation. The equivalent conductance of LiCl in acetonitrile was determined. The nature of the cation has no effect on the mechanism of the reaction. The cation changes only the experimental rate constant proportionally to the dissociation degree of the salt. Smaller values of the rate constant and smaller activation parameters ΔH? and ΔS? for the reaction with Li³⁶Cl indicate the existenceof the intermolecular interaction between lithium ions and O,O-diphenylphosphorochloridothionate.     

Parallel detection,quantification, and depth profiling of peptides with dynamic-secondary ion mass spectrometry (D-SIMS) ionized by C60–Ar co-sputtering

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) using pulsed C₆₀⁺ primary ions is a promising technique for analyzing biological specimens with high surface sensitivities. With molecular secondary ions of high masses, multiple molecules can be identified simultaneously without prior separation or isotope labeling. Previous reports using the C₆₀⁺ primary ion have been based on static-SIMS, which makes depth profiling complicated. Therefore, a dynamic-SIMS technique is reported here. Mixed peptides in the cryoprotectant trehalose were used as a model for evaluating the parameters that lead to the parallel detection and quantification of biomaterials. Trehalose was mixed separately with different concentrations of peptides. The peptide secondary ion intensities (normalized with respect to those of trehalose) were directly proportional to their concentration in the matrix (0.01–2.5 mol%). Quantification curves for each peptide were generated by plotting the percentage of peptides in trehalose versus the normalized SIMS intensities. Using these curves, the parallel detection, identification, and quantification of multiple peptides was achieved. Low energy Ar⁺ was used to co-sputter and ionize the peptide-doped trehalose sample to suppress the carbon deposition associated with C₆₀⁺ bombardment, which suppressed the ion intensities during the depth profiling. This co-sputtering technique yielded steadier molecular ion intensities than when using a single C₆₀⁺ beam. In other words, co-sputtering is suitable for the depth profiling of thick specimens. In addition, the smoother surface generated by co-sputtering yielded greater depth resolution than C₆₀⁺ sputtering. Furthermore, because C₆₀⁺ is responsible for generating the molecular ions, the dosage of the auxiliary Ar⁺ does not significantly affect the quantification curves.     

GC-MS of amino acids as their trimethylsilyl/t-butyldimethylsilyl Derivatives: In model solutions III

Summary Fragmentation patterns of the essential amino acids (AAs) as their silyl derivatives have been obtained with the aid of ion trap detection (ITD). Three derivatizing reagents, hexamethyldisilazane+trifluoroacetic acid (HMDS+TFAA),bis-(trimethylsilyl)trifluoroacetamide (BSTFA) andN-methyl-N-(t-butyldimethylsilyl)trifluoroacetamide (MTBSTFA) were used. Simple and multiple derivatives obtained with each reagent have been investigated, with regard to their sensitivity and selectivity. Our study performed in the concentration range of 5-2000 ng amino acids has shown that, contrary to literature data, thirteen of the twenty-two AAs investigated including the TBDMS derivatives give rise to more than one peak when eluted. As a result of ion/molecule interaction the very informative ions of high masses, ([M]⁺, [M+TMS/(TBDMS)]⁺, [M+1]⁺) are formed with considerable intensities. The fragments [M-CH₃]⁺, [M-C₄H₉]⁺, [M-(CH₃)₂Si]⁺, [M-TMS/(TBDMS)COO]⁺, [M-TBDMSOH]⁺, [M-TBDMSO]⁺, [M-TBDMSNH]⁺ and numerous others could be utilized for identification purposes. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Enhanced extract preparation of native manganese and iron species from brain and liver tissue

To date, no reference method for the extraction of labile Mn species from biological tissues is published which provides sufficient extraction efficiency combined with monitoring speciation. Here, an extraction method is reported using cryogenic conditions (+N) under inert gas atmosphere. Fresh brain and liver tissues were used, then stored either 1 day (+N) or 1 month in N_2liq (+N 1 m) to evaluate degradation effects during long-term storage. Both attempts were compared to a previous extraction method (−N) using neither N_2liq nor storage ability. Mn and Fe concentrations in extracts and pellets were determined with inductively coupled plasma (ICP)-atomic emission spectroscopy (AES) and compared to acid digests of the same sample. Element ratios of extracts/digest indicated the extraction efficiency, which was increased from 17% (−N) to 26% (+N) for Mn in brain or from 28% (−N) to 44% (+N) in liver extracts. For Fe species, the increase was only from 40% (−N) to 44% (+N) in brain but from 64% (−N) to 74% (+N) in liver. Size exclusion chromatography (SEC)-ICP-mass spectrometry (MS) was employed to screen for Mn and Fe species pattern in extracts. In brain, surplus extracted Mn (+N, +N 1 m) was assigned to organic Mn species, mainly from the 0.7–4 kDa fraction, while in the liver, it was seen in the 70–80 kDa fraction. Fe speciation was similar for −N and +N methods in brain extracts. In liver, higher amounts of Fe species were extracted from the 140–160 kDa fraction. Storage at −196 °C for 1 month did neither affect Mn speciation in brain nor in liver extracts. Fe species pattern showed a negligible shift (≤5%) from 140–160 to 70–80 kDa fraction in liver extracts stored 1 month in N_2liq.     

Synthesis,crystal structure and fluorescence properties of two dinuclear zinc(II) complexes incorporating tridentate (NNO) Schiff bases

Reactions of hydrated zinc(II) trifluoroacetate and sodium azide with two tridentate Schiff bases HL¹ (2-((E)-(2-(dimethylamino)ethylimino)methyl)-4-chlorophenol) and HL² (2-((E)-(2-(dimethylamino)ethylimino)methyl)-4-bromophenol) under the same reaction conditions yielded two dinuclear isostructural zinc(II) complexes, [Zn(L¹)(N₃)]₂ (1) and [Zn(L²)(N₃)]₂ (2), respectively. The complexes were characterized systematically by elemental analysis, UV–Vis, FT-IR, and ¹H NMR spectroscopic methods. Single-crystal X-ray diffraction studies reveal that each of the dinuclear complexes consists of two crystallographically independent zinc(II) ions connected by double bridging phenoxides. All zinc(II) ions in 1 and 2 are surrounded by similar donor sets and display distorted square–pyramidal coordination geometries. The ligands and complexes reveal intraligand ¹(π → π*) flourescence. The enhancement of the fluorescence intensities for the complexes compared to the ligands indicates their potential to serve as photoactive materials.     

Determination of traces of boron in semiconductor amorphous silicon film by filament-vaporization inductively-coupled plasma/atomic emission spectrometry

Silicon is dissolved from the platinum substrate by nitric/hydrofluoric acids. The recovery of boron on direct analysis was poor, but was increased to >95% by the addition of 500–5000 μg ml^?1 phosphorus as phosphoric acid. The results compared well with the molar ratio of the gases (B₂H₆/(Ar + H₂) used to form the film and the intensity ratio of ¹¹B⁺ and ³⁰Si⁺ obtained by secondary-ion mass spectrometry.     

Analysis of tetrabenzyl N-giucosidic,N-mannosidic and N-galactosidic Isomers using fast atom bombardment/mass-analysed ion kinetic energy spectrometry

A series of new synthetic tetrabenzyl N-glucosidic, N-mannosidic and N-galactosidic isomers were investigated by fast atom bombardment (FAB)/mass-analysed ion kinetic energy (MIKE) spectrometry. The [M + H]⁺ ions were obtained with high abundance in the FAB spectra when using 3-nitrobenzyl alcohol as the matrix. The FAB/MIKE spectra provide characteristic daughter ions fragmented from selected molecular parent ions, allowing these isomers to be differentiated. In addition, an interesting rearrangement was found from the MIKE spectra, indicating that the benzyl (Bzl) group on the sugar ring is rearranged on to the N atom of the base (R) group to form [R + Bzl + H]⁺ and [R+ 2Bzl]⁺ ions.