Secondary Ion Mass Spectra Research Articles

Interchain ion formation in secondary ion mass spectrometry resulting from the double-helical structure of isotactic poly(methyl methacrylate) in adsorbed monolayers

Results from time-of-flight secondary ion mass spectra (TOF-SIMS) of Langmuir-Blodgett monolayers of various isomers (isotactic and syndiotactic) of poly(methyl methacrylate) (PMMA) are reported. A detailed analysis of the repeating pattern of fragment ion clusters yields very different patterns for isotactic PMMA LB layers than for the syndiotactic and atactic forms. This is attributed to the resulting double-helical tertiary structure of isotactic PMMA, a structure that does not form for the syndiotactic and atactic PMMA polymer monolayers. The double-helical structure of isotactic PMMA monolayers is verified using reflection absorption Fourier transform infrared spectroscopy. The repeating patterns of cluster ions in syndiotactic and atactic PMMA monolayers can be explained using statistical chain-breaking models for fragmentation of single isolated polymer chains. The repeating ion patterns from the TOF-SIMS of the isotactic PMMA monolayers are analyzed by considering bond breaking and ion formation between adjacent polymer chains, resulting in a newly proposed ion formation model due to the tertiary structure of the double-helical form. A rearrangement mechanism consistent with all ions that are formed is proposed.

Antibodies to GM1(NeuGc) in Guillain–Barré syndrome after ganglioside therapy

N-Glycolylneuraminic acid-containing GM1 [GM1(Gc)] is a molecule for serum antibodies in patients with Guillain–Barré syndrome (GBS). To clarify the pathogenesis of GBS after treatment with bovine brain ganglioside, we investigated the presence of anti-GM1(Gc) antibody in patients who developed GBS after ganglioside injection. Serum samples were taken from nine Italian patients with GBS after ganglioside therapy as well as from untreated Italian (n=30) and Japanese (n=131) GBS patients. Bovine brain gangliosides fractionated in a column were used as antigens, and binding of serum IgG or IgM was examined. An absorption study of IgG anti-GM1(Gc) antibody was made with GM1, asialo-GM1, GM2, GD1a, and GD1b. Four of the nine patients who developed GBS after being administered gangliosides had IgG anti-GM1(Gc) antibodies. Anti-GM1(Gc) IgG antibody frequencies were higher in patients with GBS after ganglioside therapy than in those who were untreated. Rates of absorption of IgG anti-GM1(Gc) antibodies by GM1 were significantly higher (except for asialo-GM1 and GD1b) than by GM2 and GD1a. The presence of GM1(Gc) was confirmed in bovine brain immunochemically using cholera toxin and Hanganutziu–Deicher antibody. Secondary ion mass spectra showed that the structure of the ganglioside was consistent with that of GM1(Gc). GM1(Gc) was recognized more frequently in sera from patients who developed GBS after ganglioside therapy than in sera from untreated GBS patients. Because N-glycolylneuraminic acid-containing gangliosides seem to be highly immunogenic in humans, GM1(Gc) may act as an immunogen in some patients who develop GBS following ganglioside therapy.

Kiloelectronvolt Particle-Induced Emission and Fragmentation of Polystyrene Molecules Adsorbed on Silver: Insights from Molecular Dynamics

Polystyrene oligomers adsorbed on Ag{111} have been used as a model system for a molecular dynamics study of polyatomic fragment ejection from large organic adsorbates on metals. The simulation of the interaction between the incident 500 eV Ar atoms and the sample predicts the nature and kinetic energy of the characteristic fragments observed in the low-mass range of the experimental polystyrene secondary ion mass spectrum (SIMS). This agreement confirms that characteristic molecular fragments can be the result of a collisional emission process. Moreover, the results indicate that the ejection of intact molecules occurs frequently. To understand the mechanisms of emission of fragments and parent molecules, a representative set of trajectories has been analyzed in detail. The ejection of characteristic fragments is primarily due to the direct interaction between the primary particle and the organic adsorbate. In contrast, desorption of intact molecules is induced by collision cascades in the sample surface. The emission of energetic intact molecules is best explained by a cooperative uplifting mechanism in which substrate atoms with similar momenta push the molecule upward. For comparison to the 500 eV bombardment conditions, simulations conducted with 5 keV primary particles show that large-scale simultaneous motions in the substrate may also occur, inducing the emission of many silver atoms and organic molecules in a single high action event.

Secondary ion mass spectrometry in studies of occupational dust particles from plants with nuclear fuel cycle

Secondary ion mass spectra recorded on sputtering individual particles of occupational dust emitted by nuclear plants carry information about the chemical composition of the microsamples. Along with the data of isotopic analysis, the data of secondary ion mass spectrometry enables one to judge the function of the materials and the character of processes occurred at the plant. The efficiency of the procedure is demonstrated by the results of analyses of real samples selected by inspectors of the International Atomic Energy Agency at plants with nuclear fuel cycle

Defect analysis of Cl2/HBr/He/O2 etching process by imaging time-of-flight secondary ion mass spectrometry

Defects appeared during Cl2/HBr/He/O2 etching process were investigated by high laterally resolved imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS). The defects with size of one to several microns appeared after the etching process. These defects are electron-beam sensitive during Auger electron spectroscopy and energy dispersive spectrometry analysis. Imaging TOF-SIMS clearly shows that the defect consists of bromine and H2O. Relatively weak oxygen and silicon signals were detected from the defect site. A negative secondary ion mass spectrum from region of interest (ROI) analysis of the defect area shows a very strong Br− signal. A positive secondary ion mass spectrum from ROI analysis has a very strong H2O+ signal from the defect. These results amply demonstrate that imaging TOF-SIMS enables chemical analysis of small defect at outmost surface with high lateral resolution and submonolayer sputtering damage under static SIMS analytical conditions.

Growth of ZnS : Tm thin films by MOCVD

Thin films of thulium-active ZnS have been deposited on ITO coated glass substrates by a low-pressure vertical metalorganic chemical vapor deposition (MOCVD) system. Dimethylzinc (DMZn) and hydrogen sulfide (H 2S) are used as reactants, and Tris(hexafluoroacetonato-thulium) (Tm(HFAA) 3, molecular formula Tm(C 5HF 6O 2) 3) is used as dopant source. Energy dispersive spectrometer (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM), Auger electron spectra (AES), and secondary ion mass spectra (SIMS) were used to determine the elemental composition, surface morphologies and depth profiles. Optical properties of ZnS : Tm thin films were characterized by photoluminesence (PL). The best growth conditions are substrate temperature at 225°C, DMZn bubbler temperature at −8°C, Tm(HFAA) 3 bubbler temperature at 70°C, growth pressure at 30 Torr, flow rate of DMZn 2.5×10 −5 mol/min, flow rate of H 2S 5×10 −4 mol/min, flow rate of Tm(HFAA) 3 0.1 SLM, and VI/II molar ratio of 20.

Evidence of simple intramolecular rearrangement at polymer end groups in secondary ion mass spectrometry.

Polystyrenes with various end groups were analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS). These end groups were obtained by termination of the active anionic group by sulfonate or chlorosilane derivatives. Characteristic end group fragments for each sulfonate derivative were observed. On the one hand, for PS capped by methyl sulfonate, or -(CH(2))(4)-O-SO(2)-CH(3), almost complete end group fragment is observed at m/z 95 and a [O-SO(2)-CH(3)](-) molecular structure. On the other hand, when PS is terminated by silyl methyl sulfonate, or -Si(CH(3))(2)-(CH(2))(3)-O-SO(2)-CH(3), the most characteristic fragment in the fingerprint secondary ion mass spectrum is located at m/z 153 with [Si(CH(3))(2)-O-SO(2)-CH(3)](+) and the complete end group peak, [Si(CH(3))(2)-(CH(2))(3)-O-SO(2)-CH(3)](+), at m/z 201, is absent. According to the molecular structure, characteristic end group secondary ions can be emitted as complete or rearranged fragments. Various silylalkyl alcohol or sulfonate functionalities are analyzed and fragmentation pathways are discussed. To our knowledge, this is the first time that such rearrangement at silyl functions has been observed and demonstrated in fingerprint secondary ion mass spectra. Copyright 1999 John Wiley & Sons, Ltd.

Studies of complexation of metal cations by tris(3,6-dioxaheptyl)amine in solution

The complexation of some cations (Zn2+, Fe2+, Fe3+, Ni2+, Cu2+, Co2+, Pb2+, Na+, Li+, Mn2+, Cd2+, K+, Mg2+, Cr3+) by tris(3,6-dioxaheptyl)amine in various solvents was studied by the thin layer chromatography, liquid secondary ion mass spectra, FT-IR and 13C NMR spectroscopies as well as kinetic methods. In this article, the structure of the complexes is discussed.

The effect of boron ion implantation and annealing on the microstructure and electrical characteristics of the diamond films

Diamond films were doped by boron ion-implantation with the energy of 120 keV. The implantation dose ranged from 10 14 to 10 17 cm −2. After the implantation, the diamond films were annealed at different temperatures (600–750°C) for different times (2–15 min). Scanning Electronic Microscope, Raman and Secondary Ion Mass-spectrum were used to investigate the effect of boron ion implantation and annealing on the microstructure of the diamond films. The electrical resistivities of the diamond films were also measured. It was found that the best dose of boron ion-implantation into the diamond film was around 10 16 cm −2. The appropriate annealing temperature and time was 700°C and 2–5 min, respectively. After implantation, the resistivities were reduced to 0.1 Ω cm (almost nine orders lower than the unimplanted diamond films). These results show that boron ion implantation can be an effective way to fabricate P-type diamond films.

Organic substances in cometary grains: comparison of secondary ion mass spectral data and californium-252 plasma desorption data from reference compounds

Secondary ion mass spectra (SIMS) and 252Cf plasma desorption ionization mass spectra (PDMS) of two carboxylic acids and two purine nucleobases have been compared. Results demonstrate that the positive ion mass spectra as well as the negative ion mass spectra are very similar in SIMS and PDMS. The principal characteristics are formation of quasimolecular ions (M + H) + or (M−H) − and loss of small molecules producing nonradical fragment ions; fumaric acid exhibits a remarkable formation of radical cations and anions. A set of simplified rules has been formulated for typical ion production processes involved in these techniques. This work contributes to the development of methods for data interpretation applicable to in situ analyses of cometary grains during the ROSETTA space mission of European Space Agency to the comet 46p/Wirtanen.

Quadrupole secondary ion mass spectrometer for simultaneous detection of positive and negative ions

The purpose of this study was to design a quadrupole secondary ion mass spectrometer for simultaneous detection of both positive and negative ions of different mass. An original setup based on a quadrupole electrostatic deflector configuration that allows energy and spatial separation of all types of secondary ions was proposed. The device was modeled using the SIMION 3D program before building the prototype. Trajectory and acceptance calculations were provided. Positive and negative secondary ion mass spectra for molybdenum test samples were obtained. Copyright © 1999 John Wiley & Sons Ltd.

Identification of flavonoid diglycosides in yellow lupin (Lupinus luteus l.) with mass spectrometric techniques

Various mass spectrometric techniques were used for the structural elucidation of flavonoid glycosides isolated from green parts of yellow lupin plants (Lupinus luteus). A methodological approach is proposed consisting of (1) extraction and purification of flavonoid glycosides from plant tissues, (2) registration of liquid secondary ion mass spectra of intact compounds and (3) gas chromatographic/mass spectrometric analyses of those compounds subjected to several types of chemical modification. On the basis of these data, it was possible to define the molecular mass of the glycosides, the structure of the aglycones, the configuration of sugar moieties and the position of glycosidic linkages between sugars in diglycosides or between aglycone and sugar moieties. Analysis of the mass spectrometric data permitted structural identification of four flavonoid diglycosides, where the aglycones had flavone, isoflavone and flavonol structures. They were recognized as: apigenin 7-O-(2″-O -rhamnopyranosyl)glucopyranoside (1), genistein 4′,7-O-diglucopyranoside (2), kaempferol 3-O -(6″-rhamnopyranosyl)glucopyranoside (3) and 3′- or 4′-methylquercetin 3-O-(6″-O -rhamnopyranosyl)glucopyranoside (4). Complete structural evaluation of flavonoid glycosides was possible with only submilligram quantities of samples needed to register various mass spectra. It was not possible, however, to define the anomeric configuration of the C-1 carbons in investigated glycosides. Copyright © 1999 John Wiley & Sons, Ltd.

Chiral recognition and the determination of optical purity of a-phenylethylamine using monosaccharide as a chiral selector under liquid secondary ion mass spectral conditions

Naturally available monosaccharides, D-mannose, D-galactose and D-glucose, have been used for the first time as chiral co-matrices for chiral recognition of α -phenylethylamine. The liquid secondary ion (LSI) mass spectra of a mixture of D-mannose and (R)- or (S)α -phenylethylamine in the presence of benzylamine as reference compound and glycerol as matrix showed [(mannose + (R)- / (S)-α phenylethylamine + H) – H2O] + (a) and [(mannose + benzylamine + H)–H2O] + (b) ions. The significant difference was observed in the relative peak intensity (RPI) values calculated from the ion abundances of ion a and b. The RPI values for (R)- and (S)-α phenylethylamine are RPIR = 0.79 and RPIS = 1.34, respectively. The efficiency of the chiral recognition property of D-mannose is demonstrated in estimating the enantiomeric excess of α -phenylethylamine.

Calcium Phosphate Phase Identification Using XPS and Time-of-Flight Cluster SIMS

Reproducible time-of-flight cluster static secondary ion mass spectra (ToF-SSIMS) were obtained for various standard calcium phosphate (CP) powders, which allowed for phase identification. X-ray diffraction was not able to detect signals from microscopic amounts of CP (∼15 mmol m(-)(2)). The phases studied were α-tricalcium phosphate [α-Ca(3)(PO(4))(2)], β-tricalcium phosphate [β-Ca(3)(PO(4))(2)], amorphous calcium phosphate [Ca(3)(PO(4))(2)·xH(2)O], octacalcium phosphate [Ca(8)H(2)(PO(4))(6)·H(2)O], brushite (CaHPO(4)·2H(2)O), and hydroxyapatite [Ca(10)(PO(4))(6)(OH)(2)]. The SIMS spectra were obtained via bombardment with (CsI)Cs(+) projectiles. X-ray photoelectron spectroscopy (XPS) core levels of the P 2p, Ca 2p, and O 1s orbitals and the relative O 1s loss intensity were examined. The PO(3)(-)/PO(2)(-) ratios from ToF-SSIMS spectra in conjunction with XPS of the CP powders showed much promise in differentiating between these phases at microscopic CP coverages on the metal oxide surface.

Differentiation of derivatized leucine and isoleucine by tandem mass spectrometry under liquid secondary ion mass spectral conditions

In the liquid secondary ion mass spectra of N-acetyl, N-benzoyl and N-pivaloyl leucine and isoleucine the relative abundance of [MH − (H2O,CO)]+ ions is greater in the case of N-substituted isoleucine. The difference is more distinctive in the collision-induced dissociation spectra of [M + H]+ ions. The [MH − COOH]+. ions from N-substituted leucine and isoleucine selectively decompose to give ions corresponding to the loss of isopropyl and ethyl radicals respectively. This selective decomposition can be used to estimate the percentage of leucine or isoleucine in a mixture. Peptides containing leucine or isoleucine as the N-terminus residue also give this characteristic fragmentation for the corresponding N-benzoyl derivatives. © 1998 John Wiley & Sons, Ltd.

Probing silicon substitution in molecular sieves by plasma desorption mass spectrometry

Plasma desorption was used to produce secondary ion mass spectra from samples of unsubstituted and substituted aluminum phosphate materials. The yield of fingerprint ions representative of silicon oxide solids indicates that the incorporation of silicon into the material during synthesis and following calcination occurs via the formation of silicon-rich islands. Complementary X-ray photoelectron data provide supporting evidence that the surface of the substituted aluminum phosphate material becomes silicon rich and phosphorus depleted. No changes in the unsubstituted and substituted material with respect to composition and phase were detected using powder X-ray diffraction.

Charge-remote fragmentation in dialkylaminostyryl dyes

Dialkylaminostyryl probes with two long alkyl chains were used to investigate the energetics of charge-remote fragmentation (CRF). These compounds provide high-quality liquid secondary ion (LSI) and electrospray ionization (ESI) mass spectra in which the intact cation predominates. The intact cation undergoes CRF in LSI but not in ESI, in which the cation is of lower internal energy. CRF is initiated in collision-induced dissociation (CID) and surface-induced dissociation (SID) for intact cations generated by either LSI or ESI. Single bond cleavage to lose one entire alkyl chain followed by CRF within the remaining alkyl chain seems to be the lowest energy CID and SID process. © 1998 John Wiley & Sons, Ltd.

Surface Mass Spectrometry of Biotinylated Self-Assembled Monolayers

Biotin and biotinylated self-assembled monolayers (SAMs) on gold have been investigated using time-of-flight secondary ion mass spectrometry, direct laser desorption, laser desorption with 193 nm photoionization of ion- and laser-desorbed species, and laser desorption with vacuum ultraviolet (VUV, 118 nm) photoionization. Our results indicate that direct laser desorption and laser desorption combined with 193 nm multiphoton ionization can detect a chromophoric molecule like biotin that is covalently bound to a SAM. However, secondary ion mass spectra were dominated by fragmentation, and ion desorption/193 nm photoionization detected no species related to biotin. The dominant features of the laser desorption/VUV mass spectra were neat and Au-complexed dimers of intact and fragmented biotinylated SAM molecules. Multiphoton and single-photon ionization of laser-desorbed neutrals from biotinylated SAMs both led to the production of ions useful for chemical analysis of the monolayer. Multiphoton ionization with ultraviolet radiation was experimentally less challenging but required a chromophore for ionization and resulted in significant fragmentation of the adsorbate. Single-photon ionization with VUV radiation was experimentally more challenging but did not require a chromophore and led to less fragmentation. X-ray photoelectron spectra indicated that the biotinylated SAM formed a disordered, 40-60 Å thick monolayer on Au. Additionally, projection photolithography with a Schwarzschild microscope was used to pattern the biotinylated SAM surface and laser desorption/photoionization was used to detect biotinylated adsorbates from the ∼10 μm sized pattern.

Ions Formed by Reaction between Solvent and Sample in the Liquid Secondary Ion Mass Spectra of Some Metal Acetylacetonates

Ions Formed by Reaction between Solvent and Sample in the Liquid Secondary Ion Mass Spectra of Some Metal Acetylacetonates

Characterization of supported and unsupported transition metal compounds by liquid secondary ion mass spectrometry

The positive ion liquid secondary ion mass spectra (LSIMS) of metal acetylacetonates (acacs) contain cluster ions that involve multiple metal centers. Several metal acacs form adduct ions with m-nitrobenzyl ( m-NBA) alcohol used as the LSIMS support matrix. In these adduct ions, deprotonated m-NBA molecules act as bridges between metal centers. The LSIMS of a series of dirhodium carboxylates show that the electron-withdrawing strength of the carboxylate group controls whether the base peak in the mass spectrum is the molecular ion or an adduct ion formed between the molecule and a matrix molecule of sulfolane. However, no cluster ions are formed for these dirhodium compounds. Similarly, highly charged cationic compounds do not form cluster ions, nor do they form adduct ions with the LSIMS solvent. Instead, the counter ion is retained to maintain a single positive charge in the ion. LSIMS spectra of neutral and charged metallocene compounds are compared. Contrary to the assertions that these compounds cluster extensively in the gas phase, the LSIMS provide no evidence for this process. To support studies of surfaces prepared for catalytic studies, silica- and clay-supported transition metal acacs were characterized by LSIMS. Release of the supported transition metal compounds from the surface occurs during ion exchange.