Characterization of combinatorially designed polyarylates by time-of-flight secondary ion mass spectrometry

A series of 16 polyarylates, with well-controlled and systematically varying chemistry, has been characterized by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The polymers are structurally identical except for the incremental additions of C2H4 units to the backbone and sidechain. From the spectra, peaks characteristic of all polyarylates are identified. Furthermore, evaluation of the spectra and identification of unique signals allow classification of the polyarylates according to sidechain and backbone chemistry.     

Differentiation of positional isomers of nitro meso-tetraphenylporphyrins by tandem mass spectrometry

We studied by tandem mass spectrometry two isomers of nitro meso-tetraphenylporphyrin, one with a nitro group in the para position of a phenyl ring and the other with the same group in a beta-pyrrolic position, and their copper complexes. Collisional activation of the molecular ions of both free-base porphyrins and of their copper complexes produces an array of product ions that permit ready differentiation of the two positional isomers. The diagnostic ions, when the nitro group is in a beta-pyrrolic position, may be produced through intramolecular and double cyclization processes, triggered by the interaction of the nitro substituent with the neighboring meso-phenyl ring. These diagnostic ions do not form when the nitro group is in the para position. The gas-phase processes have precedents in solution chemistry.     

Characterization of polysiloxanes with different functional groups by time-of-flight secondary ion mass spectrometry

Polydimethylsiloxane (PDMS), polyhydromethylsiloxane (PHMS), and polymethylphenylsiloxane (PMPhS) have been studied by TOF-SIMS to investigate effects of functional group changes on polymer fragmentation mechanisms. Cyclic fragments are observed in the low mass range spectra of PDMS and PHMS, but not in the spectrum of PMPhS. Effects of functional group substitution on the fragmentation mechanisms of polysiloxanes are evident in the high mass range spectra (>1000 Da). Peaks of oligomers cationized by silver dominate the high mass range of the spectra of all low molecular weight polysiloxanes. However, fragmentation patterns of these samples are different. Neutral cyclic fragments cationized by silver are identified in the high mass range of the spectra of PDMS and PHMS, but not in the spectrum of PMPhS. The major fragments of PHMS and PMPhS are [oligomer-14+Ag]⁺. The PHMS spectrum also shows peaks [oligomer-28+Ag]⁺. These distinctive fragmentation patterns can be used to identify the polysiloxanes.     

Characterization of beam-induced reactions occurring in liquid secondary ion mass spectrometry/fast-atom bombardment by tandem mass spectrometry

Department of General and Physical Chemistry, University of Liege, Liege, Belgium A specific beam-induced secondary reaction involving the condensation of hydroxylic matrices with some organic groups (aldehydes, ketones, etc.) accompanied by the loss of a water molecule was investigated by liquid secondary ion mass spectrometry/fast-atom bombardment (LSIMS/FAB). A mechanistic scheme and a structure of the induced product are proposed. The features of this secondary reaction were studied and the influence of the types of solutes, acidic additives, and matrices analyzed. Rather than a drawback, LSIMS/FAB mass spectrometry can take advantage of this matrix effect to infer analytical information through tandem mass spectrometry experiments. Specific neutral loss scans can be conducted to highlight beam-induced reactive molecules, even when the detection of these species is prevented in normal scan spectra by other surface-active components.     

Depth profile measurement by secondary ion mass spectrometry

The possibilities of measuring depth profiles by secondary ion mass spectrometry are evaluated. The influence of different instrumental and experimental parameters on depth resolution in the profiles are studied: the effects of primary ion beam characteristics, reactive gas adsorption and mechanical aperturing in secondary ion extraction are discussed. Beam effects are studied from the point of view of surface damage. The effects of secondary processes, such as crater edge effects, element mixing, preferential sputtering, background signals, (residual) gas contamination and ion-induced topographical and compositional changes are studied for thin metal and binary materials.     

Characterization of high explosive particles using cluster secondary ion mass spectrometry

The use of secondary ion mass spectrometry (SIMS) for the detection and spatially resolved analysis of individual high explosive particles is described. A C(8) (-) carbon cluster primary ion beam was used in a commercial SIMS instrument to analyze samples of high explosives dispersed as particles on silicon substrates. In comparison with monatomic primary ion bombardment, the carbon cluster primary ion beam was found to greatly enhance characteristic secondary ion signals from the explosive compounds while causing minimal beam-induced degradation. The resistance of these compounds to degradation under ion bombardment allows explosive particles to be analyzed under high primary ion dose bombardment (dynamic SIMS) conditions, facilitating the rapid acquisition of spatially resolved molecular information. The use of cluster SIMS combined with computer control of the sample stage position allows for the automated identification and counting of explosive particle distributions on silicon surfaces. This will be useful for characterizing the efficiency of transfer of particulates in trace explosive detection portal collectors and/or swipes utilized for ion mobility spectrometry applications.     

Characterization of polymeric surfaces and interfaces using time-of-flight secondary ion mass spectrometry

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is used for chemical analysis of surfaces. ToF-SIMS is a powerful tool for polymer science because it detects a broad mass range with good mass resolution, thereby distinguishing between polymers that have similar elemental compositions and/or the same types of functional groups. Chemical labeling techniques that enhance contrast, such as deuterating or staining one constituent, are generally unnecessary. ToF-SIMS can generate both two-dimensional images and three-dimensional depth profiles, where each pixel in an image is associated with a complete mass spectrum. This Review begins by introducing the principles of ToF-SIMS measurements, including instrumentation, modes of operation, strategies for data analysis, and strengths/limitations when characterizing polymer surfaces. The sections that follow describe applications in polymer science that benefit from characterization by ToF-SIMS, including thin films and coatings, polymer blends, composites, and electronic materials. The examples selected for discussion showcase the three standard modes of operation (spectral analysis, imaging, and depth profiling) and highlight practical considerations that relate to experimental design and data processing. We conclude with brief comments about broader opportunities for ToF-SIMS in polymer science.     

Characterization of VX on concrete using ion trap secondary ionization mass spectrometry

The nerve agent VX (O-ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate) was analyzed on the surface of concrete samples using an ion trap secondary ion mass spectrometer (IT-SIMS). It was found that VX could be detected down to an absolute quantity of 5 ng on a concrete chip, or to a surface coverage of 0.0004 monolayers on crushed concrete. To achieve these levels of detection, the m/z 268-->128 ion fragmentation was measured using MS2, where m/z 268 corresponds to [VX + H]+, and 128 corresponds to a diisopropylvinylammonium isomer, that is formed by the elimination of the phosphonothiolate moiety. Detection at these levels was accomplished by analyzing samples that had been recently exposed to VX, i.e., within an hour. When the VX-exposed concrete samples were aged, the SIMS signature for intact VX had disappeared, which signaled the degradation of the compound on the concrete surface. The VX signature was replaced by ions which are interpreted in terms of VX degradation products, which appear to be somewhat long lived on the concrete surface. These compounds include ethylmethylphosphonic acid (EMPA), diisopropyl taurine (DIPT), diisopropylaminoethanethiol (DESH), bis(diisopropylaminoethane) disulfide [(DES)2], and a particularly tenacious compound that may correspond to diisopropylvinylamine (DIVA), or an isomer thereof. It was found that the thiolamine-derived degradation products DIPT, DESH, and (DES)2 were removed with isopropyl alcohol extraction. However, the DIVA-related degradation product was observed to strongly adhere to the concrete surface for longer than one week. Although quantitation was not possible in this set of experiments, the results clearly show the rapid degradation of VX on concrete, as well as the surface sensitivity of the IT-SIMS for intact VX and its adsorptive degradation products.     

Separation of glyceride positional isomers by silver ion chromatography

Separation of triglyceride and diglyceride positional isomers by silver ion high-performance liquid chromatography coupled with an evaporative light-scattering detector is described. The triglyceride isomers had a fatty acid composition of CLC and CCL, where C and L were caprylic acid and linoleic acid, respectively. Diglyceride isomers, 1,2(2,3)-diglyceride and 1,3-diglyceride, which contained caprylic acid were separated too. A solvent system based on n-hexane, 2-propanol, ethyl acetate, and acetonitrile with a flow-rate of 0.8 ml/min was developed. Calibration curves of CLC and CCL were achieved with triolein as internal standard. Using this method, the incorporation of linoleic acid onto specific a position of glycerol backbone can be monitored.     

Protein denaturation detected by time-of-flight secondary ion mass spectrometry

In the present work we investigate the denaturation of a functional protein, horseradish peroxidase (HRP), under various experimental conditions using time-of-flight secondary ion mass spectrometry. HRP was immobilized on TiO(2), and the samples were stored under different conditions. The activity of the enzyme was assessed colorimetrically and compared to ToF-SIMS spectra. We show that denaturation of the protein can be monitored using the ToF-SIMS signal of the disulfide bonds, which is related to the tertiary structure of the protein. As disulfide bonds appear in a vast range of proteins, the present findings may be of wide significance; i.e., a tool is provided that can allow the investigation of the presence of an active protein structure by a comparably simple surface analytical method.     

Characterization of an apolipoprotein C-III mutant by high-performance liquid chromatography and time-of-flight secondary ion mass spectrometry

Apolipoprotein (apo) C-III isoforms from a patient with a mutant apo C-III and from controls were isolated to homogeneity by isoelectric focusing and subjected to proteolytic digestion. The peptides obtained were separated by reversed-phase high-performance liquid chromatography, and their molecular masses were determined by time-of-flight secondary ion mass spectrometry. Molecular masses of peptides derived from apo C-III0, C-III1 and C-III2 were indistinguishable from control preparations, whereas the mutant apo C-III contained a COOH-terminal, carbohydrate-containing peptide with an abnormal retention time in high-performance liquid chromatography and a molecular mass higher by 291 daltons owing to oversialation at position 74 of the amino acid sequence (apo C-III3).     

Separation of fatty acids or methyl esters including positional and geometric isomers by alumina argentation thin-layer chromatography

This paper describes novel and rapid thin-layer chromatography procedures for the analysis of fatty acids and methyl esters using silver-impregnated alumina sheets. These techniques are known in most laboratories, and the equipment is readily available. The fatty acid method allows a separation of petroselinic (C18:1 delta 6c), oleic (C18:1 delta 9c), elaidic (C18:1 delta 9t), erucic (C22:1 delta 13c), and brassidic acids (C22:1 delta 13t), and the methyl ester method gives an excellent resolution with respect to the number, configuration, and position of the unsaturated centers. Sufficient separation for the subsequent ozonolysis and chromatographic quantification of isomeric C18 and C22 fatty acid methyl esters is obtained with both methods.     

Structural resolution of carbohydrate positional and structural isomers based on gas-phase ion mobility-mass spectrometry

This report describes the rapid characterization of positional and structural carbohydrate isomers based on structural separations provided by ion mobility-mass spectrometry (IM-MS). Many of the diseases associated with glycoprotein variation can be more effectively treated with earlier detection substantiating the need for high-throughput methodologies for glycan characterization. This remains particularly difficult due to heterogeneity, branching, and large size of carbohydrate moieties which creates the potential for numerous isobaric positional and structural isomers that are difficult to characterize using conventional MS methods. IM-MS provides rapid (μs to ms) structural separations by IM and subsequent identification by MS which presents a means for characterization of positional and structural carbohydrate isomers. To chart the structural variation observed in IM-MS, the ion-neutral collision cross sections for over 300 carbohydrates are reported. This diversity can also be varied through the utility of using different alkali metals to tune separation selectivity via alkali metal-carbohydrate coordination. Furthermore, the advantages of combining either pre- and/or post-IM fragmentation prior to MS analysis is demonstrated for enhanced confidence in carbohydrate identification.     

Quantitative analysis of microstructures by secondary ion mass spectrometry.

The focus of this review is on trace-element quantitation of microstructures in solids. This review is aimed at the nonspecialist who wants to know how secondary ion mass spectrometry (SIMS) quantitation is achieved. Despite 35 years of SIMS research and applications, SIMS quantitation remains a fundamentally empirical enterprise and is based on standards. The most used standards are "bulk standards"-solids with a homogeneous distribution of a trace element-and ion-implanted solids. The SIMS systematics of bulk standards and ion-implanted solids are reviewed.     

Surface analysis of polymer materials by secondary ion mass spectrometry

Atomic as well as molecular secondary ions are emitted from the uppermost monolayer of a solid during ion bombardment. Mass analysis of these positive and negative secondary ions supplies detailed information on the chemical composition of the bombarded surface. High mass range (> 10,000 u), high mass resolution (m/Δm > 10,000), accurate mass determination (ppm range) and high sensitivity (ppm of a monolayer) are achieved by applying time-of-flight (TOF) mass analyzers. TOF-SIMS has been successfully applied to a wide variety of polymer materials, including polymer blends, chemically or plasma modified surfaces, and plasma polymerization layers. Detailed information on the composition of repeat units, endgroups, oligomer distributions, additives, as well as surface contaminants can be obtained. Basic concepts of TOF-SIMS will be described and typical analytical examples for the characterization of polymer materials will be presented.     

Alpha spectrometry and secondary ion mass spectrometry of electrodeposited uranium films

Electrodeposited natural uranium films prepared by electrodeposition from solution of uranyl nitrate UO₂(NO₃)₂·6H₂O on stainless steel discs in electrodeposition cell. Solutions of NaHSO₄, and Na₂SO₄ and electric current from 0.50 up to 0.75 A were used in this study. Recalculated weights and surface’s weights of ²³⁸U from the alpha activities and secondary ion mass spectrometry (SIMS) intensities resulted in a linear regression. A dependency between of ²³⁸U surface’s weights recalculated from alpha activities and signal intensity of ²³⁸U in SIMS was investigated in order to determine a potential of SIMS in quantitative analysis of surface samples containing uranium. In the SIMS spectra of electrodeposited uranium films we found that upper layer consist not only from isotopes of uranium (ions ²³⁴U⁺, ²³⁵U⁺, and ²³⁸U⁺). In the positive polarity SIMS spectra, various molecules ions of uranium were suggested as UH⁺, UH₂ ⁺, UO⁺, UOH⁺, UO₂ ⁺, UO₂H⁺, UO₂H₂ ⁺, as well as possibly ions UNO⁺ and UNOH⁺.     

Quantitative analysis by thin-layer chromatography with secondary ion mass spectrometry

Summary A direct combination of thin-layer chromatography with secondary ion mass spectrometry (TLC/SIMS) provides a method for the quantitative analysis of thermally unstable compounds or compounds of low volatility such as nicergoline. The method is very simple and has excellent precision. The analysis was performed by using an aluminium TLC plate and a mixture of methylene chloride, acetone, and distilled water as a developing solvent. After development the portion of the plate with the nicergoline and the internal standard spots was cut off the TLC plate, and was attached to the SIMS holder directly. The amount of nicergoline was determined from the ratio of the fragment ion intensity of the nicergoline to the internal standard. The calibration curve was linear, and the detection limit was 10 ng at a signal-to-noise ratio of 5. This method should be considered for application to the determination of drugs in biological samples and also for the determination of possible impurities and decomposition products in drugs.     

Direct analysis of thin-layer chromatograms and electrophoretograms by secondary ion mass spectrometry

Mixtures separated by thin-layer chromatography and electrophoresis can be analyzed in situ by secondary ion mass spectrometry. The paramount advantage of such a combination is the selectivity inherent to the mass spectrum, which can provide information sufficient for the identification of an unknown compound as well as precise quantification of known compounds. Separation of the time frames of chromatographic development and mass spectrometer operation relaxes the constraints on each, and unique analytical advantages result.