Negative-ion Spectra Research Articles

Dicarboxylic acids analyzed by time-of-flight secondary ions mass spectrometry. Part II: Butanedioic acid

Time-of-flight secondary ion mass spectrometry was carried out to analyze a commercially available butanedioic acid (succinic acid) powder. Positive and negative polarity ion spectra were obtained using a 25 keV Bi3+ ion beam rastered over areas of 50 × 50 μm2. The main observed fragments were the protonated molecule [M+H]+ at 119 u and the deprotonated molecule [M-H]− at 117 u with their respective oligomers.

Dicarboxylic acids analyzed by time-of-flight secondary ions mass spectrometry. Part I: Propanedioic acid

Time-of-flight secondary ion mass spectrometry was carried out to analyze a commercially available propanedioic acid (malonic acid) powder. Positive and negative polarity ion spectra were obtained using a 25 keV Bi3+ ion beam rastered over areas of 50 × 50 μm2. The main observed fragments were the protonated molecule [M+H]+ at 105 Da and the deprotonated molecule [M-H]– at 103 Da with their respective oligomers.

Dicarboxylic acids analyzed by time-of-flight secondary ion mass spectrometry. Part 0: Ethanedioic acid

Time-of-flight secondary ion mass spectrometry was carried out to analyze a commercially available ethanedioic acid (oxalic acid) powder. Positive and negative polarity ion spectra were obtained using a 25 keV Bi3+ ion beam rastered over areas of 50 × 50 μm2. The main observed ions were the protonated molecule [M+H]+ at 91 Da and the deprotonated molecule [M-H]− at 89 Da with their respective oligomers.

Analysis of ToF‐SIMS spectra of poly(2‐vinylpyridine) and poly(4‐vinylpyridine) with density functional theory calculations

The time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) positive and negative ion spectra of poly(2‐vinylpyridine) (P2VP) and poly(4‐vinylpyridine) (P4VP) were analyzed using density functional theory calculations. Most of the ions from these structural isomers shared the same accurate mass, but had different relative abundance. This could be attributed to the fact that from a thermodynamics perspective, the disparity in the molecular structures can affect the ion stability if we assume that they shared the same mechanistic pathway of formation with similar reaction kinetics. The molecular structures of these ions were assigned, and their stability was evaluated based on calculations using the Kohn‐Sham density functional theory with Becke's 3‐parameter Lee‐Yang‐Parr exchange‐correlation functional and a correlation‐consistent, polarized, valence, double‐zeta basis set for cations and the same basis set with a triple‐zeta for anions. The computational results agreed with the experimental observations that the nitrogen‐containing cations such as C5H4N+ (m/z = 78), C8H7N+· (m/z = 117), C8H8N+ (m/z = 118), C9H8N+ (m/z = 130), C13H11N2+ (m/z = 195), C14H13N2+ (m/z = 209), C15H15N2+ (m/z = 223), and C21H22N3+ (m/z = 316) ions were more favorably formed in P2VP than in P4VP due to higher ion stability because the calculated total energies of these cations were more negative when the nitrogen was situated at the ortho position. Nevertheless, our assumption was invalid in the formation of positive ions such as C6H7N+˙ (m/z = 93) and C8H10N+ (m/z = 120). Their formation did not necessarily depend on the ion stability. Instead, the transition state chemistry and the matrix effect both played a role. In the negative ion spectra, we found that nitrogen‐containing anions such as C5H4N− (m/z = 78), C6H6N− (m/z = 92), C7H6N− (m/z = 104), C8H6N− (m/z = 116), C9H10N− (m/z = 132), C13H11N2− (m/z = 195), and C14H13N2− (m/z = 209) ions were more favorably formed in P4VP, which is in line with our computational results without exception. We speculate that whether anions would form from P2VP and P4VP is more dependent on the stability of the ions.

Analysis of mixed nitric oxide–water clusters by complementary ionization methods

Mixed clusters of nitric oxide and water are investigated by mass spectrometry using different ionization methods, namely (1) the electron ionization at 70eV (EI); (2) the doping with sodium atoms and subsequent photoionization (NaPI); and (3) the low energy electron attachment (EA). All these methods applied to the same molecular beam generated by mixed NO–water expansion yield distinctly different mass spectra. The EI spectra are dominated by the protonated water (H2O)nH+ ions, nevertheless, they show some evidence for the mixed NO–water clusters. The NaPI spectra exhibit only (H2O)n·Na+ ions which originate from the pure water clusters (H2O)N. The abundance of the pure water clusters generated in the mixed expansions is small compared to the abundance of the mixed species. The negative EA spectra clearly demonstrate the dominance of the mixed clusters, namely (H2O)n·NO2− and (H2O)n·(NO)m−, m=2, 3. None of the above mentioned methods alone can reveal the neutral cluster composition and size, however, based on their unique combination in our experiment, we can discuss the neutral clusters and ionization processes. In addition, we have investigated the negative ion intracluster chemistry by the theoretical calculations. Energetically favorable pathways from the (NO)3− ionic core to the NO2− in the presence of water are identified, justifying the generation of the (H2O)n·NO2− series. Further series in the negative ion spectra are discussed.

Time‐of‐flight secondary ion mass spectrometry of wet and dry chemically treated display glass surfaces

AbstractDisplay glasses meet the demands of the flat panel display industry vis‐à‐vis their composition, flatness, and forming processes. Here, we report the high‐resolution time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) characterization of Corning® EAGLE XG®, a widely used display glass, and subsequent chemometric analyses of these data. Samples analyzed included the as‐formed glass, fracture surfaces from remelt bars, and as‐formed surfaces subsequently exposed to process‐relevant treatments, including strong acids and bases, two industrial detergents, and an atmospheric‐pressure plasma treatment. Elemental signals in the positive ion ToF‐SIMS spectra respond to surface treatments. Acidic conditions leach non‐silica components from the surfaces, while basic treatments extract these species less efficiently. The detergents leave residues of Na+ and K+. The atmospheric pressure (AP) plasma treatment had little effect on the surface composition, while the melt surface differs significantly from the bulk fracture surface. Above ca. 75 m/z, the negative ion spectra are dominated by two series of homologous cluster ions with compositions of SinO2n+2Al− and SimHO2m+1H−. The presence of these clusters suggests that analogous structures exist at the near surface regions of the samples. In a series of multivariate curve resolution (MCR) analyses, two or three MCR components captured >95% of the variance in the data for these samples.

Secondary Ion Mass Spectrometry Analysis of Renal Cell Carcinoma with Electrospray Droplet Ion Beams.

Tissue samples from renal cell carcinoma patients were analyzed by electrospray droplet ion beam-induced secondary ion mass spectrometry (EDI/SIMS). Positively- and negatively-charged secondary ions were measured for the cancerous and noncancerous regions of the tissue samples. Although specific cancerous species could not be found in both the positive and negative secondary ion spectra, the spectra of the cancerous and noncancerous tissues presented different trends. For instance, in the m/z range of 500–800 of the positive secondary ion spectra for the cancerous tissues, the intensities for several m/z values were lower than those of the m/z+2 peaks (indicating one double bond loss for the species), whereas, for the noncancerous tissues, the inverse trend was obtained. The tandem mass spectrometry (MS/MS) was also performed on the tissue samples using probe electrospray ionization (PESI), and some molecular ions produced by PESI were found to be fragmented into the ions observed in EDI/SIMS analysis. When the positive secondary ion spectra produced by EDI/SIMS were analyzed by principal component analysis, the results for cancerous and noncancerous tissues were separated. The EDI/SIMS method can be applied to distinguish between a cancerous and a noncancerous area with high probability.

Ultraperformance convergence chromatography-high resolution tandem mass spectrometry for lipid biomarker profiling and identification.

Lipids represent biologically ubiquitous and highly dynamic molecules in terms of abundance and structural diversity. Whereas the potential for lipids to inform on disease/injury is promising, their unique characteristics make detection and identification of lipids from biological samples analytically demanding. We report the use of ultraperformance convergence chromatography (UPC2 ), a variant of supercritical fluid chromatography, coupled to high-resolution, data-independent tandem mass spectrometry for characterization of total lipid extracts from mouse lung tissue. The UPC2 platform resulted in lipid class separation and when combined with orthogonal column chemistries yielded chromatographic separation of intra-class species based on acyl chain hydrophobicity. Moreover, the combined approach of using UPC2 with orthogonal column chemistries, accurate mass measurements, time-aligned low- and high-collision energy total ion chromatograms, and positive and negative ion mode product ion spectra correlation allowed for confident lipid identification. Of great interest was the identification of differentially expressed ceramides that were elevated 24 h post whole thorax lung irradiation. The identification of lipids that were elevated 24 h post-irradiation signifies a unique opportunity to investigate early mechanisms of action prior to the onset of clinical symptoms in the whole thorax lung irradiation mouse model.

The Field Of Lyman-Alpha Radiation plus Current Sheets and Physics of Different Zones of the Solar Atmosphere

The solution of the problem of the Lyman-alpha radiation field in the solar atmosphere simultaneously with discovery of the current sheets (CS) in the Nature (on the Sun) have allowed by the author to revise both the available models of solar atmosphere and the nature of the corona. We distinguish four zones now in the external solar atmosphere, in their sequence and in their physical sense: photosphere, transition zone, chromosphere, and corona. Now, it is believed that coronal plasma temperature has exceeded of million degrees. Our results indicate the structure of the corona composed of multiple non-thermal jets of the CS that change the very notion of the term of temperature. The corona is transparent in all hydrogen lines of the Lyman series (the A case of Menzel approximation) and radiative processes take only place in excitation of hydrogen plasma. In the solar atmosphere physical conditions of any of zones are determined, in other equal conditions, by the hydrogen plasma density only. The corona begins when the density of plasma will decreased to nH 10 18 cm -3 , the continuous spectrum of the Sun arises, which is the radiation spectrum of negative hydrogen ions. In a vertical current sheet, the plasma density gradient causes a sharp decrease in the thickness of the compressed CS layer up to zero to the its middle and it turns the CS into the piston with one-sided eject up of the plasma. Multiple set of such accelerated plasma flows up and provides seemingly heat of the corona.

Travelling-wave ion mobility and negative ion fragmentation of high-mannose N-glycans.

The isomeric structure of high-mannose N-glycans can significantly impact biological recognition events. Here, the utility of travelling-wave ion mobility mass spectrometry for isomer separation of high-mannose N-glycans is investigated. Negative ion fragmentation using collision-induced dissociation gave more informative spectra than positive ion spectra with mass-different fragment ions characterizing many of the isomers. Isomer separation by ion mobility in both ionization modes was generally limited, with the arrival time distributions (ATD) often showing little sign of isomers. However, isomers could be partially resolved by plotting extracted fragment ATDs of the diagnostic fragment ions from the negative ion spectra, and the fragmentation spectra of the isomers could be extracted by using ions from limited areas of the ATD peak. In some cases, asymmetric ATDs were observed, but no isomers could be detected by fragmentation. In these cases, it was assumed that conformers or anomers were being separated. Collision cross sections of the isomers in positive and negative fragmentation mode were estimated from travelling-wave ion mobility mass spectrometry data using dextran glycans as calibrant. More complete collision cross section data were achieved in negative ion mode by utilizing the diagnostic fragment ions. Examples of isomer separations are shown for N-glycans released from the well-characterized glycoproteins chicken ovalbumin, porcine thyroglobulin and gp120 from the human immunodeficiency virus. In addition to the cross-sectional data, details of the negative ion collision-induced dissociation spectra of all resolved isomers are discussed.

Photochemical Reactions of Aminonaphthols Caused by Laser Desorption/Ionization.

The formation of monomeric and dimeric ions of seven different aminonaphthols (ANLs) has been studied by using laser desorption/ionization (LDI) with a nitrogen laser. The positive-ion data of all the ANLs merely showed molecular ion M(·+) without protonated molecule [M+H](+), while 1-amino-2-naphthol (1,2-ANL) and 2-amino-1-naphthol (2,1-ANL) showed an intense dimeric ion [2 M-2H2O+H](+). The negative-ion data showed deprotonated molecule [M-H](-) in common, while the spectra of 1,2-ANL, 2,1-ANL and 8-amino-2-naphthol (8,2-ANL) accompanied an intense peak corresponding to negative molecular ion M(·-) and the 8,2-ANL and 4-amino-1-naphthol (4,1-ANL) accompanied dehydrogenated anion [M-2H](·-). The formation of monomeric ions was discussed from the standpoints of thermochemical properties such as ionization energy, gas-phase acidity, electron affinity, and bond dissociation energy. The formation of dimeric ions [2 M-2H2O+H](+) observed in the 1,2-ANL and 2,1-ANL could be explained by the radical combination in the amino groups. An isomer 5-amino-1-naphthol (1-ANL) did not give any dimeric ions in the both positive- and negative-ion spectra. The influence of laser fluence upon the appearance of the monomeric ions such as M(·+), [M+H](+), [M-H](-) and [M-2H](·-) of the 5,1-ANL has been examined.

Detergent decellularization methods affect the surface molecular functionality of biologic scaffolds

Detergent decellularization methods affect the surface molecular functionality of biologic scaffolds

Thermally annealed iron thin film on an alumina barrier layer by ToF-SIMS

The authors report the positive and negative ion time-of-flight secondary ion mass spectrometry spectra obtained with Bi32+ primary ions at 50 keV of an Fe film annealed in hydrogen at 750 °C to form Fe nanoparticles. This surface had been exposed to the air; it had previously been shown by x-ray photoemission spectroscopy to be entirely oxidized. The strongest signal in the positive ion spectrum corresponded to Fe+, with FexOyHz+ species also present. A substantial Al+ signal was observed due to exposure of the underlying alumina substrate. The negative ion spectrum showed O−, OH−, and AlO−.

Thermally evaporated (oxide) iron on an alumina barrier layer by ToF-SIMS

The authors report the positive and negative ion time-of-flight secondary ion mass spectrometry spectra using Bi32+ primary ions at 50 keV of an Fe film (6 nm) that had been thermally evaporated on a thin film of alumina (ca. 35 nm) on a silicon wafer. This surface had been exposed to the air; it had previously been shown by x-ray photoemission spectroscopy (XPS) to be entirely oxidized. The positive ion secondary ion mass spectrometry spectrum shows Fe+, FeH+, and FexOyHz+ species. The negative ion spectrum shows FeOH−, FexOyHz−, and OH− species.

Al2O3 e-beam evaporated onto silicon (100)/SiO2 by ToF-SIMS

The authors report the positive and negative ion time-of-flight secondary ion mass spectrometry characterization of a thin film of e-beam evaporated alumina on a silicon substrate using Bi3++ primary ions at 50 keV, where this film prevents poisoning of a Fe catalyst in carbon nanotube growth. The positive ion spectrum showed a strong Al+ signal, while the negative ion spectrum showed strong peaks due to AlO−, AlO2−, AlO3H2−, and OH−.

Silicon (100)/SiO2 by ToF-SIMS

The authors report the time-of-flight secondary ion mass spectrometry of Si (100)/SiO2. Both positive and negative ion spectra were obtained using a cluster ion source (Bi32+ primary ions at 50 keV). Si+ is the base peak in positive ion mode. The negative ion spectrum shows signals characteristic of the native oxide: SiO2−, SiO2H−, SiO3−, and SiO3H−.

High-resolution electrospray mass spectra of hexaethylene glycol connected biotinylated HNK-1 antigenic trisaccharide molecular probe and its non-sulfated analogue

High-resolution electrospray mass spectra in positive and negative ion modes (MS and MS/MS) were measured and described for biotinylated hexaethylene glycol (HEG) connected molecular probes bearing HNK-1 (abbreviation of human natural killer cell-1 epitope) antigenic trisaccharide (1) and its non-sulfated analogue (2). For molecular probe 2, in its CID MS/MS of [M+2Na]2+, unexpected peak at m/z 530.2475 [C22H41N3O8SNa]+ was observed and attributed to the fragmentation of the aglycone at the end of the HEG chain distant from the biotin fragment. No homologous ions having the difference C2H4O smaller than that one were observed. The same cleavage was revealed in negative ion spectra. A similar fragmentation was found for other non-sulfated, biotinylated HEG-spacered molecular probes thus demonstrates this type of fragmentation characteristic for such glycosides.

Iron Fluoroanions and Their Clusters by Electrospray Ionization of a Fluorinating Ionic Liquid.

Metal fluoroanions are of significant interest for fundamental structure and reactivity studies and for making isotope ratio measurements that are free from isobaric overlap. Iron fluoroanions [FeF(4)](-) and [FeF(3)](-) were generated by electrospray ionization of solutions of Fe(III) and Fe(II) with the fluorinating ionic liquid 1-ethyl-3-methylimidazolium fluorohydrogenate [EMIm](+)[F(HF)(2.3)](-). Solutions containing Fe(III) salts produce predominately uncomplexed [FeF(4)](-) in the negative ion spectrum, as do solutions containing salts of Fe(II). This behavior contrasts with that of solutions of FeCl(3) and FeCl(2) (without [EMIm](+)[F(HF)(2.3)](-)) that preserve the solution-phase oxidation state by producing the gas-phase halide complexes [FeCl(4)](-) and [FeCl(3)](-), respectively. Thus, the electrospray-[EMIm](+)[F(HF)(2.3)](-) process is oxidative with respect to Fe(II). The positive ion spectra of Fe with [EMIm](+)[F(HF)(2.3)](-) displays cluster ions having the general formula [EMIm](+) (n+1)[FeF(4)](-) n, and DFT calculations predict stable complexes, both of which substantiate the conclusion that [FeF(4)](-) is present in solution stabilized by the imidazolium cation. The negative ion ESI mass spectrum of the Fe-ionic liquid solution has a very low background in the region of the [FeF(4)](-) complex, and isotope ratios measured for both [FeF(4)](-) and adventitious [SiF(5)](-) produced values in close agreement with theoretical values; this suggests that very wide isotope ratio measurements should be attainable with good accuracy and precision when the ion formation scheme is implemented on a dedicated isotope ratio mass spectrometer.

Experimental simulation of negative ion chemistry in Martian atmosphere using ion mobility spectrometry-mass spectrometry

We have studied the formation of negative ions in a negative Corona Discharge (CD) fed by CO2/N2 mixtures (with 0, 2, 4, 6, 8, 10% N2) using the technique of ion mobility spectrometry-orthogonal acceleration time of flight mass spectrometry (IMS-oaTOF). The composition of the negative ions was found to be dependent on the initial gas composition, the gas flow regime, the concentrations of neutral reactive species formed in the discharge and the trace amounts on water in the gases were found to play an important role in the negative ions formation. In a pure CO2 discharge operating under standard gas flow conditions of IMS (associated with strong interaction of ions with neutral reactive species formed in discharge) the ions CO3− (H2O) and CO4−(H2O) dominated the measured negative ion spectrum while in CO2/N2 mixtures NO3−(H2O)n, NO3−(HNO3) (n = 0, 1) ions prevailed. In the case of reverse gas flow regime (low interaction of ions with neutral reactive species formed in discharge), the negative ions detected were O2−(H2O)n, and O2−.CO2(H2O)n both in pure CO2 and N2/CO2 mixtures. The spectra of negative ions recorded for a gas mixture containing 4% N2 in CO2 were compared with theoretical predictions of negative ion composition in the lower atmosphere of Mars.

Detection of sialylated N-Linked glycans by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Native and methyl-esterified sialylated glycans were analyzed with 2, 4, 6-trihydroxyacetophenone (THAP) and 2, 5-dihydroxybenzoic acid (DHB) as matrix by a matrix-assisted laser desorption/ionization time-of-flight mass spectrometer (MALDI-TOF MS). High quality negative-ion spectra of commercial sialylated glycan were obtained with THAP as matrix. Detection limit of the glycan was less than 0.1 pmol. After methyl esterification of sialic acid (SA) residue, sialylated glycans were detected sensitively in the positive-ion mode using DHB as matrix. Neutral and sialylated glycans from the mixture of asialofetuin and fetuin were methylesterified and simultaneously recognized in one manipulation. Methyl esterification of SA residue offers a convenient and sensitive way to identify the structure of N-linked glycans for glycan profiling.