Field Desorption Mass Research Articles

Development of a new electron ionization/field ionization ion source for gas chromatography/time‐of‐flight mass spectrometry

We have developed a combined EI/FI source for gas chromatography/orthogonal acceleration time-of-flight mass spectrometry (GC/oaTOFMS). In general, EI (electron ionization) and FI (field ionization) mass spectra are complementary: the EI mass spectrum contains information about fragment ions, while the FI mass spectrum contains information about molecular ions. Thus, the comparative study of EI and FI mass spectra is useful for GC/MS analyses. Unlike the conventional ion sources for FI and EI measurements, the newly developed source can be used for both measurements without breaking the ion source vacuum or changing the ion source. Therefore, the combined EI/FI source is more preferable than the conventional EI or FI ion source from the viewpoint of the reliability of measurements and facility of operation. Using the combined EI/FI source, the complementarity between EI and FI mass spectra is demonstrated experimentally with n-hexadecane (100 pg): characteristic fragment ions for the n-alkane such as m/z 43, 57, 71, and 85 are obtained in the EI mass spectrum, while only the parent peak of m/z 226 (M+) without any fragment ions is observed in the FI mass spectrum. Moreover, the field desorption (FD) measurement is also demonstrated with poly(ethylene glycol)s M600 (10 ng) and M1000 (15 ng). Signals of [M+H]+, [M+Na]+ and [M+K]+ are clearly detected in the FD mass spectra.

ガスクロマトグラフィー／飛行時間型質量分析法を用いた原油・石油製品のタイプ分析

Type analysis of crude oil and petroleum products has been studied using a gas chromatograph/time-of-flight mass spectrometer. The use of inert fused silica capillary tube inlet/field ionization (blank tube inlet/FI) is a suitable method for analyzing low boiling point components. Field ionization (FI) and field desorption (FD) methods are classified as soft ionization. Therefore, those ionization methods are used to analyze samples in which the molecular ion is hardly detected on electron ionization, as in the case of hydrocarbons. Type analysis using blank tube inlet/FI, capillary gas chromatography/FI (GC/FI), and FD mass spectra provides useful information, such as the average molecular weight. We examined the composition of crude oil and some petroleum products by type analysis using blank tube inlet/FI, capillary GC/FI, and FD. We carried out type analysis using six series of components. These were CnH2n+2, CnH2n, CnH2n-2, CnHn-4, CnHn-6, and CnHn-8. The averaged molecular weight by FD was much higher than that by blank tube inlet/FI, because it is difficult to measure low boiling point components by FD. In the blank tube inlet/FI method, all components were introduced and ionized. Therefore, this method is much more suitable than other methods for evaluating the composition of crude oil and petroleum products.

Molecular species composition of rat liver phospholipids by ESI-MS/MS: the effect of chromatography

Using electrospray ionization tandem mass spectrometry (ESI-MS/MS) this study shows that the loss of glycerophospholipid (GPL) after chromatography was unevenly distributed across the GPL molecular species. Both TLC and HPLC caused a preferential loss of GPL with 0 to 3 double bonds: 20% and 7.2% for choline glycerophosphates (PC) and 19.7% and 7.5% for ethanolamine glycerophosphates (PE), respectively. A consequence of these losses was that GPLs containing fatty acids with four or more double bonds had a greater contribution to the total after chromatography. ESI-MS/MS analysis also showed that PC molecular species with four or more double bonds migrated at the front of the TLC band of PCs. GPLs extracted from TLC plates occasionally contained PCs that were smaller than those in the original extract. These low molecular mass PCs were easily reduced to alcohols and formed derivatives with 2,4-dinitrophenylhydrazine, suggesting that aldehydes were generated by the oxidation of unsaturated fatty acids. Directly analyzing lipid extracts by ESI-MS/MS without preliminary chromatographic separation gives an accurate distribution of GPL molecular species in lipid mixtures. However, the ionization of the phospholipids in the electrospray jet maximized at relatively low concentrations of GPL. There was a linear response between phospholipid mass and ion intensity for concentrations around 1-2 nmol/ml for both PC and PE. The total ion intensity continued to increase with concentrations above 1-2 nmol/ml, but the response was non-linear.

Influence of Electric Field Strength and Emitter Temperature on Dehydrogenation and C—C Cleavage in Field Desorption Mass Spectrometry of Polyethylene Oligomers

The influence of electric field strength and emitter temperature on dehydrogenation and C–C cleavage in field desorption (FD) mass spectrometry of polyethylene (PE) oligomers of average molecular weights ranging from 500 to 2000 is examined. Low mass oligomers yield molecular weight (MW) distributions that are basically in accordance with results from gel-permeation chromatography. For these materials, dehydrogenation can be greatly reduced by reduction of the emitter potential. Furthermore, the influence of emitter potential on MW distributions indicates the occurrence of field-induced C–C cleavages. Reliable MW distributions are more difficult to obtain from higher mass oligomers by FD-MS because of the need for higher field strength and higher emitter temperatures to effect their desorption/ionization. Experiments reveal that the application of FD-MS to PE oligomers is limited not only by field-induced but also by thermally-induced fragmentations. Even then, FD mass spectra contain valuable information on mass range and homogeneity of PE samples up to about m/z 3600.

Mass spectra of aminoacyl adenylate pentacoordinated phosphorus compounds

Aminoacyl adenylate pentacoordinated phosphorus compounds were analyzed by field desorption (FD) and fast atom bombardment (FAB) mass spectrometries, together with the B/E linked scan technique, and their mass spectral fragmentation pathways were investigated. For the five bonds (one P-N bond, three P-O bonds and one mixed anhydride bond P-O-CO), the cleavage usually occurred more on the P-N bond, the mixed anhydride bond and the O-C bond adjacent to the P-O bond, and less on the P-O bond. Ion YH(+), corresponding to water loss from protonated 2',3'-O-isopropylidene-adenosine, was the base peak. The results reflect the structural characteristics of aminoacyl adenylate pentacoordinated phosphorus compounds. Copyright 1999 John Wiley & Sons, Ltd.

High-Pressure Synthesis of Cyclic Diphenylacetylene Oligomer.

New conjugated oligomers were synthesized by reacting diphenylacetylene at pressures of 0. 13 to 0. 76 GPa and at temperatures of 250 to 300°C for 1-10 h. The number-average molecular weight Mn and the weight-average molecular weight Mw, increased with pressure, but those values were independent of temperature and time (Mn:320-490, Mw:350-580). Elementary analysis, field desorption mass (FDMS) spectrometry, FTIR, and 13dC NMR experiments revealed that the oligomers above and including pentamer were new compounds having cyclic structures.

Characterization of Phospholipids by Electron Impact, Field Desorption and Liquid Secondary Ion Mass Spectrometry

Dimyristoylphosphatidylglycerol (DMPG), dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) were characterized by electron impact (EIMS), field desorption (FDMS) and liquid secondary ion (LSIMS) mass spectrometry. The results showed that the fragmentation processes of the three phospholipids are very similar. In the EI mass spectra, no molecule-ion peaks were found, the peaks of the fatty acid chains being dominant. The results of FDMS and LSIMS showed that both techniques worked particularly well with all three kinds of phospholipids. The FD mass spectra of all three phospholipid gave strong MH+ peaks, and no fragmental peaks were found except that of DMPC. With LSIMS, the fragmentations of all the phospholipids were extensive and clear, and gave dominant peaks of MH+. The cleavages around phosphate groups were the most abundant. An interesting phenomenon was found in the LSIMS measurements that all three kinds of phospholipids formed intense peaks of molecule-ion clusters, [2M+H]+, [3M+H]+ and [4M+H]+, etc. It was found that the formation of the molecule-ion clusters was related to several factors: concentration, ionic strength, pH, etc., among which concentration is the most important. The degree of cluster formation increased with increase in concentration of phospholipid. The results also showed that the nature of the matrix is critical to a successful LSIMS analysis of phospholipids, and (S)-glycerol was confirmed as a very satisfactory matrix for these phospholipids. © 1997 John Wiley & Sons, Ltd.

Ion-Pair Cationization Process in Liquid Secondary Ion Mass Spectrometry

Positive-ion fast atom bombardment (FAB) or liquid secondary ion mass spectra (LSIMS) typically provide the molecular mass of the organic sample M via the presence of a dominant protonated molecule (M+H)+ in the mass spectrum. In addition to the proton transfer reaction, cationization processes result in the formation of ions (M+Met)+, in which the metal is derived from metal salts present in the sample as impurities or purposefully added as promoters to the sample solution. Group I metal salts (lithium, sodium, and potassium salts are popular, but rubidium and cesium salts can also be used) result in cationized ions (M+Li)+, (M+Na)+, and (M+K)+. These ions provide multiple confirmations of the molecular mass M of the sample compound. Cationization reactions (as generalized Lewis acid/base reactions) are encountered not only in FAB and LSIMS but also in other desorption ionization methods of mass spectrometry, including field desorption (FD) mass spectrometry. Traditionally, cationization is considered to be the result of the addition of one singly charged metal ion to the neutral sample molecule. If the initial charge state of the metal ion is that of Met2+ or Met3+, the cationized form of the sample molecule observed in the mass spectrum is usually the singly charged species (M+Met)+, and an electron reduction must have occurred. For incorporation of two metal cations, there is always a concomitant loss of hydrogen to form, as an example, (M+2Met-H)+. Recent studies have re-examined the details of the cationization process. For instance, recent work has shown that when the organic sample molecule contains a nitro substituent, a cationization process can occur to form a singly charged ion that contains two alkali ions, viz., (M+2Met)+. The present work highlights yet another form of the cationization reaction.

High‐pressure synthesis of cyclic phenylacetylene oligomer

AbstractNew conjugated oligomers were prepared by reacting phenylacetylene under high pressure of 0.11 to 0.92 GPa at 100–200°C for 0–5 h. The number‐average molecular weight M̄n, the weight‐average molecular weight M̄w, and the oligomer yield increased with pressure, tem‐perature, and time. The average molecular weight of the oligomer showed the maximum value (M̄n: 830, M̄w: 2400) under 0.92 GPa, the maximum pressure, where phenylacetylene was oligomerized at a constant temperature. The structure of the oligomer was investigated from ESR, infrared, UV–VIS, field desorption mass (FDMS) spectra, and 13C NMR spec‐trum. Analysis of the FDMS spectrum revealed that the molecular weight of the oligomer was multiple of the monomer. 13C NMR spectrum of the oligomer showed the absence of sp‐carbon (C). We found that the oligomer had a cyclic structure. The cyclic oligomers of pentamer or more were new compounds. © 1995 John Wiley & Sons, Inc.

High-Pressure Synthesis of Polyacene-Based Oligomer

A new conjugated oligomer was synthesized by reacting diphenyldiacetylene under high pressure of 0.03-0.13 GPa at 250°C for 5 h. The oligomer was obtained from reacted diphenyldiacetylene in liquid state and of a molecular weight M n of 1200-1270 in polystyrene calibration. The fraction of the oligomer increased with increasing pressure. Visible absorption and IR spectra, field desorption mass (FDMS) spectrum, thin-layer chromatography, and 13 C NMR results indicate that the oligomer had a cyclic structure by the FDMS spectrum. The 13 C NMR spectrum for the oligomer corresponded to the polyacene-based structure. It was proposed that high-pressure oligomerization of diacetylene is a powerful method to produce a cyclic oligomer

Four‐sector tandem mass spectrometry: A comparison of the molecular and quasi‐molecular ions of the cyclic depsipeptide valinomycin formed using electron impact, chemical ionization, fast atom bombardment, field desorption and electrospray lonizatfion

AbstractFour‐sector tandem mass spectra of the molecular and quasi‐molecular ions of the cyclic depsipeptide valinomycin (RMM 1110.6) were compared. Electron impact (EI), chemical ionization (CI), fast atom bombardment (FAB), field desorption (FD) and electrospray ionization were used to create M+˙, [M + H]+, [M + Na]+ and [M + K]+ ions from valinomycin. Large differences were found between the FD and FAB tandem mass spectra of [M + Na]+ ions, and between the FD and EI tandem mass spectra of M+˙ ions. Differences between the spectra are ascribed to the formation of ions having the same mass but different structures. FAB tandem mass spectra of [M + Na]+ and [M + K]+ ions show greater degrees of fragmentation than do the FAB tandem mass spectra of [M +H]+ ions.

Synthesis of D-Glucopyranosyl Cholestan-3.BETA.-yl Glutamate Derivatives.

Preferential formation of 1-(cholestan-3β-yl) N-CBZ-L-glutamate (3) or 5-(cholestan-3β-yl) N-CBZ-L-glutamate (4) was obtained when dicyclohexylamine or 4-(dimethylamino)pyridine was used as a basic catalyst for ester formation, respectively. Each glutamate was converted to an anomeric mixture of glucose derivatives : 1-(cholestan-3β-yl) 5-(2, 3, 4, 6-tetra-O-benzyl-α- and -β-D-glucopyranosyl) N-CBZ-L-glutamates (7 and 8) or 5-(cholestan-3β-yl) 1-(2, 3, 4, 6-tetra-O-benzyl-α- and -β-D-glucopyranosyl) N-CBZ-L-glutamates (9 and 10), using 2, 3, 4, 6-tetra-O-benzyl-α-D-glucopyranose (11). After chromatographic separation of these isomers, their structures were determined by field desorption mass and nuclear magnetic resonance spectrometries.

Comparison of Peptide Fragmentation With Different Ionization Techniques: Variation With Sample Preparation Method of the Fragmentation of Luteinizing Hormone-Releasing Hormone Following Plasma Desorption

The fragmentation patterns of the peptide luteinizing hormone-releasing hormone (LH-RH) measured in plasma desorption mass spectrometry (PDMS) and keV-atom bombardment have been compared with the field desorption (FD) mass spectrum. Several different methods of preparing the samples for PDMS have been investigated, including application to a nitrocellulose surface which was preadsorbed with a protein. Similar fragment ions were observed in keV-atom bombardment and in PDMS applied to nitrocellulose which had not been preadsorbed with a protein; different fragment ions have been observed in FD mass spectrometry. The PDMS fragmentation when LH-RH was applied to nitrocellulose which had been preadsorbed with thioredoxin was found to differ yet again. The differences in the fragmentation are rationalized on the basis of differences in conformational constraints.

COMPARISON OF BARE WIRES AND ACTIVATED EMITTERS FOR FD MS OF OLIGOSACCHARIDES

Ion formation in field desorption (FD) from activated wire emitters covered with field enhancing microneedles has been compared with that from bare wires for some oligosaccharides doped with NaCl. The experiment revealed a close similarity between both types of emitters in the ion formation by electrohydrodynamic disintegration processes at temperatures near the onset of ion emission. In contrast, at higher temperatures above the melting point the sample layers are removed from smooth wires while on activated emitters they are retained in part between the microneedles. In this temperature range surface mobile molecules were found to be ionized not only by FI processes on microneedle tips but also by alkali ion attachment on charged alkali ion donating solid deposits. The latter mechanism has not been considered in FD mass spectrometry yet.

Investigation of field desorption mass spectral behaviour of prostaglandins for their determination in biological fluids.

Field desorption (FD) mass spectrometry was applied to the determination of prostaglandin E2 (PGE2) in urine. Studies on synthetic compounds showed that methyl esters are stable under FD mass spectrometric conditions. The ester of PGE2 gives rise to protonated molecular ions and fragments due to the elimination of water and the side chains C8H14O and C8H12O2. This behaviour enabled its determination in the nanogram per millilitre range.

Soft ionization techniques in mass spectrometry of distamycin and some analogues.

The results obtained using three different soft ionization techniques (field desorption (FD), fast atom bombardment (FAB) and desorption chemical ionization (DCI] on the antiviral antibiotic distamycin and on some analogues are reported. FAB mass spectra show more intense molecular ion and more regular fragmentation while FD and DCI mass spectra are dominated by thermally originated fragments. Information furnished by the three systems are different and complementary.

Thermal degradation of aliphatic polyamides studied by field ionization and field desorption mass spectrometry

AbstractThe aliphatic polyamides nylon 6.6, 6.9, 6.10, 6.12, 12.6, 12.10, and 12.12 of the diamine dicarboxylic acid‐type were pyrolyzed in the ion source of a double‐focusing mass spectrometer and the thermal degradation products were recorded by field ionization (FI) and field desorption (FD) mass spectrometry (MS). In the FI mode, several series of thermal degradation products differing in the number of polymer repeating units were detected up to 1000 Daltons. The main products were oligomers and, in addition, protonated dinitriles and various protonated nitriles are formed in large amounts except for nylon 6.6 and nylon 12.6. These two polymers form, in contrast to all other samples, large amounts of protonated amides and diamines. The technique employed allows distinction between oligomers already present in the original polymer and oligomers formed by thermal fission of bonds in the polymer chain. Reaction mechanisms are given that explain the products observed. High resolution experiments and accurate mass measurements were performed to confirm the proposed structures. In the FD mode, cationized oligomers (attached mostly to a sodium cation) were observed below 200°C with the dimers being the base peak for most samples. In contrast to the FI results, the monomers were only detected at very low intensities. Similarly, only weak signals for additional thermal degradation products were registered except for nylon 12.6. At higher temperatures the FD mass spectra gave protonated and doubly protonated oligomers in the high mass range up to 2000 Daltons, which resulted in complementary structural information about the polymers.

Chemical Structure of a New Modified Nucleoside Located in the Anticodon of Bombyx mori Glycine tRNA2

There are two species of glycine tRNA, tRNA(1Gly) and tRNA(2Gly), in the posterior silk glands of Bombyx mori. The first positions of their anticodons are guanosine and an unknown nucleoside for tRNA(1Gly) and tRNA(2Gly), respectively. This new nucleoside was isolated and the chemical structure was analyzed by thin layer chromatography and by UV, 1H-NMR, field desorption mass, and ORD spectroscopic measurements. The structure characterized by physical methods was finally confirmed by synthesis to be 5-((S)-carboxy(hydroxy) methyl)uridine methyl ester.

Possible occurrence of a β-carboline pathway in the oxidative catabolism of 5-hydroxytryptamine: Chemical approach and structure determination of a yellow substance and related β-carboline derivatives

The reaction of 5-hydroxytryptamine with severalfold excess silver oxide in a methanol medium at 65 to 70°C for several hours gave 6-hydroxy-3,4-dihydro-β-carboline ( I) as a main product. The yellow substance obtained in an aqueous system reported previously was identical to the latter compound with respect to NMR, field desorption (FD) mass spectroscopy, and other optical measurements. On the other hand, the same system in an ethanol medium gave 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-β-carboline ( II) as a main product. It became clear from the following results that silver oxide reacted with methanol to produce formaldehyde, and thereafter oxidized the adduct of 5-hydroxytryptamine with formaldehyde to produce the yellow substance. The borohydride-reduced yellow substance was determined to be 6-hydroxy-1,2,3,4-tetrahydro-β-carboline. Anaerobic incubation of 5-hydroxytryptamine with formaldehyde in ethanol did not give rise to the yellow substance. Upon the addition of silver oxide or the addition of iron-EDTA under air to this system, the yellow substance was found. The C-1 unit of formaldehyde was utilized, being incorporated into the yellow substance. Although iron-EDTA catalyzed the oxidative reaction, EDTA itself could also act as a C-1 unit donor to a minor extent. The most powerful donor of the C-1 unit of the yellow substance in our experiments was glyxylic acid. On aerobic oxidation of 5-hydroxytryptamine with glyoxylic acid, and more so together with iron-EDTA, the yellow substance was produced at a higher rate than with formaldehyde and iron-EDTA. Anaerobic incubation of 5-hydroxytryptamine with glyoxylic acid at 60°C at alkaline pH gave another yellow compound which was identified as 2-carboxymethyl-3,4-dihydro-β-carboline ( III), on the basis of NMR and FD mass spectrometry. The borohydride-reduced compound was found to be 6-hydroxy-2-carboxymethyl-1,2,3,4-tetrahydro-β-carboline. The reduced compound was hardly autoxidizable. A common precursor for both the yellow substance and the anaerobically formed yellow compound was isolated and purified from the anaerobic incubation mixture of 5-hydroxytryptamine and glyoxylate at alkaline pH. The structure was found to be 6-hydroxy-1-carboxyl-1,2,3,4-tetrahydro-β-carboline ( IV).

STRUCTURAL CHARACTERIZATION OF AROMATIC FRACTIONS OF SOME TYPICAL SOLVENT REFINED COALS USING MASS SPECTROMETRIC TECHNIQUES

ABSTRACT ABSTRACT Three aromatic fractions from two typical Chinese solvent-refined coals (one, FS2, derived from bituminous-sapropelitic cannel coal, and the other two, DT2A and DT2B, derived from a bituminous, weakly caking coal) were characterized for their chemical composition and molecular weight distribution using field ionization (FI) and field desorption (FD) mass spectrometric techniques. Some characteristic components derived from the chemical ionization technique were subjected to further fragmentation analyses using tandem mass spectrometry. The FS2 fraction is composed of 3-5 ring condensed aromatics of cata configuration with abundant naphthenic groups fused with an aromatic cluster. The most abundant component -- cyclopentachrysene -- is resolved at M/Z 268, which may possibly be the product of aroir.atization of hopanes existing in the source material during dia- and catagenesis. Sample DT2A contains polycyclic aromatic hydrocarbons with a higher degree of aromatic condensation and 3-5 rin...