Metastable Ion Analysis Research Articles

Resonance Electron Attachment to Glucose and Fructose Molecules

Low-energy negative ion mass spectra of glucose and fructose suggest the deep fragmentation of short-lived molecular ions. An analysis of metastable ions in the mass spectra shows that some decomposition reactions proceed through intermediate [M–H2O]–, etc. ions. Along with the general similarity of the ionization processes in the isomers, there is a significant difference, which is in the intensive formation of m/z 71 ions from glucose.

Electron ionization (EI) mass spectra of exo-endo double-bond isomers of polycyano “push-pull” pentadienes derived from cycloalkylidene malonic acid derivatives

The title compounds, which exist in solutions as mixtures of exo/endo double bond isomers due to the “push-pull” effect of the electron-donating and electron-withdrawing substituents, were studied by mass-spectrometric methods. Their fragmentation routes under electron impact were established and confirmed by metastable ion analysis and accurate mass measurements. The results demonstrated that the relative amounts of exo/endo isomeric molecular ions are in close agreement with the isomeric ratios observed in solutions by the NMR, although the mass spectra of the tetracyano derivatives indicated a small fraction of molecular ions existing in the endo form, which could not be detected in solution by the NMR methods.

Electron ionisation mass spectral analysis and fragmentation pathways for some thiophosphorylic p-carboxybenzene sulfonamides.

The work presents the 70 eV electron impact mass spectra of some thiophosphorylic p-carboxybenzene sulfonamides, and proposes rationalisation of their fragmentation pathways. Accurate mass measurements of the fragment ions, and metastable ion analyses performed in the MIKES mode, were used to elucidate the most abundant ion compositions and to elucidate the fragmentation patterns of these pharmacologically interesting compounds.

Use of Cycloalkylcarbonyl Derivatives for the Determination of Amino Acid Methyl Esters by Gas Chromatography–Mass Spectrometry

Cycloalkylcarbonyl (cycloalkyl = cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl) derivatives were proposed for the determination of amino acid methyl esters by gas chromatography–mass spectrometry. These compounds are readily formed with the quantitative yield on heating hydrochlorides of amino acid methyl esters with cycloalkylcarbonyl chlorides. Although these derivatives exhibit lower chromatographic mobility than acetyl or perfluoroacyl derivatives, they form symmetric peaks. Mechanisms of the fragmentation of the new class of compounds under electron ionization conditions were studied in detail using high-resolution mass spectra and analysis of metastable ions. It was demonstrated that cyclopentylcarbonyl and cyclohexylcarbonyl derivatives can decompose with the cleavage of carbocycles.

Evidence for an aryl migration during the electron impact induced fragmentation of substituted aryloxymethylquinoxalines.

The electron impact (EI) mass spectra of 34 differently substituted 2-phenoxymethyl-, 2-naphthyloxymethyl-, 2-pyridinyloxymethyl- and 2-chinolinyloxymethylquinoxalines were recorded. The fragmentation patterns were examined by metastable ion analysis and exact mass measurements, employing finally also selective deuterium labelling. The inclusion of the substituted aryl ring moiety appears to be important for the fragmentation of the aryloxymethylquinoxalines. A molecular ion rearrangement is proposed for the observed loss of OH* and CHO* radicals. The influence of the different substituents on the aryl ring moiety on the rearrangement in the gas phase and on the resulting fragmentation was investigated.

Analysis of metastable decay by time-of-flight coincidence and kinetics energy measurements

A procedure for fragmentation pattern analysis of metastable ions, emitted in photon or ion induced desorption processes, is described. The method is based on a combination of three well-established techniques, namely: time-of-flight (TOF), coincidence counting, and electrostatic energy analysis in reflectron mass spectrometers. The key improvement comes from a judicious selection of the electrostatic mirror voltages for running the coincidence measurements in the best signal/noise conditions. The TOFs of stable species, as well as those of the neutral and ion fragments produced by all expected unimolecular-binary decays occurring in the field-free region before the mirror, are calculated and plotted as a function of the mirror voltage. The mirror voltages for coincidence measurements are selected after comparison of these dynamics plots of reflected and nonreflected species with experimental noncoincidence TOF spectra. To illustrate this procedure, the (LiF) nLi +∗ → (LiF) n−mLi + + (LiF) m 0 fragmentation pattern is analyzed.

Specific Electron Ionization-Induced Fragmentation of Secondary Alcohol Methoxyacetates

The electron ionization-induced fragmentations of methoxyacetates derived from various secondary aliphatic alcohols have been studied with the aid of deuteration experiments, high-resolution measurements and metastable ion analysis. It was shown that the formation of the methoxyacetic acid cation-radical or protonated methoxyacetic acid as well as α-cleavages near to the acyloxy group (processes which are characteristic for many esters) do not occur for these compounds. Unexpectedly, the elimination of methoxyacetic acid or the methoxyacetoxy radical from the molecular ions appeared to proceed to a nearly equal extent. The spectra of methoxyacetates of 2-, 3- and 4-alkanols contain peaks at m/z 89, 103 and 117 (and M −71), respectively, of a moderate intensity. Their origin was proved to be due to α-cleavages near to the methoxyacetoxy group followed by skeletal rearrangement and elimination of CO to form resonance-stabilized ions (R–CH=O+–CH2–O–CH3↔R–CH2–O+=CH–O–CH3).

Electronionization and chemical ionization mass spectrometric studies on 2-benzothiazolphenylhydrazones and 1-(2-benzothiazolyl)-3,5-diphenylformazans

The 70 eV electron ionization (EI) and chemical ionization (CI) mass spectra were recorded for six differently substituted 2-benzothiazolphenylhydrazones and five related 1-(2-benzothiazolyl)-3,5-di-­phenylformazans. The fragmentation patterns were studied by exact mass measurements, metastable ion analysis and collision-induced dissociation techniques. For both hydrazones and formazans the EI spectra were relatively simple, and especially for the formazans the dominance of the C3–N4 bond cleavage was striking. The CI spectra of the formazans were recorded with the use of ammonia, d3-ammonia, isobutane or methane as reagent gas. Only methane was used for the hydrazones because even it was able to cause only little fragmentation. In comparison with the hydrazones, the protonated formazans were relatively unstable, decomposing through several fragmentation pathways. Regardless of the reagent gas, the decomposition was always of the same degree and the spectra were closely similar. The most probable protonation site for the formazans was estimated by semiempirical calculations to be the benzothiazole nitrogen. This result is in agreement with the experimental data under both EI and CI, and showed that those tautomeric forms of formazans having a single bond between C3 and N4 are dominant in the gas phase. © 1998 John Wiley & Sons, Ltd.

Mass spectrometric fragmentation of 1-alkyl-5-bromo-4-hydroxypyridazin-6-ones under electron ionization conditions

The mass spectral fragmentation pathways of 1-alkyl-5-bromo-4-hydroxypyridazin-6-ones were studied under electron ionization by means of low resolution, high resolution and metastable ion analysis techniques. The principal fragmentation pathways of these compounds involved various skeletal rearrangements that involve transfer of hydrogen from the alkyl group to the carbonyl oxygen and to the N(1) and N(2) atoms. © 1998 John Wiley & Sons, Ltd.

Electron impact and multiphoton ionization at 351 nm, 248 nm and 193 nm of the dinuclear π-complexes: di-µ-carbonyl-biscyclopentadienyl-di-nickel, di-µ-carbonyl-dicarbonyl-biscyclopentadienyl-di-iron and di-µ-nitrosyl-bis(tetraisopropylcyclopentadienyl)-di-cobalt

Electron impact (EI) and nanosecond multiphoton ionization (MPI), at 351, 248 and 193 nm, of the title compounds, Cp2Ni2(CO)2 [1], Cp2Fe2(CO)4 [2] and (Cp-i4)2Co2(NO)2 [3], is reported (Cp = cyclopentadienyl; Cp-i4 = tetraisopropylcyclopentadienyl). Gas-phase formation enthalpies were derived for 1 and 2 and for some fragments. Fragmentation processes were identified by metastable ion analysis. EI ionization of 1 leads to molecular ions mainly decomposing by successive losses of the CO- and Cp- ligands. With MPI at 193 nm molecular ions are not detected and Cp2Ni2+ is the ion with the highest observed mass. At 248 and 351 nm only Ni+ appears. At 248 nm Ni+ is formed after absorption of four quanta. With 2, molecular ions, which decompose mainly by successive eliminations of the four CO- ligands, are formed under EI conditions. The resulting ions of composition Cp2Fe2(CO)n+ (n = 3–0) eliminate Fe and the Cp- ligands and finally yield Fe+. At 193 nm, molecular ions and Cp2Fe2(CO)3+ appear but only with low ...

Fragmentation of substituted pyrimido [6,1-a]isoquinolin-2-ones under electron ionization

The mass spectral fragmentations of eight substituted pyrimido[6,1-a]isoquinolin-2-ones and four pyrimido[6,1-a]isoquinoline-2,4-diones under electron ionization were examined by metastable ion analysis, a collision-induced dissociation technique and exact mass measurements. The major fragmentation pathways began as radical site-initiated cleavage, and ionization of the nitrogen atom in the isoquinoline ring seemed to prevail. Only the isoquinolinediones gave fragments resulting from ionization of the phenyl ring. Substitutents on N3 and C4 had larger effects on the peak intensities than substituents on C6. The major fragmentation pathway was different from that for the related oxazino [4,3-a]isoquinolines studied earlier. © 1997 John Wiley & Sons, Ltd.

Mass Spectrometric Study of α-Nitronyl Nitroxides. A Class of Stable Organic Radicals

The electron impact-induced fragmentation of α-nitronyl nitroxides has been studied by exact mass measurements, metastable ion analysis and collisional-induced dissociation. The formation of odd electron ions has been studied in detail in order to ascertain if they are a consequence of bimolecular reactions or an exception to the even-electron rule. © 1997 John Wiley & Sons, Ltd.

Mass Spectrometric Fragmentation of Saturated Isoindolobenzoxazepinones and -benzoxazinones Under Electron Ionization

The mass spectral fragmentation of three isoindolo[2,4]benzoxazepinones, five isoindolo[3,1]- and two isoindolo[1,3]benzoxazinones was studied under electron ionization by means of low-resolution, high resolution and metastable-ion analysis techniques. The major fragmentation pathways began as radical-site-initiated cleavage, and ionization of the nitrogen atom seemed to prevail. Ionization of the carbonyl and heterocyclic oxygen atoms was also observed. For the trinorbornene compound, a retro-Diels-Alder reaction was favoured.

Characterization of Stereoisomeric α-Methylene-γ-lactone Furanosidic Derivatives by Direct Chemical Ionization Mass Spectrometry and Liquid Secondary Ion Mass Spectrometry with Tandem Mass Spectrometry

Several furanosidic derivatives have been found to have biological activity and have been used both as fungicides and plant growth regulators. In particular, those carbohydrate derivatives that contain the α-methylene-γ-lactone unit have interesting potential applications. The present study deals with the mass spectrometric characterization of furanosidic compounds having a α-methylene-γ-lactone unit, using different ionization techniques: chemical ionization mass spectrometry and liquid secondary ion mass spectrometry together with metastable ion analysis and high-energy collision-induced dissociation. The objective of this study was to determine the influence on the respective fragmentation patterns of structural differences present in the stereoisomers. Common fragmentation differences relate to the extent of the loss of water which occurs together with the loss of acetone and to the formation of C7H7+ ions.

Characterization of Stereoisomeric α-Methylene-γ-lactone Furanosidic Derivatives by Direct Chemical Ionization Mass Spectrometry and Liquid Secondary Ion Mass Spectrometry with Tandem Mass Spectrometry

Several furanosidic derivatives have been found to have biological activity and have been used both as fungicides and plant growth regulators. In particular, those carbohydrate derivatives that contain the α-methylene-γ-lactone unit have interesting potential applications. The present study deals with the mass spectrometric characterization of furanosidic compounds having a α-methylene-γ-lactone unit, using different ionization techniques: chemical ionization mass spectrometry and liquid secondary ion mass spectrometry together with metastable ion analysis and high-energy collision-induced dissociation. The objective of this study was to determine the influence on the respective fragmentation patterns of structural differences present in the stereoisomers. Common fragmentation differences relate to the extent of the loss of water which occurs together with the loss of acetone and to the formation of C7H7+ ions.

Electron Impact Ionization‐induced Fragmentation of Uracil‐fused Tetrathiafulvalenes

The 70 eV electron ionization mass spectra of uracil-fused tetrathiafulvalenes have been studied by accurate mass measurement, metastable ion analysis and collision-induced dissociation. Changes in the structure of substituents, both in the tetrathiafulvalene moiety and on the N1 atom of uracil, cause important differences in the fragmentation scheme. The position of alkyl substituents in the uracil ring is unambiguously confirmed.

ＢＭＳ 扇形電場を用いたＴＯＦ質量分折計によるメタステーブルイオンの分析

A four sector time-of-flight (TOF) mass spectrometer has been constructed in order to improve mass resolution and ion transmission simultaneously. The multiple focusing (triple isochronous focusing and triple spacial focusing) conditions were achieved by using a symmetrical arrangement of four electrostatic sectors in a mass spectrometer. The principle of metastable ion analysis using the TOF mass spectrometer has been proposed and performed. Product ion spectra have been obtained by measuring the flight time and the kinetic energy of the products without any additional separation process, any coincidence technique or any special timing circuit. The sequential decays of a metal cluster ion have been observed in a MS/MS/MS analysis mode. The first-generation product ion has been produced by a metastable decay, and the second-generation product has been produced by a sequential decay in a flight.

Electron impact and multiphoton ionization and fragmentation of dicarbonyl cyclopentadienyl methyl iron and pentamethylcyclopentadienyl dicarbonyl methyl iron

Electron impact (EI) and multiphoton ionization (MPI) mass spectra of the title compounds CpFe(CO) 2CH 3 (1) and ∗CpFe(CO) 2CH 3 (2) are reported. Under EI molecular ions and large fragment ions are formed from both compounds. Direct analysis of metastable ions showed that successive detachments of ligands from 1 lead to Fe + ions while loss of Fe atoms is more important for ionic fragments of 2. Ionization energies of 7.56 eV (1) and 7.25 eV (2) were determined by extrapolating ion abundances versus energy in semi-log plots. In the same way, appearance energies of major fragment ions were obtained for both compounds. Derived data include ion dissociation energies and enthalpies of ion formation. Typically, the dissociation energies required were below 1 eV for splitting off CO ligands and above 2 eV for CH 3 detachment. Upon MPI of both compounds at the excimer wavelengths 351, 308 and 248 nm Fe + ions are formed almost exclusively, probably by breakdown of the neutral parent compounds yielding bare metal atoms that are subsequently ionized. At 193 nm, molecular ions appear and large fragment ions are generated with low abundance, depending on laser intensity. High laser intensities lead to complete breakdown and Fe + ion formation. At low intensities loss of Fe atoms is observed only in the case of 2. A dependence on pressure was observed for abundances of molecular ions and some fragment ions of 2. The abundances of C 10H 13 1 and of Fe + ions are independent of pressure.

Electron ionization mass spectra and crystal structures of some [1,2,4]triazolo[1,2‐b]‐ and [1,3,4]thiadiazolo[3,4‐b]phthalazines

AbstractThe mass spectra of ten 1,3‐dithioxo[1,2,4]triazolo[1,2,‐b]phthalazines, five 3‐iminosubstituted 1‐thioxo‐[1,3,4]thiadiazolo[3,4‐b]phthalazines, three 3‐iminosubstituted‐1‐thioxo[1,2,4]triazolo[1,2‐b]phthalazines, and 1,3‐dithioxo‐5,10‐dihydro[1,3,4]thiadiazolo[3,4‐b]phthalazine were recorded under electron ionization. The fragmentation pathways were elucidated by metastable ion analysis and exact mass measurements. The changes in the ring‐system had little effect on the fragmentation mechanism, but the effect on peak intensities was considerable. The most important fragmentations began with the opening of the triazole ring. Substituents at nitrogen atoms also had a marked effect on the mass spectral behavior. The aryl substituents prompted a whole new fragmentation. The X‐ray crystal structure was determined for a few compounds. Two of the three structures of the 1,3‐dithioxo[1,2,4]triazolo[1,2‐b]phthalazines that were studied proved to be relatively planar, whereas the structure of 1,3‐dithioxo‐5,10‐dihydro[1,3,4]thiadiazolo[3,4‐b]phthalazine was considerably bent similarly to the 2‐(4‐chlorophenyl)‐1,3‐dithioxo‐2,3,5,10‐tetrahydro[1,2,4]triazolo[1,2‐b]‐phthalazine. The triazole and the thiadiazole rings had a strong double bond nature.

Electron ionization mass spectrometry of some substituted, stereoisomeric, partly saturated 1,3‐ and 3,1‐benzoxazino‐1,3‐benzoxazines

AbstractThe electron ionization mass spectra of five substituted, partly saturated 3,1‐benzoxazino‐1,3‐benzoxazines and four substituted 1,3‐benzoxazino‐1,3‐benzoxazines were measured and analysed. The fragmentation pathways were elucidated by metastable ion analysis and exact mass measurement. Although the principal fragmentations were similar for all these compounds, there was an important difference between the two groups as concerns the fragmentation routes. Both routes led to the same fragment ion, but in different ways depending on the ring structure. On the basis of the different fragmentation mechanisms, the 3,1‐benzoxazino‐1,3‐benzoxazines and the 1,3‐benzoxazino‐1,3‐benzoxazines can be distinguished mass spectrometrically. The saturation, the stereochemistry and the substituents all affected the fragmentations, mainly the peak intensities.