Study of Gaseous Sample Ionization by Excited Particles Formed in Glow Discharge Using High-Resolution Orthogonal Acceleration Time-of-Flight Mass Spectrometer

The experimental results of a mass spectral analysis of volatile organic compounds in a gaseous sample, obtained using an original design of an ion source based on the Penning ionization of a gas sample by excited metastable inert gas atoms, are presented. Using ANSYS software, a gas-dynamic simulation of reagent gas flow from discharge zone to ionization region was carried out to analyze the effect of gas flow profile on the transport of metastable atoms and ionization efficiency. The n-octane and toluene samples diluted with helium at 100 ppb mole concentrations were used for our experiments. The resulting mass spectra of n-octane and toluene samples containe far more intensive molecular ions in comparison to n-octane and toluene electron ionization mass spectra from the NIST database. The sensitivity of 5 ions per 1 pg and 130 ions per 1 pg was achieved for n-octane and toluene molecular ions using the developed ion source combined with our mass spectrometer. The corresponding detection limits are 2.3 pg s^–1 for n-octane molecular ions and 0.08 pg s^–1 for toluene molecular ions. The detection limit for the reported ion source was considered theoretically.     

Ammonia chemical ionization mass spectra of esters and amides of oxyacids of phosphorus

Chemical ionization mass spectrometry using ammonia as the reagent gas has been carried out with esters and amides of a variety of oxyacids of phosphorus (phosphates, phosphonates, phosphites and phosphoramidates). In all cases, the protonated molecular ion is a major species in the spectrum and the percentage of the total ion current carried by these protonated molecular ions is always considerably greater than that carried by the molecular ions in the corresponding electron impact mass spectra. In the chemical ionization mass spectra only limited fragmentation of the protonated molecular ion occurs from which useful information on the structure of phosphorus derivatives may be inferred.     

Investigation of combwax of honeybees with high-temperature gas chromatography and high-temperature gas chromatography-chemical ionization mass spectrometry. II: High-temperature gas chromatography-chemical ionization mass spectrometry

Crude combwax of six various honey bee species have been analyzed by high-temperature gas chromatography (HTGC)-chemical ionization mass spectrometry after a two-step silylation procedure. An optimized chromatographic procedure, described previously, enables the separation of high-molecular mass lipid compounds resulting in a characteristic fingerprint of the combwaxes of different honeybee species. The coupling of HTGC to mass spectrometry requires appropriate instrumentation in order to achieve sufficient sensitivity at high elution temperatures and avoid loss of chromatographic resolution. Chemical ionization was carried out using methane as reagent gas in order to determine the molecular mass of the individual compounds by means of abundant quasi molecular ions. To confirm the presence of unsaturated wax esters, ammonia was used as reagent gas. More than 80 lipid constituents were separated and characterized by their mass spectra. Representative chemical ionization mass spectra of individual compounds are presented. Both, HTGC-flame ionization detection data and the results of the HTGC-mass spectrometric investigations enabled a rapid profiling of the individual classes of compounds in crude combwaxes.     

Stereochemical effects in mass spectrometry: 2—Chemical ionization mass spectra of some cyclic glycols and mono- and di-saccharides using trimethyl borate as reagent gas

The chemical ionization mass spectra of cyclic glycols and mono- and di-saccharides using trimethyl borate as reagent gas have been studied. In the gas phase, the trimethyl borate ions react stereospecifically with molecules of cis-cyclic glycols to form characteristic ions, from which the stereochemical isomers of 1,2-cyclopentanediols, 1,2-cyclohexanediols and mono- and di-saccharides can be definitely distinguished.     

Negative ion chemical ionization mass spectrometric studies of tetradentate schiff base coordination compounds. Fluorinecontaining reagent gases

Negative ion mass spectra using chemical ionization conditions have been measured for a series of tetradentate Schiff base corrdination compounds of Co(II), Ni(II) and Cu(II). Fluorine-containing reagent gases CF₄, SO₂F₂ and SF₆ have been used. The formation of molecular negative ions for the complexes is dependent on the reagent gas used. The secondary ions detected are produced by incorporation of CF₃, F and F₂ species into the coordination compounds.     

Application of negative chemical ionization mass spectrometry to the structure elucidation of perfluorochemicals and related compounds

The negative chemical ionization mass spectra of representative perfluorinated alkanes, cycloalkanes, ethers and tertiary amines have been examined, using Ar at about 0.5 torr as the reagent gas. The compounds chosen are typical of those under study as components of fluorochemical emulsion blood substitutes. Many such PFC's, particularly those with cyclic or branched structures, give intense molecular ions; most give simple spectra with a few major fragment ions at high mass, in marked contrast to the EI spectra which are dominated by m/e 69 (CF₃+) and 131 (C₃F₅+) of no value for structure elucidation. NCI-GC/MS is more sensitive than conventional EI-GC/MS and promises to be more generally useful for structure determination. Specific examples from the various classes will be presented, and their NCI and EI mass spectra compared.     

Stereochemical effects in mass spectrometry: Part 8-chemical ionization mass spectra of cyclic glycols and monosaccharides using formaldehyde dimethyl acetal as reagent gas

The chemical ionization mass spectra of cyclic glycols and monosaccharides using formaldehyde dimethyl acetal as reagent gas have been studied. In the gas phase, the stereospecific reaction of methylene acetal formation was observed. From the relative abundances of the characteristic ions the stereoisomers of these compounds may be definitely distinguished.     

The gas-phase amino–claisen rearrangement of protonated N-allylaniline

Metastable molecular protonated ions of N-allylaniline dissociate with significant losses of ethene and ammonia in the flight path of a mass spectrometer. The structures of the daughter ions formed on the loss of ethene have been elucidated using collision-induced dissociation and it is postulated that two isomeric structures are formed, one corresponding to molecular protonated ions which have undergone an amino–Claisen rearrangement. The relative proportion of this rearranged species is dependent on the exothermicity of the proton-transfer reaction between the sample molecule and the chemical ionization reagent gas ion. It is proposed that the two isomeric parent species differ in the site of protonation.     

Doubly charged ion mass spectra 8—alkenes

Doubly charged ion mass spectra of 23 alkenes have been measured using a double focusing Hitachi RMU-7L mass spectrometer. Ion mass spectra were obtained using 100 eV electron energy and 3.2 kV ion accelerating voltage. Each 2E spectrum was determined using the olefinic compound under investigation as the target gas. In general, spectra are dominated by fragment ions which result from extensive hydrogen loss from the doubly charged molecular ion. Appearnce energies have been measured for intense fragment ions in each spectrum.     

Bifunctional interaction and its effect on the esterification of dicarboxylic acids in chemical ionization mass spectrometry

The chemical ionization mass spectra of different dicarboxylic acids, including saturated and unsaturated aliphatic, aromatic, hydroxyl and amino-substituted dicarboxylic acids, have been studied using pure methanol as the reagent gas. Biomolecular monoesterification and diesterification product ions [M+15]⁺ and [M+29]⁺, and adduct ion [M+33]⁺, were observed, in addition to the protonated molecule [MH]⁺ and unimolecular water elimination product ions. The formation of a protonated molecule with bridged intramolecular hydrogen bond, and its effect on the esterification of dicarboxylic acids is discussed. Geometric isomers, such as maleic and fumaric acid, and ortho and meta isomers of phthalic acids can be distinguished from each other by methanol chemical ionization mass spectra. When ethanol was used as the reagent gas, similar mass spectra of some dicarboxylic acids were obtained.     

Chemical ionization mass spectrometry of halomethanes with tetramethylsilane as reagent gas

Chemical ionization mass spectra of halomethanes measured using tetramethylsilane as reagent gas exhibit three major peaks corresponding to [M + SiMe₃]⁺, [M − X]⁺ and (MeSi)₂X⁺ ions (X = Cl, Br or I). Dihalomethanes CH₂X₂ form the most stable silylated molecular ions, whereas in the mass spectra of tetrahalomethanes (CX₄) these ions have not been detected and the ions CX₃⁺ are the most abundant. Production of bistrimethylsilyl-halonium ions is the most pronounced process for haloforms (CHX₃).     

Chemical ionization and electron impact mass spectra of alicyclic substituted 2-aryl-1,3-dithianes

The methane and isobutane chemical ionization mass spectra of alicyclic substituted 2-aryl-1,3-dithianes were examined by gas chromatography mass spectrometry. The protonated molecular ion was found to be of low abundance in the methane spectra, while a protonated cyclic sulfide cation (m/z 107) appeared as the base peak. A protonated molecular ion was the base peak when isobutane was used as the reagent gas. Electron impact mass spectra displayed weak molecular ions and were characterized by the m/z 106 fragment.     

Skeletal rearrangements on chemical ionization of dibenzyl ether and derivatives

Protonated molecular ions of dibenzyl ether, formed by chemical ionization using hydrogen and isobutane as reagent gases, undergo skeletal rearrangements to lose water and formaldehyde, both in the ion source and the flight path. The rearrangements have been elucidated by deuterium labelling and chemical substitution. The water lost contains the reagent proton and an aromatic hydrogen atom, and the aromatic hydrogen atoms have been shown to be mobile prior to the reaction. It is proposed that the skeletal rearrangement for water loss is initiated by protonation on the ether oxygen atom, followed by benzyl migration. The formaldehyde lost contains benzylic hydrogen atoms exclusively, and it is proposed that the skeletal rearrangement is preceded by hydrogen rearrangement of an oxygen protonated molecular ion to a ring protonated molecular ion. Daughter ion structures are supported by comparisons of their collision induced dissociation spectra with those of isomeric ions prepared by alternative routes.     

Quantitative ion mobility spectroscopy based on molecular collision rate theory

Atmospheric pressure chemical ionization and ion mobility spectrometry (IMS) have traditionally been viewed as a qualitative analytical technique for identifying specific chemicals in the atmosphere. This work employs a nonlinear model based on molecular collision rate theory for quantitative modeling of chemical analyte concentrations. The collision rate between any two molecules depends on the relative populations of each chemical species in the volume of air analyzed where most collisions between ions, or neutral molecules and ions, result in no charge transfer. The rate constants for formation of product ions and consumption of source ions are estimated using empirical data over a wide concentration range for several analytes and reagent gases. The rate constants are unique to the analyte and the reagent gas as well as the sensitivity of the particular IMS instrument and provide a quantitative model to relate the mobility peak amplitudes to the analyte concentration. The rate constants can also be normalized by the reaction ion consumption rate constant to remove the IMS instrument sensitivity and provide a qualitative metric for analyte identification independent of a particular IMS instrument. A quantitative example is given for an acetic acid plume measured by a hand-held IMS detector outdoors has the plume passes. The quantitative rate constants provide a reasonable basis for estimating analyte concentration from the ion mobility spectra over a wide range of analyte concentrations.     

Structural elucidation of disinfection by-products in treated drinking water

Two unusual disinfection by-products have been detected periodically in the gas chromatography/mass spectrometry (GC/MS) characterization analyses of semi-volatile organics in treated drinking water. The electron ionization (EI) mass spectra contained mono-chlorinated and mono-brominated ions at m/z 107/109 and 151/153, respectively. Library searching techniques suggested mono-halogenated butanol structures but no matches could be found. Positive ion chemical ionization (CI) spectra contained mono-chlorinated and mono-brominated ions at m/z 105/107 and 149/151, respectively. No [M + H]+ ions were initially observed. Accurate mass measurements confirmed the empirical formulae for the significant ions in the EI spectra and the mono-halogenated butanol structures. Further CI experiments with other reagent gases and instruments revealed possible molecular weights of 139 and 183 Da, respectively. Tandem mass spectrometry (MS/MS) experiments in EI and CI were used to elucidate the fragmentation schemes. The two compounds have been tentatively identified as 1-aminoxy-1-chlorobutan-2-ol and 1-aminoxy-1-bromobutan-2-ol, respectively.     

Effect of Bleeding Oxygen on Processes in the Ion Source of an EMAL-2 Mass Spectrometer in the Analysis of Oxygen-Containing Samples

When bleeding oxygen into the ion source of an EMAL-2 laser mass spectrometer, an oxygen monolayer was formed on atomically pure sample surfaces produced by laser scanning. It was found that the signal of this oxygen can be used for calculating sensitivity factors. Bleeding oxygen increased the yield of test sample matrix ions; for example, the yield of Fe⁺ ions was doubled. The qualitative analysis of a gas atmosphere introduced into the ion source of an EMAL-2 mass spectrometer can be performed. Chloroform, which was present in a prepared gas mixture, was identified by the lines of molecular ions. The intensity of its molecular lines in the mass spectrum in the case using carbon reagent ions was higher by an order of magnitude than that in the case using silicon.     

A Chemical Ionization Mass Spectrometric Study of Fluorescamine and Fluorescamine - Amino Acid Derivatives

Abstract

The chemical ionization mass spectra of fluorescamine and fluorescamine - amino acid derivatives have been studied using methane and ammonia as reagent gases. Major ions in the spectra are protonated molecular ions, adduct ions and ions formed by loss of an oxygen atom.

Fluorescamine, 4-phenyl-spiro[furan-2(3H),1′-phthalan]3,3′-dione, is a powerful new fluorogenic reagent for assaying primary amines.¹ and EI² and EI³ mass spectrometric investigations of fluorescamine and its derivatives were carried out. Our present study reports the CI mass spectral analysis of fluorescamine and some of its amino acid derivatives.     

Chemical ionization mass spectrometry of derivatives of L-dopa and L-tryptophan and their detection in tumour samples

Conditions have been established for the detection by chemical ionization mass spectrometry (CIMS) of compounds related to L -dopa (3-hydroxy-L -tyrosine) and L -tryptophan without derivatization. The least fragmentation of the parent ion occurs in positive ion CIMS when methylamine is used as reagent gas. The compounds can also be detected by negative ion CIMS using carbon tetrachloride as reagent gas. While the total ion current in the latter technique is lower than that obtained with positive ion CIMS, the background noise in the mass spectra of samples obtained from natural sources is greatly reduced. CIMS has been used to show the presence of aromatic amino acids in acid extracts of samples of two different classes of tumour without sample derivatization.     

Chemical ionization mass spectrometry of dimethyl acetals and diethyl dithioacetals of aldopentoses and aldohexoses,and the influence of stereochemical configuration

Chemical ionization mass spectra have been recorded for the title compounds having the four pentose configurations and the eight hexose configurations, with ammonia and isobutane as the reagent gases. The ammonia mediated spectra display [NH₄]⁺ capture ions with successive loss of one or two molecules of methanol (acetals) or ethanethiol (dithioacetals), whereas when isobutane was the reagent gas, loss from the protonated acetals of one or two molecules of methanol and of water, and loss from the protonated dithioacetals of one or two molecules of ethanethiol and of water were featured. Significant differences in the ion intensities as a function of stereochemistry in the precursor are noted, and are discussed in terms of the ease of formation of cyclic fragment ions.     

Ammonia Chemical Ionization Mass Spectra of Sydnones

The mass spectra of twenty-nine sydnones were measured by using NII₃ as a reagent gas. The [M + H + NH₃]⁺ ions are the base peaks for the entire series. Very few fragment ions were observed except for the derivatives of 4-hydroxymethylenesydnones (XXI-XXIX). Only the relatively stable sydnonyl-methylene cations are formed. With consistent formation of [M + 18]⁺ ion as the base peaks with simple spectra, the NH₃ CI-MS can be an excellent method for the molecular weight determination.