Chemical ionization mass spectrometry with amines as reactant gases. I—amine chemical ionization mass spectrometry of flavonoid aglycones

Chemical ionization mass spectrometry of 34 flavones, isoflavones, flavanones, chalcones and aurones with aliphatic amines and ammonia as reactant gases have been investigated. Some unusual ions have been obtained and are discussed. This method can be used to determine the type of flavonoid and the location of some functional groups in the molecule.     

Chemical ionization mass spectrometry with amines as reactant gases. V—Amine chemical ionization mass spectrometry of flavonoid glycosides

The chemical ionization mass spectra of flavonoid glycosides (O-glycosides, C-glycosides and acetylated glycosides) have been investigated. Triethylamine, ethylenediamine, diethylamine, methylamine and ammonia were used as reactant gases. The fragmentation mechanism is discussed, and the perspectives for establishing the molecular weights of glycosides, aid the nature of both the sugar residue and the aglycone, are outlined.     

Chemical ionization mass spectrometry with amines as reactant gases. VII—Amine chemical ionization mass spectrometry of some iridoid and secoiridoid glucosides

The chemical ionization mass spectra of iridoid glucosides of the loganin type and secoiridoid glucosides of the gentiopicroside type were investigated. Triethylamine, diethylamine, ethylenediamine and ammonia were used as reactant gases. The possibilities of establishing the relative molecular masses and the masses of both the sugar residue and the aglycone and some structural and stereochemical features are discussed.     

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 mass spectrometry of halogenoalkanes with tetramethylsilane as reagent gas

Chemical ionization mass spectra of halogenoalkanes (RX) obtained using tetramethylsilane as reagent gas show two major peaks corresponding to the cluster ion RX⁺SiMe₃ and alkyl ion R⁺. Iodides exhibit the highest affinity toward the trimethylsilyl ion and produce the most stable silylated molecular ions, whereas bromides and especially chlorides are less reactive toward Me₃Si⁺ ions and form less stable [M + SiMe₃]⁺ ions.     

Chemical ionization mass spectrometry of nitrosamines

The mass spectra of eight nitrosamines have been recorded, with excitation by chemical ionization (CI) and electron impact (EI). Comparison of the intensities of the base peaks under CI and El conditions gives intensity ratios in the range 1.4-1.9 for low resolution measurements and up to 10 for high resolution measurements, confirming the enhanced sensitivity available in the CI mode.     

Chemical ionization mass spectrometry using ammonia reagent gas. Selective protonation of conjugated ketones

Studies using ammonia as a selective reagent gas in chemical ionization mass spectrometry were extended to conjugated ketones. Their proton affinities were in the range of most nitrogen-containing compounds (> 207 ± 3 kcal/mole), thereby permitting proton transfer from [NH₄]⁺-, leading to well stabilized protonated molecular ions as the most abundant ion products.     

Chemical ionization mass spectrometry of crown ether acetals using isobutane as reagent gas

Isobutane chemical ionization mass spectrometry of crown ether acetals (M), derived from ethanal, give [MH]⁺ ions from which species corresponding to 44 u are successively eliminated. Mechanisms are presented in which these units correspond to (i) ethanal and (ii) oxirane. An accompanying process is the elimination of ethyne. Similar reactions occur in the chemical ionization mass spectrometry of benzo crown ether acetals.     

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.     

Chemical ionization mass spectrometry of some crown ethers

Methane and isobutane chemical ionization mass spectrometry is superior to the classical electron impact technique for the analysis of aliphatic macrocyclic polyethers of the 4n-crown-n type. The latter reagent gas is particularly suited for molecular weight determinations.     

An innovative method for measuring hydrogen and deuterium: Chemical reaction interface mass spectrometry with nitrogen reactant gas

A new method for measuring deuterium isotopic enrichment with CRIMS (chemical reaction interface mass spectrometry) is described. Using nitrogen as the reactant gas in a chemical reaction interface generates molecular hydrogen that provides the H2 and HD from which the deuterium content can be analyzed with a benchtop quadrupole mass spectrometer. Samples of deuterated leucine in unlabeled leucine were used as the primary test species. Detection of deuterium enrichment was accurate, precise, and linear. We used this scheme to evaluate the results of a process to acetylate lysine residues in a peptide-neurotensin. With separation on a C18 column, we found a 61% yield of the desired monoethylated product that had a D/H ratio very close to the theoretical one. Isotope ratio monitoring for deuterated species will be important in metabolism studies where CRIMS generates a comprehensive and quantitative view of products of deuterated precursors. Where concerns about metabolic isotope effects of deuterium are absent, the use of deuterium will enable these studies to be performed with simpler syntheses and at less cost than if using 13C or 15N.     

Quantitatively resolving mixtures of isobaric compounds using chemical ionization mass spectrometry by modulating the reactant ion composition

Acrolein (C(3)H(4)O) and 1-butene (C(4)H(8)) can both be individually detected by proton transfer chemical ionization mass spectrometry (CI-MS). However, because these compounds are isobaric, mixtures of these two compounds cannot be resolved since both compounds react with H(3)O(+) via a proton-transfer reaction to form a protonated molecule that is detected at a nominal mass-to-charge ratio of 57 (m/z 57). While both compounds react with H(3)O(+) only acrolein reacts to any significant extent with H(3)O(+)(H(2)O). Recognizing that the electrical potential applied to a drift tube reaction mass spectrometer provides a simple and effective means for varying the relative intensity of the H(3)O(+) and H(3)O(+)(H(2)O) reactant ions we have developed a method whereby we make use of this reactivity difference to resolve mixtures of these two compounds. We demonstrate a technique where the individual contributions of acrolein and 1-butene within a mixture can be quantitatively resolved by systematically changing the reagent ion from H(3)O(+) to H(3)O(+)(H(2)O) through control of the electric potential applied to the drift tube reaction region of a proton transfer reaction mass spectrometer.     

Analysis of triacetone triperoxide by gas chromatography/mass spectrometry and gas chromatography/tandem mass spectrometry by electron and chemical ionization

The explosive triacetone triperoxide (TATP) has been analyzed by gas chromatography/mass spectrometry (GC/MS) and sub-nanogram detection limits are reported by ammonia positive ion chemical ionization (PICI), electron ionization (EI) and methane negative ion chemical ionization (NICI). Analysis by methane PICI and ammonia NICI gave detection limits in the low nanogram range. Analyses were carried out on (linear) quadrupole and ion trap instruments. Analysis of TATP by PICI using ammonia reagent gas is the preferred analytical method, producing low limits of detection as well as an abundant (greater than 60% of base peak) diagnostic adduct ion at m/z 240 corresponding to [TATP + NH4]+. Isolation of the [TATP + NH4]+ ion with subsequent collision-induced dissociation (CID) produces extremely low abundance product ions at m/z values greater than 60, and the m/z 223 ion corresponding to [TATP + H]+ was not observed. Density functional theory (DFT) calculations at the B88LYP/DVZP level indicate that dissociation of the complex to form NH4+ and TATP occurs at energies lower than peroxide bond dissociation, while protonation of TATP leads to cleavage of the ring structure. These results provide a method for pico-gram detection levels of TATP using commercial instrumentation commonly available in forensic laboratories. As a point of comparison, a detection limit of 15 ng was obtained by flame ionization detection.     

Chemical ionization mass spectrometry of doxylamine and related compounds

The chemical ionization mass spectrometric (CIMS) analysis of doxylamine, N,N-dimethyl-2-[1-phenyl-1-(2-pyridinyl)ethoxy]ethanamine, and related compounds, using both ammonia and methane as reagent gases, is discussed. The two reagent gases did not produce the same major fragment ion for doxylamine. Mechanisms for the fragmentation of doxylamine under either ammonia or methane CIMS conditions are proposed. The mechanisms explain the observation of an m/z 182 fragment ion for doxylamine analyzed under methane CIMS conditions and an m/z 184 product ion detected under ammonia CIMS conditions.     

Pyrolysis–gas chromatography mass spectrometry and field ionization mass spectrometry of polyquinones

Low- and high-molecular mass thermal decomposition products of five polyquinones with different linking aromatic structures have been analyzed by pyrolysis–gas chromatography and by direct (in-source) pyrolysis–field ionization mass spectrometry. The quantity of carboxyl groups present in the polymer is obtained by the amounts of carbon dioxide found by pyrolysis–gas chromatography. Assuming a radical thermal decomposition mechanism the distribution of ketoacidic and quinonoid segments along the macromolecular ladder could be estimated from the high-molecular mass products measured by pyrolysis–field ionization mass spectrometry. A random distribution of the two different segments was found for polyquinones with biphenylene and dibenzofuran subunits, while a structure built up of blocks of two or more identical segments was obtained for polyquinones with dibenzothiophene and diphenylmethane subunits. At the same time the anomalous structural moieties in the polyquinone ladders are also clarified with the help of the identification of the unexpected pyroysis products. Oxidated and bis-dibenzothiophene and bis-diphenylmethane subunits were found. The observed temperature dependence for the appearances of the thermal degradation products indicates that condensation and elimination reactions are taking place under the described pyrolysis conditions. Condensation in the ketoacidic segments forming new quinonoid segments proved to be important in the polymer which was a 100% poly(ketoacid), but negligible in the polyquinones containing ketoacidic segments up to 60%.