Fast Atom Bombardment Ion Source Research Articles

Automation Highlights from the Literature

Automation Highlights from the Literature

Development of a miniaturized multi-turn time-of-flight mass spectrometer with a pulsed fast atom bombardment ion source.

A miniaturized multi-turn time-of-flight (TOF) mass spectrometer with a pulsed fast atom bombardment (FAB) ion source (FAB-MULTUM) has been designed and constructed in order to overcome the drawbacks associated with magnetic sector type instruments utilizing a FAB ion source such as size and weight. This instrument consists of a pulsed FAB ion source, a multi-turn TOF mass spectrometer, a detector, vacuum system, and electronic circuits. The size and weight of the system are less than H520 mm x L580 mm x W230 mm and 45 kg (including vacuum pumps and electronic circuits). The achieved resolving power and mass accuracy of this instrument were > 25000 and about 1 ppm, respectively, which are equivalent to those of magnetic sector type instruments, although the size and weight are much smaller than those of magnetic sector type instruments. The experimental results led us to the conclusion that this instrument enables accurate mass measurements and is a powerful tool for the confirmation of synthesized compounds.

Cu + Chemical Ionization for Analysis of Hydrocarbons by Gas Chromatography/Mass Spectrometry

The use of copper ions for chemical ionization (CI) coupled with gas chromatography/mass spectrometry (GC/MS) of hydrocarbons is reported. Cu +–CI was performed in a high-pressure, fast atom bombardment ion source coupled with both a gas chromatograph and a mass spectrometer. The suitability of the Cu +–CI method is illustrated by the analysis of pure alkylbenzenes, alkylthiophenes, octenes, and by the analysis of a light mixture of aromatic hydrocarbons. The Cu +–CI/GC mass spectra display an abundant [M+ 63Cu] + ion, together with fragmentations, that are of structural interest. The detection limit for isobutylbenzene, taken as model compound, is 100 times lower than that for electron ionization.

If the ionization mechanism in fast-atom bombardment involves ion/molecule reactions, what are the reagent ions? The time dependence of fast-atom bombardment mass spectra and parallels to chemical ionization

The evaporation in vacuo of the matrices used and the particle-induced desorption of matrix molecules in fast-atom bombardment (FAB) contribute to a proposed high pressure region above the FAB matrix known as the selvedge region. If the neutral number density is sufficiently high, ions formed upon bombardment may undergo collisions with molecules, yielding matrix-related cluster ions and, in cases when the analyte is desorbed in neutral form, protonated and deprotonated analyte molecules. Similarities with the chemical ionization (CI experiment have been pointed out previously and are further developed here. If FAB is similar to CI, then the response depends on the structures of the reagent ions — those ions that react with gas phase analyte molecules. We consider here the time dependence of positive and negative ion FAB spectra to attempt to identify the reagent ions of FAB. A model is suggested for the FAB ion source which evaluates similarities to a CI source, as well as spatial aspects that are unique to desorption/ionization techniques.

Injection of reagent ions into the selvedge region in fast-atom bombardment mass spectrometry

A divided probe that incorporates a potassium aluminosilicate glass target and an analyte/glycerol matrix target, spatially separated, was used to inject potassium ions (K +) into the high-pressure “selvedge” region formed above the analyte/glycerol matrix target during fast-atom bombardment (FAB); [M + K] + adduct ions that represent the types of gas-phase neutral molecules present in the selvedge region are observed. Computer modeling assisted in designing the divided target and an additional ion optical element for the FAB ion source to optimize interactions between K + ions and the desorbed neutral molecules. The capability of injecting K + ions into the FAB experiment has utility in both mechanistic studies and analyses. Experimental results here are consistent with a model for the desorption/ionization processes in FAB in which some types of neutral analyte molecules are desorbed intact and are subsequently protonated by glycerol chemical ionization. Unstable protonated molecules undergo unimolecular decomposition to yield observed fragment ions. The use of K + cationization of analytes for molecular weight confirmation is demonstrated, as well as its utility in FAB experiments in which mixtures are encountered.

Quantitation of stable isotopic tracers of calcium by fast atom bombardment mass spectrometry.

Instrumentation and methodology developed for quantitation of stable isotopic traces in urine are described. Calcium is isolated from urine as the insoluble oxalate salt which is subsequently dissolved in hydrochloric acid. The isotopic content of the acid solution is determined by use of a conventional mass spectrometer equipped with a fast atom bombardment ion source. Calcium ions are desorbed from the sample surface by a beam of high-energy xenon atoms and detected with a high-resolution mass spectrometer. A data acquisition system has been developed to control the mass spectrometer and record the ion signals. Detailed analysis of potential sources of error indicates that the precision of the method is presently limited primarily by an isotope effect that occurs during ion desorption. Results presented here demonstrate that the relative abundances of calcium isotopes in urine can be determined with high precision (coefficient of variation < 0.2%) and that the method is a viable alternative to conventional thermal ionization mass spectrometry. The method is especially attractive because it uses a conventional high-resolution mass spectrometer which is routinely used for analysis of organic substances.

Reduction of Aryl Halides and N-Hydroxy Nitrogen Compounds in Fast Atom Bombardment Mass Spectrometry

Abstract Aromatic halogenated compounds and N-hydroxy nitrogen compounds were reduced to dehalogenated and deoxy analogs, respectively, in the fast atom bombardment ion source of a mass spectrometer. The reaction was found to occur in the liquid phase on exposure to a neutral fast atom beam.

Production and release of ions in the Fast Atom Bombardment ion source

FAB spectra have been obtained from several organic diammonium salts. The free dication was observed in only one case. Solid samples of the salts did not yield simply interpretable data. Mass spectra of the salts from a glycerol or glycerol/inorganic salt matrix exhibit several cation and anion related peaks as well as numerous singly charged fragment ions corresponding to charge separation, dealkylation, and elimination reactions accompanied by hydrogen transfer. These results point to low energy desorption pathways of preformed ions from immobile solid phases and mobile, concentrated liquid or high pressure gas phases.

Fast atom bombardment mass spectrometry of the large oligopeptides melittin, glucagon and the B chain of bovine insulin

Application of developments in the fast atom bombardment ion source and high field magnet technology are presented, which together have resulted in the ability to obtain mass spectra from involatile compounds with molecular weights in excess of 3000 daltons. Examples include resolved molecular species from melittin, glucagon and the oxidized form of the B chain of bovine insulin. It is concluded that there now exists a genuine requirement for extended mass range facilities to be available on a routine basis.