Keith R. Jennings

The observation of metastable transitions in a double-focussing mass spectrometer using a linked scan of the electric sector and magnetic sector fields

A detailed study has been made of the observation of metastable transitions in the first field-free region of a double-focussing mass spectrometer of Nier—Johnson geometry by scanning simultaneously the magnetic field B and the electric sector field E such that B/E remains constant throughout the scan. The B/E linked scan provides a convenient method of determining the daughter ions formed from a chosen parent ion and, because of the transmission characteristics associated with this type of scan, sharp peaks are observed irrespective of the amount of internal energy released as translational energy of the fragments. This greatly facilitates the accuracy with which the mass ratio of parent and daughter ion can be determined and also allows a wide range of mass ratios to be investigated at full source sensitivity. The scan gives equally good results when used to study collision-induced decompositions. The origin of several low-intensity artefact peaks is established and methods of recognising such peaks are discussed. The B/E linked scan complements other methods of investigating metastable transitions already in use and is likely to find most application in the study of analytical problems.

Iron and copper chelation by flavonoids: an electrospray mass spectrometry study

Flavonoids are well known as effective free radical scavengers exhibiting therefore an antioxidant behaviour. Another antioxidant mechanism however may result from the ability they have to chelate metal ions, rendering them inactive to participate in free radical generating reactions. Electrospray mass spectrometry has been used to study metal ion interactions with a set of flavonoids from different classes. Complexes with a range of stoichiometries, of metal: flavonoid, 1:1, 1:2, 2:2, 2:3 have been observed. The stoichiometry 1:2 is in general the preferred one. It is established for flavones and for the flavanone naringenin that the binding metal sites are preferentially at the 5-hydroxyl and 4-oxo groups. Redox reactions are also observed through the change of the oxidation state of the metal, jointly with the oxidation of the flavonoid by loss of hydrogen. Structures of the oxidized species of some flavonoids are proposed.

Collision-induced dissociation of alkali metal cationized and permethylated oligosaccharides: Influence of the collision energy and of the collision gas for the assignment of linkage position

Tandem mass spectrometry has been used to study the collision-induced decomposition of [M+Na]+ ions of permethylated oligosaccharides. It is shown that many linkage positions in one compound may be determined by the presence or absence, in a single spectrum, of specific fragment ions that arise from the cleavage of two ring bonds and that the yield of such ions depends strongly on the collision energy and nature of the collision gas. In contrast to the behavior of monolithiated native oligosaccharides, the collision-induced decomposition of the sodiated and permethylated oligosaccharide samples at low energy leads to preferential cleavage of glycosidic linkages. At high collision energies, the fragment ions formed by cleavage of more than one bond are greatly enhanced, especially when helium is replaced by argon as the collision gas. Furthermore, argon is the more efficient collision gas in inducing fragmentation of the precursor ions. As an example of the application of this method, the discrimination between the 1 → 3 and 1 → 6-linked mannose residues in the common core of N-glycans is described.

The observation of metastable transitions in a double-focussing mass spectrometer using a linked scan of the accelerating and electric-sector voltages

Abstract A method is described for the observation of metastable transitions in the first field-free region of a double-focussing mass spectrometer of Nier-Johnson geometry by scanning simultaneously the accelerating potential V and the energy V. of ions transmitted by the electric sector such that V 1 2 V · is constant. The linked scan provides a convenient method of determining the daughter ions formed from a chosen parent ion and because of the transmission characteristics associated with this type of scan, sharp peaks are observed irrespective of the amount of internal energy released as translational energy of the fragments. This greatly facilitates the identification of daughter ions of adjacent masses but necessarily means that this type of scan gives no information on internal-energy release. Spectra must be obtained at the highest energy resolving power that is practicable in order to minimize the collection of daughter ions formed from precursor ions differing by one mass unit from that under study. Other features arising from decompositions which occur during acceleration and in the field-free region before the magnetic sector are discussed. The technique is a useful complement to others already in use for obtaining information on metastable transitions.

Collision-induced decomposition of ions

Abstract The current status of the understanding of the collision-induced decomposition (CID) of di- and polyatomic ions is reviewed. The fundamental aspects of the CID of diatomic ions is considered in detail as a basis for the understanding of the processes leading to the CID of polyatomic ions. Particular attention is given to experimental and thoeretical work regarding the CID of diatomic ions via vibrational excitation and low energy CID (collision energy

Time-lag focusing and cation attachment in the analysis of synthetic polymers by matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry

Ultraviolet matrix-assisted laser desorption/ionization-mass spectrometry has been employed with time-lag focusing to explore its utility for the characterization of synthetic polymers with broad distributions. Mixtures of five polymer standards with narrow molecular weight distributions were analyzed. The spectra were found to be broadly those expected for three different types of polymer systems—poly(styrene), poly(methyl methacrylate), and poly(ethylene glycol)—when equimass mixtures were used. Large changes in the apparent molecular weight distribution of poly(ethylene terephthalate) were observed when the cation was varied. The shift in the envelope was found to be related to the size and the ability of the oligomers to solvate the cation.

The changing impact of the collision-induced decomposition of ions on mass spectrometry

Abstract The first observations of the products of the collision-induced decomposition (CID) of ions were made in the early days of the development of mass spectrometry and for many years, they were regarded as little more than a nuisance. Early in the 1960s, systematic work on CID began, and, although it proved to be very useful in the investigation of the structures of ions, in general, the mass spectrometry community regarded CID as a subject for fundamental studies but of little value in analytical work. In essence, CID was a technique looking for a problem. With the advent of soft ionisation methods, first fast atom bombardment and later electrospray ionisation and matrix-assisted laser desorption ionisation, all of which gave molecular weight information but no structural information, the situation changed, and CID became an integral part of analytical mass spectrometry. High-performance, compact tandem mass spectrometers based on the quadrupole, time-of-flight and ion trap mass analysers play an increasingly important role in biological mass spectrometry and Fourier transform ion cyclotron resonance instruments provide very-high-resolution CID capabilities. Tandem mass spectrometry is already the method of choice for the sequencing of proteins and will undoubtedly be important in helping us understand protein function.

Conformations of biopolymers in the gas phase: a new mass spectrometric method

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Generation of average mass values and end group information of polymers by means of a combination of matrix-assisted laser desorption/ionization-mass spectrometry and liquid secondary ion-tandem mass spectrometry

Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) and liquid secondary ion-tandem mass spectrometry (LSI-MS/MS) have been applied to the analysis of synthetic polymers to generate values for the average mass and the mass of the end groups. The average mass values were calculated for polymethylmethacrylate and polystyrene standards from the MALDI-MS data. Abundant fragment ions of the polymers, generated by means of LSI-MS/MS, were consistent with the known structures of the end groups of the polymers. Furthermore, losses from the side chains of the polymers were also observed in the LSI-MS/MS spectra.

Ion cyclotron resonance mass spectrometer

This relatively new form of mass spectrometry is proving to be valuable in several branches of chemistry. This review shows that the technique has already yielded some useful data.