The structural elucidation of small molecules using mass spectrometry plays an important role in modern life sciences and bioanalytical approaches. This review covers different soft and hard ionization techniques and figures of merit for modern mass spectrometers, such as mass resolving power, mass accuracy, isotopic abundance accuracy, accurate mass multiple-stage MS(n) capability, as well as hybrid mass spectrometric and orthogonal chromatographic approaches. The latter part discusses mass spectral data handling strategies, which includes background and noise subtraction, adduct formation and detection, charge state determination, accurate mass measurements, elemental composition determinations, and complex data-dependent setups with ion maps and ion trees. The importance of mass spectral library search algorithms for tandem mass spectra and multiple-stage MS(n) mass spectra as well as mass spectral tree libraries that combine multiple-stage mass spectra are outlined. The successive chapter discusses mass spectral fragmentation pathways, biotransformation reactions and drug metabolism studies, the mass spectral simulation and generation of in silico mass spectra, expert systems for mass spectral interpretation, and the use of computational chemistry to explain gas-phase phenomena. A single chapter discusses data handling for hyphenated approaches including mass spectral deconvolution for clean mass spectra, cheminformatics approaches and structure retention relationships, and retention index predictions for gas and liquid chromatography. The last section reviews the current state of electronic data sharing of mass spectra and discusses the importance of software development for the advancement of structure elucidation of small molecules.

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Advances in structure elucidation of small molecules using mass spectrometry

The purpose of this short review is critically to assess the important experiments in gas phase ion chemistry whose correct interpretation can lead to the assigning of structures to organic positive ions. The methods fall into two main categories, (i) the measurement of ion enthalpies and transition state energies for their fragmentations and (ii) the detailed examination of the unimolecular and collision-induced fragmentation behaviour of cations, anions and neutral species. It is argued that in general, none of the above methods alone can suffice for an ion structure determination, but that in combination these techniques provide a powerful tool by means of which ion structures may confidently be assigned.

Assigning structures to ions in the gas phase

L'etude demontre que les radicaux cationiques CH 3 OH +• , CH 3 NH 2 +• et CH 3 Cl +• ont des isomeres stables: • CH 2 OH 2 + , • CH 2 NH 3 + et • CH 2 ClH +

Distonic radical cations in gaseous and condensed phase

Gas-phase chemistry of collisionally activated ions

This short review focuses attention upon the present status of metastable ion studies with emphasis upon the relationship between metastable peak shapes, ion structur and fragmentation mechanisms. Some recommendations are made concerning nomenclature and the reporting of observations on Gaussian-type metastable peaks. Experimental methods for recording relative abundances of metastable peaks are critically appraised. The relationship between metastable ion phenomena and isomerization of gaseous ions is reviewed with particular attention drawn to the effect of rate-determining isomerizations. The shapes of Gaussian-type metastable peaks are discussed in some detail and selected examples from recent studies are used to show that such peaks may, by appropriate experiments, be separated into two Gaussian-type components thus revealing new features of the fragmentation reaction. The magnitude and significance of released kinetic energies, T, are considered and it is stated that few conclusions can be drawn from the evaluation of T alone; the importance of accurate thermochemical data as an aid to understanding and interpreting kinetic energy release data is emphasized. Other topics discussed include composite metastable peaks, metastable peaks produced in chemical ionization and field ionization and the partitioning of internal energy of the fragmenting ion into translational degrees of freedom of the products, for reactions with and without a reverse energy barrier.

The scope of metastable peak observations

THEORY AND METHODS. Tools for Identifying the Structure of Gas Phase Ions. What and What Not to Expect from Gas Phase Ions. ION STRUCTURES.

Assigning Structures to Ions in Mass Spectrometry

Thermochemistry and unimolecular reactions of ionized acetic acid and its enol in the gas phase

Structures of [C4H4O]+.cntdot.ions produced from 2- and 4-pyrone

Correlating thermochemical data for gas-phase ion chemistry

Gaseous [H2, C, N]+ and [H3, C, N]+.cntdot. ions. Generation, heat of formation, and dissociation characteristics of methylenenitrenium(1+) ([H2CN]+), iminomethylene(1+) ([HCNH]+), aminomethylidene(1+) ([CNH2]+), formaldimine(1+.cntdot.) ([H2CNH]+.cntdot.), and aminomethylene(1+.cntdot.) ([HCNH2]+.cntdot.) ions

John L. Holmes

Papers

Assigning Structures to Ions in Mass Spectrometry

Thermochemistry and unimolecular reactions of ionized acetic acid and its enol in the gas phase

Structures of [C4H4O]+.cntdot.ions produced from 2- and 4-pyrone

Correlating thermochemical data for gas-phase ion chemistry