The proton affinities (PA) of the 2-, 3- and 4-fluorophenols and related anisoles have been determined with the use of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Based on proton equilibria with suitable reference bases the following proton affinities have been obtained: 788 kJ mol(-1) (2-fluorophenol), 802 kJ mol(-1) (3-fluorophenol), 775 kJ mol(-1) (4-fluorophenol), 808 kJ mol 1 (2-fluoroanisole), 825 kJ mol(-1) (3-fluoroanisole) and 795 kJ mol(-1) (4-fluoroanisole). The experimental proton affinities have been evaluated on the basis of ab initio calculations performed with the G3, G3(MP2) and MP2(fc)/6-11G(2d,p)//HF/6-31G(d,p) procedures. The main aspects of the calculations are: (i) the G3( MP2) proton affinity for the most basic site in each molecule is in good agreement with the experimental value, (ii) the values calculated at the MP2 level are systematically lower than the experimental values and (iii) the relative order of the proton affinities is essentially the same at the different levels of theory. The calculations indicate that the 4- position of the aromatic ring is the most basic site in 2- and 3-fluorophenol, whereas the 2-positon of 4-fluorophenol is associated with the higher proton affinity. For the fluoroanisoles, only MP2-calculations were performed and exclusively for the ring position expected to be associated with the higher PA value.
This review is devoted to the main advances in the investigation of ion/molecule reaction dynamics since the last International Mass Spectrometry Conference. Developments of the experimental techniques to prepare the reactants in selected internal states and well-defined collision energies and to analyse the internal state, the kinetic energy and angular distribution of the products are described. Examples of kinetic and internal energy effects on reaction dynamics are presented for simple systems such as (Ar, N2)+ and (Ar, O2)+ as well as for polyatomics: Ar+ + H2O, He+ + N2O, MH+ + MH and (COS, C2H2)+, for which state-selected or state-to-state studies have been performed. Complementarity of the various techniques is shown. Recent advances in very low temperature studies are also presented. Theoretical interpretations of the experimental results are described but no detail on the theoretical investigations is given. The need for further developments in the experimental and theoretical methods is underlined and some of the possible trends are mentioned.
This review attempts an in-depth evaluation of progress and achievements made since the last 11th International Mass Spectrometry Conference in the application of mass spectrometric techniques to biochemistry and biomedicine. For this purpose, scientific contributions in this field at major international meetings have been monitored, together with an extensive appraisal of literature data covering the period from 1988 to 1991. A bibliometric evaluation of the MEDLINE database for this period provides a total of almost 4000 entries for mass spectrometry. This allows a detailed study of literature and geographical sources of the most frequent applications, of disciplines where mass spectrometry is most active and of types of sample and instrumentation most commonly used. In this regard major efforts according to number of publications (over 100 literature reports) are concentrated in countries like Canada, France, Germany, Italy, Japan, Sweden, UK and the USA. Also, most of the work using mass spectrometry in biochemistry and biomedicine is centred on studies on biotransformation, metabolism, pharmacology, pharmacokinetics and toxicology, which have been carried out on samples of blood, urine, plasma and tissue, by order of frequency of use. Human and animal studies appear to be evenly distributed in terms of the number of reports published in the literature in which the authors make use of experimental animals or describe work on human samples. Along these lines, special attention is given to the real usefulness of mass spectrometry (MS) technology in routine medical practice. Thus the review concentrates on evaluating the progress made in disease diagnosis and overall patient care. As regards prevailing techniques, GCMS continues to be the mainstay of the state of the art methods for multicomponent analysis, stable isotope tracer studies and metabolic profiling, while HPLC—MS and tandem MS are becoming increasingly important in biomedical research. However, despite the relatively large number of mass spectrometry reports in the biomedical sciences very few true routine applications are described, and recent technological innovations in instrumentation such as FABMS, electrospray, plasma or laser desorption have contributed relatively much more to structural biology, especially in biopolymer studies of macromolecules rather than to real life biomedical applications on patients and clinical problems.
This short article focuses attention on two areas of thermochemical concern. The first is the problem of determining enthalpies of formation of free radicals from ion-based experiments. A signal lack of success has attended the determination of Δ H°f298 for the vinyl radical, a value which leads to the bond strength in ethene, a basic thermochemical quantity. In marked contrast the appearance energy method has provided very satisfactory data for alkyl, alkoxy and other radicals. The second area of concern is the significance of threshold appearance energies and the “temperature” of the product species. For dissociative ionization of diatomic molecules the zero Kelvin notation for the threshold products appears to be correct, but for metastable, polyatomic, odd-electron ions the foregoing is probably an oversimplification. Concluding remarks call for new experimental methods to identify and measure the thermochemistry of ion/molecule, ion/radical and H-bridged odd-electron ions.
The elucidation from a molecular point of view of the differences and similarities in the properties and reactivity of matter in the gaseous compared to the condensed state is a subject of considerable current interest. One of the promising approaches to this problem is to utilize mass spectrometry in conjunction with laser spectroscopy and fast-flow reaction devices to investigate the changing properties, structure and reactivity of clusters as a function of the degree of solvation under well-controlled conditions. In this regard, an investigation of molecular cluster ions has provided considerable new insight into the basic mechanisms of ion reactions within a cluster, and this paper reviews some of the recent advances in cluster production, the origin of magic numbers and relationship to cluster ion stabilities, and solvation effects on reactions. There have been some notable advances in the production of large cluster ions under thermal reaction conditions, enabling a systematic study of the influence of solvation on reactions to be carried out. These and other new studies of magic numbers have traced their origin to the thermochemical stability of cluster ions. There are several classes of reaction where solvation has a notable influence on reactivity. A particularly interesting example comes from recent studies of the reactions of the hydroxyl anion with CO2 and SO2, studied as a function of the degree of hydration of OH−. Both reactions are highly exothermic, yet the differences in reactivity are dramatic. In the case of SO2, the reaction occurs at near the collision rate. By contrast, CO2 reactivity plummets dramatically for clusters having more than four water molecules. The slow rate is in accord with observations in the liquid phase.
In the past isotope dilution mass spectrometry (IDMS) has usually been applied using the formation of positive thermal ions of metals. Especially in calibrating other analytical methods and for the certification of standard reference materials this type of IDMS became a routine method. Today, the progress in this field lies in the determination of ultra trace amounts of elements, e.g. of heavy metals in Antarctic ice and in aerosols in remote areas down to the sub-pg g-1 and sub-pg m-3 levels respectively, in the analysis of uranium and thorium at concentrations of a few pg g-1 in sputter targets for the production of microelectronic devices or in the determination of sub-picogram amounts of Th-230 in corals for geochemical age determinations and of Ra-226 in rock samples.During the last few years negative thermal ionization IDMS has become a frequently used method. The determination of very small amounts of selenium and technetium as well as of other transition metals such as vanadium, chromium, molybdenum and tungsten are important examples in this field. Also the measurement of silicon in connection with a re-determination of Avogadro's number and osmium analyses for geological age determinations by the Re/Os method are of special interest.Inductively-coupled plasma mass spectrometry is increasingly being used for multi-element analyses by the isotope dilution technique. Determinations of heavy metals in samples of marine origin are representative examples for this type of multi-element analysis by IDMS. Gas chromatography-mass spectrometry systems have also been successfully applied after chelation of metals (for example Pt determination in clinical samples) or for the determination of volatile element species in the environment, e.g. dimethyl sulfide. However, IDMS-especially at low concentration levels in the environment-seems likely to be one of the most powerful analytical methods for speciation in the future. This has been shown, up to now, for species of iodine, selenium and some heavy metals in aquatic systems.
This review deals with theoretical advances and their application to mass spectrometry and gas phase ion chemistry with special attention given to progress made in the last three years. The following aspects of gas phase ion chemistry will be treated: unimolecular reactions; ion/molecule reactions; rate-energy dependences; and kinetic energy releases. The following reaction systems will be discussed in some detail: SN2 and proton transfer reactions; HeH+2 → HeH+ + H; C6H5Br.+ → C6H+5 + Br.; H+ (NH3)n → H+ (NH3)N-1 NH3; C2H5Cl.+ → C2H.+4 + HCl Co+ + C3H8 → Co+ − C2H4 + CH4; C+60 → C+58 + H2; CH3C6H4I.+ → C7H+7 + I. Theoretical modeling has involved recent extensions of RRKM-QET and phase space theory, in particular, through the use of variational transition state theory. Attention will be drawn to the concept of thermal kinetics in small systems. Theoretical modeling has been crucial for the derivation of important data from experimental results, for example, binding energies and activation parameters. New developments in experimental methods have required new advances in the theoretical modeling. This will be demonstrated when treating the IR radiative decay of long-lived polyatomic ions. Several special topics will be discussed: intramolecular vibrational energy relaxation; isolated state decay; tunneling; and the role of angular momentum.
Since there are 83 natural elements, any review of the use of mass spectrometry for the study of abundance and isotopic compositions of individual species in a geological environment, including locations beyond the Earth, has of necessity to be selective. This paper will focus on the studies of the so-called "light elements": hydrogen, carbon, nitrogen, oxygen, silicon and sulphur and their isotope systems. Five of the elements chosen (H, C, O, N and Si) are amongst the most abundant in the cosmos, four (H, C, O and N) contribute substantially to life processes and choosing either C or Si together with O would allow us to account for > 60% of virtually all rocks. To further restrict the subject matter, I intend to concentrate on advances in the techniques for meaurement of these elements.Amongst the most important advances in technology are the following: (i) the reduction of sample requirements for gas source stable isotope mass spectrometry into the picomole range; (ii) the application of focussed lasers as a means of extracting gas for isotopic measurement; (iii) a demonstration of the abilities of the ion microprobe (SIMS) in producing isotope measurements; and (iv) coupling of gas chromatography to stable isotope mass spectrometers for compound specific isotope analysis of complex mixtures.Some of the scientific highlights which have been achieved by the above means are respectively: (i) the identification of individual silicon carbide minerals as grains of interstellar dust; (ii) the demonstration of growth effects in diamonds of terrestrial and extraterrestrial origin; (iii) mineral specific isotopic compositions for complex geological materials; and (iv) unravelling the origin of mixtures of biomarkers in sedimentary environments.
