Eric E. Kingston

Occurrence of guanosine 3′,5′-cyclic monophosphate (Cyclic GMP) and associated enzyme systems in Phaseolus vulgaris

Abstract Cyclic GMP, isolated from Phaseolus vulgaris , has been unequivocally identified by NMR and FAB-mass spectrometry with MIKES-scanning. Radioimmunoas

Angle-dependence of ion kinetic energy spectra obtained by using mass spectrometers I. Theoretical consequences of conservation laws for collisions

Collision-induced processes for ion beams in the kilovolt energy range have been studied in mass spectrometers since the inception of the technique (‘Aston bands’). In most such studies to date, the fast collision products bave been collected over a range of angles relative to the initial projectile trajectory, this range being defined by the ion optics of the instrument used. More recently, there has been some interest in controlling and exploiting the collection angle for the fast collision products. The motivation behind such studies may be expressed qualitatively in terms of the more violent collisions favouring higher-energy processes, and also resulting in a larger scattering angle for the projectile ion in the activating collision. Thus, it might be hoped that collection angle could serve as an experimental parameter whose variation controls the energetics of the collision-induced processes actually observed. The present work examines the probable limitations of such an approach, on the basis of classical collision theory. Even without knowledge of an appropriate potential function for the projectile ion-neutral target interaction, it is possible to obtain useful quantitative information concerning such collisions. The extensive work on monatomic projectiles and targets is reviewed, and an attempt made to extend these results to polyatomic species of more interest to the mass spectrometrist. When the collision induced process to be studied is chemical fragmentation, the observed angular distribution is a convolution of two effects of comparable importance, namely the scattering angle-energy deposition relation which is the desired result of the experiment, and the internal energy of the projectile (precursor) ion released as excess translational energy of the fragments. The most recent experimental work on angle-resolved mass spectrometry is critically discussed in the light of these considerations.

The resolution of charge-stripping peaks using charge exchange in a multi-sector mass spectrometer

Abstract The charge-stripping process, when studied in sector mass spectrometers, is often masked by the presence of interfering collision-induced fragmentation processes. This presents problems, for example, in interpreting E/2 spectra which are meant to be representative of the doubly charged ions formed by charge-stripping singly charged ions issuing from the ion source. A method is described for completely resolving the spectrum of doubly charged ions from interferences, which uses charge exchange and a further stage of energy(-to-charge) analysis. A simple modification to a double-focusing mass spectrometer is described for achieving this. Examples of fully “resolved” E/2 and charge-stripping spectra are given.

Angle-Dependence of Ion Kinetic Energy Spectra Obtained by Using Mass Spectrometers. II. Experimental Considerations and Preliminary Results on Non-Fragmenting Systems

Experimental problems associated with studies of the scattering of kilovolt projectile ions in mass spectrometers designed primarily for chemical analysis are discussed. The parameters that are important in satisfactorily controlling and defining the actual scattering angle in relation to the observation angle are considered in detail. Two different experimental configurations are considered; angular selection before, or after kinetic energy analysis of the collision products. A modification to a VG ZAB-2F double-focusing mass spectrometer, in order to observe angle-resolved ion kinetic energy spectra of collisionally scattered ion beams, is described. Initial angle-resolved experiments on systems that do not involve fragmentation, have been performed. The results are presented for the angle-resolved energy loss spectra of Ar+ and N2+ and the angle-resolved charge-stripping of Ar+. A feature of the apparatus described is the small uncertainty in the angular selection of the analysing angle-resolved slit.

Angle-resolved mass spectrometry

Abstract Scattering of ions in the z-direction during inelastic collisions with gas molecules has been used to study the energetics of various ion reactions. Charge-stripping spectra and mass-analysed ion kinetic energy spectra are illustrated as a function of angle. The theoretical basis of inelastic scattering is critically assessed and the importance of pre- and post-collimation of the ion beam stressed.

Is the methylenemethonium radical cation (ĊH2CH4) a stable species

Theoretical and experimental evidence is presented which casts doubt on the recently reported observation of a C2H6+˙ isomer having a methylenemethonium (ĊH2[graphic omitted]H4) structure.