Norman S. Ham

He(I) and He(II) photoelectron spectra of glycine and related molecules

Abstract Photoelectron spectra obtained by He(I) and He(II) excitation of glycine, sarcosine and glycine methyl ester are presented. The p-type bands in the He(I) spectrum of glycine are interpreted in terms of localized molecular orbitals; the C 2s bands are identified in the He(II) spectrum. He(I) spectra of some N-acetylamino acids and of a variety of α-and ω-substituted amino acids are also reported.

The photoelectron spectra of amino-acids : A survey

Photoelectron spectra, excited by He I radiation, of the following amino acids were measured:- alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophane, tyrosine, 4-hydroxyproline, β-alanine, γ-aminobutyric acid and δ-aminovaleric acid. The spectra showed a number of bands of low ionization energy (<13 eV) and these have been assigned to photoionizations from the NH2 and COOH groups. For the α-amino acids with complex side-chains extra bands arising from easily-ionizable electrons in aromatic rings or atomic lonepairs, such as sulphur or oxygen atoms, were also identified. Perturbation arguments together with the spectra of closely related molecules have been used to confirm the assignments. During measurement, decomposition occurred for aspartic acid, asparagine and histidine, while glutamic acid and glutamine cyclized.

Graphite furnace mass spectrometry of cobalt

Abstract The atomisation of Co has been investigated in a pyrolytically coated graphite furnace operating in vacua with rapid scan mass spectrometric detection, and by thermochemical calculation of the equilibrium in the furnace during atomisation. The calculations show that the atomising reaction should be Co(s) → Co(g) for both nitrate and chloride samples at the observed appearance temperature for Co atoms. Neither CoO(g) nor Co2(g) were detectedby mass spectrometry during atomisation, but CoCl2(g) was detected from chloride samples during the ashing cycle. Appearance temperatures for Co may be estimated from semilog plots of the calculated equilibrium intensities of Co(g) with temperature, and show good agreement with experimentally determined values. Comparison of the equilibrium calculations with activation energies derived from Arrhenius plots by other workers indicates that the atomisation is thermodynamically controlled in the region of the appearance temperature.

He(I)/He(II) photoelectron band intensity ratios for simple organic molecules

Abstract Band intensifies in the He(I) and HE(II) photoelectron spectra of some simple organic molecules (methanol, methylamine, formaldehyde, acetaldehyde, formic acid, acetic acid, methyl formate, ethylene, butadiene and methyl isothiocyanate) have been measured. The relative band intensity ratios for a number of ionizations from n and π orbitals are presented.

NMR Studies of Solution Conformations of Physiologically Active Amino-Acids

Amino-acids and amines derived from them are of great importance in the central nervous system. The active metabolic role of amino-acids in the brain has been known for a long time and the abnormality of supply and metabolism of some amino-acids has been found to be associated with certain inherited mental disorders. Recently evidence has been obtained that the amino-acids glutamic and γ-aminobutyric acid have important functions as neurotransmitters [1,2].

Atomization problems in atomic absorption spectroscopy—IV: Impact devices, spray chambers and interferences

Abstract A study is made of the effect of the design and position of impact devices on the nebulization efficiency and the extent of volatilization interferences in atomic absorption measurements using an air-acetylene flame. Experiments are described using new designs of spray chamber, either alone or following a tapered spray chamber. The most effective way of reducing volatilization interferences is to force the aerosol to pass through a jet and impinge on a flat surface, either at an impact device or in a spray chamber. This always involves a decrease in the analytical signal, but the signal-to-noise ratio is essentially unchanged. The aerosol transport model of Browner, Boorn and Smith is applied, with modifications where necessary, to calculate the cut-off characteristics of some of the systems studied. Drop-size distribution measurements made on some of the spray chambers substantiate the conclusion that reduction of volatilization interferences and the concomitant loss of analytical signal are due to the selective removal of the larger droplets of the aerosol. For several well-known volatilization interferences, values are derived for the limiting diameters of droplets which can be effectively vaporized in the air-acetylene flame under the experimental conditions used.

Atomisation and chemical ionisation of Si, Ge and Sn in fuel-rich flames

Abstract The relationship between atomisation and ionisation for Si, Ge and Sn in fuel-rich C 2 H 2 and H 2 flames has been studied by means of flame ionisation mass spectroscopy, thermochemical calculation of burnt gas equilibrium composition, and computer simulation of chemical ionisation kinetics. The mass spectra obtained from C 2 H 2 /Ar/O 2 flames are similar to those from H 2 diffusion flames: Sn yields Sn + and SnOH + , Ge and Si yield GeOH + and SIO + . These similarities are in contrast to the substantial differences in calculated atomisation found between the C 2 H 2 and H 2 flames. The discrepancies between atomisation and ionisation are reconciled by a chemical ionisation mechanism in which the ions SiH + , GeH + and SnH + are important intermediates. The ratios of atomic ions to protonated monoxides, M + :MOH + are determined by the thermochemistry for the reaction, MOH + + H ⇌ M + + H 2 O.