Impact of space-energy correlation on variable range hopping in a transistor.

Hopping conduction in transistors, i.e., under a transverse electric field, is addressed using percolation theory with a space-energy correlation in the density of states of the impurity band. The computation of the percolation threshold over an extended range of correlation parameters enables us to derive a formula, which, while giving the classical results in the low field limit, describes the emergence of a specific variable range hopping in the high field case. An application of this formula to experimentally extract the localization radius is also proposed.

Analysis of alkenes by copper ion chemical ionization gas chromatography/mass spectrometry and gas chromatography/tandem mass spectrometry

A novel chemical ionization/fast atom bombardment (CI/FAB) source was used to analyse alkenes by chemical ionization mass spectrometry (CI-MS) using copper ions as the ionizing agent. The Cu(+)-CI mass spectra showed abundant pseudomolecular adduct ions [alkene-Cu](+) and characteristic fragment ions. Mass-analysed ion kinetic energy spectroscopy was used to study the product ions resulting from the decomposition of adduct ions and to eliminate background interferences derived from the copper ions. The major fragmentations permitted the localization of double bonds and minor fragments allowed the differentiation of alkene isomers. The CI/FAB source was coupled to a gas chromatograph and simple and complex mixtures of octene isomers were analysed by gas chromatography (GC)/Cu(+)-CI-MS and GC/Cu(+)-CI-MS/MS. Copyright 1999 John Wiley & Sons, Ltd.

Urinary metabolites of oxapadol (MD720111), a new non-narcotic analgesic agent, in the rat, dog and man.

1. A number of metabolites of oxapadol were isolated from urine of rat, dog and man after administration of a single dose of 14C-labelled compound. They were identified by direct inlet mass spectrometry and chromatographic comparison with reference compounds. 2. Oxapadol was extensively metabolized and the unchanged drug was undetectable in rat or human urine; only traces were found in dog urine. Nine metabolites were identified in rat and dog urine, and six in man. 3. The routes of biotransformation were: (a) aromatic hydroxylation, mainly in the benzimidazole ring, (b) scission of the heterocyclic ring following two different pathways, and (c) a combination of the two. Regioselectivity was observed for aromatic hydroxylation, as only three of the four possible monohydroxy oxazepinobenzimidazoles could be detected.