Ionization mechanisms responsible for the formation of prepeaks and afterpeaks on Ion signals observed In pulsed glow discharges and potential analytical use of pulsed glow-discharge mass spectrometry have been investigated. The formation of a prepeak at the beginning of the pulse Is related to the Ionization efficiency of electrons accelerated across the cathode fall region. The appearance of an afterpeak at the termination of the discharge is associated with the energy, population, and Ionization efficiency of metastable discharge gas atoms. As a result of the differences In pulse profiles, It Is possible to acquire data over specific regions of the pulse that permit discrimination against Interfering signals In the mass spectrum.

A pulsed glow discharge, rather than a conventional constant dc voltage discharge, is used as an ion source for a quadrupole mass spectrometer. Both sputter yield and ion signal are enhanced by using the pulsed system because of an increase in the voltage necessary to maintain a constant average current at the cathode over the pulse period. Irregularities are seen in the pulse spectrum that appear as rapid surges in the ion signal for both sputtered and contaminant gas species. These peaks appear at the beginning of the pulse for gaseous species but are limited to the postpulse period for sputtered species. Differences in the signal forms allow for the discrimination against selected types of ion signals by using narrow data collection gates placed over different portions of the pulse period.

The glow discharge (GD) is an old source that is finding many new uses in analytical spectroscopy. Its simplicity of operation, coupled with versatility of application, has led to increasing commercial interest. From an obscure analytical method focusing primarily on metal analysis, the glow discharge has developed into a sophisticated technique suitable for analysis of nonmetals, thin films, semiconductors, insulators, and organic materials. More effort is also being made to understand better the many chemical and physical phenomena that influence the effectiveness of the GD source.The GD is a low-pressure (0.1-10 Torr) plasma composed of two electrodes immersed in a partially ionized noble gas (1). The name arises from the

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A lipid bilayer of glycerolmonoleate is spanned over a microscopic shallow groove etched into the 110 surface of a silicon wafer and insulated by thermal oxidation. The conductance of the bimolecular membrane is modulated by gramicidin. The voltage profile in the groove is recorded by a set of Ag/AgCl electrodes which are integrated into the bottom of the groove. It is used to determine the distribution of ion channels along the membrane on the basis of Kelvin's cable equation.