Collision gas thickness

All mass spectra were obtained on a PE-Sciex triple quadrapole instrument (model API III) as described (3). Collisionally induced dissociation (CID) MS/MS experiments were performed in the positive ion detection mode with the orifice potential set at +50 V and the argon collision gas thickness maintained at 315 X lO molecules/ cm. Product ion scans were averaged over a range of 50-600 u in 0.1 u intervals for a dwell time of 1 msec, per interval. 

Q3 was scanned in steps of 0.1 Th, with a dwell time of 1 ms per step. Argon was used as collision gas. (a) Conventional collision cell, 140 eV collision energy, and collision gas thickness 38 x... 

Examples of these scan modes will be described below, however a fundamental description of each will be provided in this section. All three MS/MS scans require Q1 and Q3 resolving and a collision gas (usually Argon) must be present in Q2 at a typical target thickness of ca. 10 cm"2 or 10" torr pressure. The nominal ion energy through the Q2 collision cell is ca. 70eV. 

High-throughput bioanalysis screening approaches involve the characterization of full-scan mass spectra and MS/MS properties to determine the predominant molecular and product ions, respectively. This information is useful for the selection of appropriate ions for selected reaction monitoring (SRM) experiments. Settings such as collision energies and collisionally induced dissociation (CID) pressure or gas thickness can be optimized as well. Typically, the most abundant product ion is selected for SRM. Various acquisition software programs are used to perform the experiment, display the results, and process the data in an automated fashion. 

Porous Membrane DS Devices. The applicability of a simple tubular DS based on a porous hydrophobic PTFE membrane tube was demonstrated for the collection of S02 (dilute H202 was used as the scrubber liquid, and conductometric detection was used) (46). The parameters of available tubular membranes that are important in determining the overall behavior of such a device include the following First, the fractional surface porosity, which is typically between 0.4 and 0.7 and represents the probability of an analyte gas molecule entering a pore in the event of a collision with the wall. Second, wall thickness, which is typically between 25 and 1000 xm and determines, together with the pore tortuosity (a measure of how convoluted the path is from one side of the membrane to the other), the overall diffusion distance from one side of the wall to the other. If uptake probability at the air-liquid interface in the pore is not the controlling factor, then items 1 and 2 together determine the collection efficiency. The transport of the analyte gas molecule takes place within the pores, in the gas phase. This process is far faster than the situation with a hydrophilic membrane the relaxation time is well below 100 ms, and the overall response time may in fact be determined by liquid-phase diffusion in the boundary layer within the lumen of the membrane tube, by liquid-phase dispersion within the... 

The uniformity of the deposited layer (Table 9.1, no. 3) also differs in both deposition technologies. In OVPD the organic molecules are randomly distributed by intermolecular collisions with carrier gas molecules which results in a very uniform and quantitative coverage of the substrate. OVPD thus also has the potential to cover unintended substrate non-uniformities, for example defects or particles. Consequently OVPD can also be applied to complex three-dimensional structured substrates. A single layer of Alq3, deposited by OVPD on a silicon wafer had a thickness uniformity of only 0.6% standard deviation, and surface roughness analysis by AFM confirmed, with an RMS value of 0.6 nm, that the thickness deviation of the Alq3 -layer is already in the molecular dimension [20]. 

An elegant yet technically simple method to determine surface loss probabilities is the cavity technique [30,36-38] A cavity with a small entrance slit (see Fig. 11.2) or a different well-defined geometry - [39-41] is exposed to a flux of reactive species. The transport of the particles is studied via the cross-sectional film thickness profiles. The dimensions of the geometry are chosen much smaller than the mean free path of the neutral radical species so that gas phase collisions are negligible. Then the normalized profiles depend on the surface loss probability (3 only. If the total fluence of particles into the slit is not known no conclusions can be drawn concerning the sticking coefficient except s < / . 

Basic mechanisms involved in gas and vapor separation using ceramic membranes are schematized in Figure 6.14. In general, single gas permeation mechanisms in a porous ceramic membrane of thickness depend on the ratio of the number of molecule-molecule collisions to that of the molecule-wall collisions. In membranes with large mesopores and macropores the separation selectivity is weak. The number of intermolecular collisions is strongly dominant and gas transport in the porosity is described as a viscous flow that can be quantified by a Hagen-Poiseuille type law ... 

Fig. 5. Impact parameter dependence of energy loss in collisions of 100 keV protons with argon atoms determined using equation (50) with G(i7, given by equation (52) (thick curve). The results obtained in the LDA approach and that for the static electron gas (e(k,

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