Argon sheath

These workers used a prototype spectraspan III dc plasma echelle spectrometer, 510-512, (Spectrametrics Inc., Andover, Mais.). They adapted a Varian 1200 gas chromatograph for on-column injection onto a 6 ft X g in. o.d. stainless steel column packed with 2% Dexsil 300 GC on Chromosorb 750, 100 120 mesh (Johns-Manvilie Corp., Denver, Col.). Column effluent was split by an approximately 1 1 ratio between the flame ionization detector of the gas chromatograph and a heated, thermal, and electrically insulated 1/16-in. o.d. stainless steel transfer line to the dc plasma. Preheated argon sheath gas was required in addition to the argon supplied to sustain the plasma, in order to optimize spectral sensitivity. The column and injection port temperature were set at 130 and 160 C, respectively, and the interface temperature was 170 0. Helium carrier gas flow rate was 25 ml/min. 

A Doehlert design was applied to investigate the flow ratios of argon (sheath and plasma gas) and oxygen in relation to the signal-to-background ratio. 

Sheath Properties of an Argon-Silane and Two Silane-Hydrogen Discharges"... 

Introduction into a DC plasma requires rather more care and attention owing to its inherent design features. As the hydride is being introduced into the plasma, it is necessary to provide a controlled sheath of argon to contain the hydride and direct it into the plasma. This chimney effect significantly improves the sensitivity for hydride-forming elements. This interface has also formed the basis of an introduction system for mercury vapour into an atomic-fluorescence spectrometer as described by Godden and Stockwell [12]. 

The experimental apparatus consisted of a TEKNA-type induction plasma torch (PL-035LS) with a quartz confinement tube of 25 mm and a water cooled steel chamber connected to a cyclone. The plasma plate power of 21 kW was provided by a four turn, water cooled induction coil from an RF generator operating at an oscillator frequency of 3 MHz. High purity argon was used both as plasma and sheath gas with flow rates of 20 and 601 min-1, respectively. In order to raise the low enthalpy and heat conductivity of the argon plasma gas, hydrogen was also mixed into the sheath gas with a proportion of 10% (v/v). 

Argon was used as the central plasma gas and as the sheath gas, as well. Reagent (H2) or auxiliary (O2) gases were mixed to the sheath gas. Powders were injected axially into the hottest region of the plasma by a PRAXAIR powder feeder through a water cooled probe. Both the raw materials and the products were characterized in terms of particle size, chemical and phase compositions. In each run products were collected from the reactor wall (R), from the reactor bottom (RB) and the cyclone (C). 

The electron temperature (Tg), electron density (ng) and electron energy distribution function for a plasma sustained in an argon/benzene mixture were measured by double and triple plasma-probe methods. Each probe was heated up to 1000 K with a sheathed heater, which was inserted into the probe, in order to prevent... 

The variable magnetic field that is created confines the ions and the electrons to an annular path. As the medium becomes more and more conducting, by appearance of an Eddy current, temperature increases considerably by the Joule effect. The device behaves similar to the secondary coil of a short-circuited transformer. The plasma is isolated from the torch wall by a gaseous sheath of non-ionized argon, which is injected by an external tube concentric to the previous one and is used to keep quartz wall cool. 

Nitrogen or argon is used as a sheathing gas to retard oxidation of the furnace. A rate of 4 liters/min gives adequate protection and reproducible signals for cadmium. The rate of gas flow, however, has a significant effect on the cadmium response, with maximum response at 3-4 1/min. 

Typical spatiotemporal profiles of potential are shown in Fig. 8 [26]. The left electrode is driven by a sinusoidal radio frequency voltage Frf = Fosin(a)t). The case shown is for an argon discharge with Fq = 100 V and u>/2n — 13.56 MHz. The potential distribution is such that the electrodes are bombarded by positive ions during the whole period of the RF cycle, while most electrons are trapped in the plasma. Only electrons with kinetic energy greater than the sheath potential can reach the walls. Electrons leak to the walls during a short time in the cycle when... 

Application to capacitively-coupled reactors Figure 24a shows the electron temperature distribution in an argon discharge sustained in a one-dimensional parallel plate reactor of the kind shown in Fig. 7. The temperature peaks near the plasma-sheath interface, where the product of the current and electric field (Eq. 31) is highest, and steep gradients develop in that region. Electrons which diffuse towards the electrode during the sheath potential minimum (around r = 0.25 at left electrode, see also Fig. 

Detector MS, Finnigan MAT TSQ 7000 triple stage quadrupole, selected reaction monitoring mode (m/z 285/257, offset -30 eV), collision gas argon at 0.27 Pa, heating capillary 250°, repeller 20 V, electrospray capillary 6 kV, electron multiplier 2.3 kV, sheath gas nitrogen at 344.7 kPa, auxiliary gas nitrogen at 5 L/min, octapole offset 5 eV... 

Both turbulent burners and premix burners have been used for atomic fluorescence. The premix burner is usually round in shape (a modification of the Meker-type burner), since this provides better geometry for fluorescence than does a slot burner. For an optimum detection limit, the premix burner is also shielded that is, an inert gas such as argon or nitrogen is directed in a sheath around the flame. This elongates the interconal zone and lifts the secondary reaction zone above the burner, separating it from the lower part of the interconal zone where the excitation beam passes. The result is less background emission and less noise, particularly in hydrocarbon flames like air-acetylene or nitrous oxide-acetylene. The premix burner, especially when shielded, appears to offer increased sensitivity over the turbulent burner. 

Ye, M. L., Hu, S., Quigley, W. W. C., and Dovichi, N. J., Post-column fluorescence derivatization of proteins and peptides in capillary electrophoresis with a sheath flow reactor and 488 nm argon ion laser excitation, J. Chromatogr. A, 1022, 201, 2004. 

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