Plasma ions, positive

In contrast to the other ionization detectors a decrease in the detector background current is measured rather than an increase in the number of ions or electrons generated. The detector standing current results from the bombardment of the carrier gas by beta electrons forming a plasma of positive ions. 

The plasma is maintained at a temperature of 10 000° C by an external radio frequency current, as described in Section 3.3. At this temperature, many molecular species are broken down, and approximately 50% of the atoms are ionized. So far this is identical to ICP-OES, but for ICP-MS we are not interested in the emission of electromagnetic radiation, but rather in the creation of positive ions. To transfer a representative sample of this plasma ion population to the mass spectrometer, there is a special interface between the plasma and the mass spectrometer. This consists of two sequential cones... 

Electron-capture detectors show great sensitivity to halogenated compounds. In electron-capture detectors, the carrier gas is ionized by beta particles from a radioactive source (usually tritium or nickel-63), to produce a plasma of positive ions, radicals, and thermal electrons. Thermal electrons are formed as the result of the collision of high-energy electrons and the carrier gas. 

At Argonne, a new positive ion injector for ATLAS based on an electron cyclotron resonance (ECR) plasma ion source is under construction (40). The... 

Thermionic converters are high temperature devices which utilize electron emission and collection with two electrodes at different temperatures to convert heat into electric power directly with no moving parts. Most thermionic converters operate with a plasma of positive ions in the interelectrode space to neutralize space charge and permit electron current flow. Both the plasma characteristics and the surface properties of the electrodes are controlled by the use of cesium vapor in thermionic diodes. 

We will now develop the transport equations in L-space from the above Green functions. Following the Keldysh approach in //-space, the transport equations for non-equilibrium plasmas and radiation have been given by DuBois [29]. A similar transport equation for a system of ions may be found in Kwok [30], which is based on the Green function associated with ion positions. In a separate paper [31], we will derive the appropriate transport equations for the coupled system of electrons, ions, and electromagnetic fields. 

Any surface which is in contact with a plasma will be bombarded by electrons and ions. Since electrons escape much faster from the plasma to the surface, a sheath (a positively-charged) region is formed. The electrons are described as being more mobile. In this way a potential difference between a grounded surface and the plasma volume is maintained. This is referred to as the plasma potential (Vp). If the surface is allowed to float, i.e it is not electrically earthed, the floating surface also acquires a negative potential with respect to the plasma. Ions are accelerated across this potential and impart energy to the surface. 

Table 2. Typical Positive Plasma-ions Under the RO Membrane Condition. See Text for Details...

Figure 18. Mass spectrum of positive plasma-ions under the condition of 0.5 torr, Qbz = 400 STP mL/min, Qat = 300 STP mL/min, 40 W, See text for details.

Plasma proteins are amphoteric molecules having both positive and negative charges that contribute to the balance of plasma ions and osmolality, particularly albumin. In cardiotoxicity, plasma protein patterns may be altered with increases of total protein, albumin, and acute phase proteins (e.g., myoglobin, C-reactive protein, and hbrinogen see Chapters 7 and 8). When proteins bind xenobiotics (or metabolites), their contributions to cation/anion balance may be altered. 

In plasmas ions are always under acceleration by the discharge electric field E which is typically 10 V/cm in a positive column. 

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