Reduced-pressure plasmas

Trivalent arsenic and antimony were determined in environmental samples by derivatization and reaction to form stable triphenylarsine and triphenylstibine these were extracted, gas chromatographed and detected at 228.8 nm and 259.8 nm respectively, with detection limits of 

Sklarew and J.C. Evans, Spectrochim. Acta., 1985, 4UB, 357 copyright 1985, Pergamon Press.) 

20 and 50 pg [32]. A parallel study [33] determined alkylarsenic acids in commercial pesticides and environmental samples by borohydride reduction. Reamer et al. determined tetraallqrl lead compounds in the atmosphere after collection in a cold trap [34]. Hydrogen was doped into the plasma to minimize lead build-up on the quartz plasma tube walls. A typical detection limit for tetraethyl lead was 6 pg, and selectivity over carbon was ca. 80,000. 

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Vapor—vapor reactions (14,16,17) are responsible for the majority of ceramic powders produced by vapor-phase synthesis. This process iavolves heating two or more vapor species which react to form the desired product powder. Reactant gases can be heated ia a resistance furnace, ia a glow discharge plasma at reduced pressure, or by a laser beam. Titania [13463-67-7] Ti02, siUca, siUcon carbide, and siUcon nitride, Si N, are among some of the technologically important ceramic powders produced by vapor—vapor reactions. 

A new, low-pressure, plasma-assisted proeess for synthesising diamonds has been found by Roy et al [83,84]. An intimate mixture of various forms of carbon with one of many metals (e.g., Au, Ag, Fe, Cu, Ni) is exposed to a microwave plasma derived from pure hydrogen at temperatures ranging from 600-1000 °C. Roy et al postulate a mechanism in which a solid solution of atomic hydrogen and the metal. Me, facilitates dissolution of carbon to form molten droplets of Me -Cj,-H. Diamonds nucleate at the surface of the droplets as the temperature is reduced. 

Story WC, Caruso JA. 1993. Gas chromatographic determination of phosphorus, sulfur and halogens using a water-cooled torch with reduced-pressure helium microwave-induced plasma mass spectrometry. J Anal Atomic Spectrometry 8 571-575. 

Because MIPs are formed at low temperatures, liquid samples cannot be introduced because they extinguish the plasma, even small amounts of organic vapour. However, the on-line coupling of HPEC to MIP-OES has been described for the speciation of mercury and arsenic compounds. Continuous cold vapour (CV) or hydride generation (HG) techniques were used as interfaces between the exit of the HPEC column and the MIP, held in a surfatron at reduced pressure [24]. 

For the most part, plasma-enhanced etching and deposition are performed in four basic reactor types (Figure 7 2, 46). Each reactor has several basic components a vacuum chamber and pumping system to maintain reduced pressures, a power supply to create the discharge, and gas- or vaporhandling capabilities to meter and control the flow of reactants and products. 

Plasma MS is usually based on quadrupole mass analysers. The atmospheric ICP, optimised for ion formation, is placed on its side facing a sample cone (Fig. 4.3). The mass spectrometer operates at reduced pressure and therefore a two- or three-stage differentially pumped interface is needed to transfer the ions from the plasma to the mass analyser. The interface for GC-ICP-MS is generally the same as for ICP emission systems. In one of the earliest GC-MS speciation studies (Chong and Houk, 1987) a packed GC column was used to obtain mass spectra of organic compounds with detection limits in the range 0.001-500 ngs The effects of isotopic fractionation by natural physico-chemical processes were also studied. 

Atomic emission spectrometry (AES) is also called optical emission spectrometry (OES). It is the oldest atomic spectrometric multielement method which originally involved the use of flame, electric arc or spark excitation. Recently there has been considerable innovation in new sources plasma sources and discharges under reduced pressure. Littlejohn et al. (1991) have reviewed recent advances in the field of atomic emission spectrometry, including fundamental processes and instrumentation. 

Reduced pressure helium MIP-MS has also been used as a GC detector for the separation of phosphorus, sulfur, and halogenated compounds [106-108]. This plasma is particularly well suited to these applications as air entrainment and subsequent high background signals are minimized. Again, heated stainless steel transfer lines are commonly used to connect the GC column to the ICP torch. 

When metamfetamine and amfebutamone (bupropion) were co-administered to 26 subjects, 20 of whom completed the protocol, there was no evidence of additive cardiovascular effects [32], The subjects received metamfetamine 0,15, and 30 mg intravenously before and after randomization to bupropion 150 mg bd in a modified-release formulation or matched placebo. There was a non-significant trend for amfebutamone to reduce metamfetamine-associated increases in blood pressure and a significant reduction in the metamfetamine-associated increase in heart rate. Amfebutamone reduced the plasma clearance of metamfetamine and the appearance of amfetamine in the plasma. Metamfetamine did not alter the peak and trough concentrations of amfebutamone or its metabolites. These findings are relevant to the potential use of amfebutamone in ameliorating acute abstinence in metamfetamine users. However, the risk of seizures during amfebutamone treatment for metamfetamine abuse has not been estimated. 

Plasma treatments using various gases can introduce different functional groups to wood surfaces. They may also be used to improve the adhesive properties of plastic coatings. For example, plasma treatments are used industrially as a method of coating automobile bumpers. However, there are some problems in applying plasma treatments to wood. First, the equipment required for plasma treatments is expensive. Second, it is difficult to treat porous woods with plasma under reduced pressures. The latter problem has led to the investigation of normal pressure plasma treatments of wood. 

In real plasmas departures from thermal equilibrium often occur. For the extreme case, as encountered in plasmas under reduced pressure, the emission or the... 

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