Chemical vapour generation

Viera et al.59 used the isotope dilution technique as a calibration procedure for the determination of As, Ge, Hg, Pb, Se and Sn in coal slurries using chemical vapour generation combined with electrothermal vaporization ICP-MS (CVG-ETV-ICP-MS). 

To implement an easy and automated means for chemical vapour generation procedures (hydride generation for arsenic, selenium, etc., and cold vapour mercury), which allows for a reduction on the interferences caused by first-row transition metals (such as copper and nickel). FI methods may be readily coupled with almost all the atomic-based spectroscopic techniques (including graphite furnace atomisers). 

In addition to solid-phase extraction and chemical vapour generation, other sample pretreatment procedures (including liquid-liquid extraction, precipitation, dialysis and even distillation) can be automated and coupled to the spectrometer. 

H. Matusiewicz and M. Slachdnski, Method development for simultaneous multi-element determination of transition (Au, Ag) and noble (Pd, Pt, Rh) metal volatile species by microwave induced plasma spectrometry using a triple-mode microflow ultrasonic nebuliser and in situ chemical vapour generation, J. Anal. At. Spectrom., 2010,25(8), 1324-1333. 

Matousek T. and Sturgeon R. E. (2003) Surfactant-assisted chemical vapour generation of silver for AAS and ICP-OES A mechanistic study, J. Anal. At. Spectrom. 18 487—494. 

PoHL P. and Zyrnicki W. (2001) Study of chemical vapour generation of Au, Pd and Pt by inductively coupled plasma atomic emission spectrometry, J. Anal. At. Spearom. 16 1442-1445. 

Plasma Enhanced Chemical Vapour Deposition (PECVD) Chemical vapour deposition (CVD) reactions commonly occur at high temperatures (Table II). The use of a plasma to generate chemically reactive species in conjunction with CVD overcomes one of the most common... 

Fig. 13.20. Optical heterodyne force microscopy (OHFM) and its application to a copper strip of width 500 nm, thickness 350 nm, on a silicon substrate, with subsequent chemical vapour deposition (CVD) of a silicon oxide layer followed by polishing and evaporation of a chromium layer of uniform thickness 100 nm and flatness better than 10 nm (a) amplitude (b) phase 2.5 [im x 2.5 m. Ultrasonic vibration at fi = 4.190 MHz was applied to the cantilever light of wavelength 830 nm was chopped at fo = 4.193 MHz and focused through the tip to a spot of diameter 2 im with incident mean power 0.5 mW the cantilever resonant frequency was 38 kHz. The non-linear tip-sample interaction generates vibrations of the cantilever at the difference frequency f2 — f = 3 kHz (Tomoda et al. 2003).

Level swell is the mechanism by which runaway chemical reactions vent a two-phase mixture. When a runaway chemical reaction generates gas or vapour, bubbles are formed throughout the bulk of the liquid. Because the bubbles are buoyant, they wijl tend to rise through the liquid in order to disengage at the surface. However, whilst they remain in the liquid, they occupy volume and so cause the... 

To achieve (b), it is necessary to use relief sizing methods that take account of the dynamics of the pressure relief, event. Pressure relief systems for runaway chemical reactions usually discharge a two-phase mixture (see 4.3). If a steady-state calculation were used to size the relief system, then it would be necessary to size it for the volumetric rate of two-phase mixture equal to the volumetric, rate, of gas/ vapour generation at a particular point (e.g. at the relief pressure for vapour systems). This leads to very large calculated relief system sizes. 

In order to predict the beginning of two-phase relief and whether two-phase or single-phase relief should be assumed for relief sizing, the superficial velocity is calculated from the rate at which the chemical reaction generates gas and/or vapour. (The use of this approximation overestimates the superficial velocity.)... 

Hydride and cold-vapour techniques represent a special combination of chemical separation and pre-enrichment with AAS determination, resulting in higher powers of detection for elements with volatile hydrides, eg, As, Bi, Se, Sb, Hg. Recent literature on vapour generation has been reviewed by Hill et al. (1991). Some examples of the use of hydride generation for the analysis of plant material are given by Muse et al. (1989), Leuka et al. (1990) and Ainsworth and Cooke (1990). Hydride generation can also be used with ICP-EAS (see below) and applications have been reviewed (Nakahara, 1991). 

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