Chemical vapour generation methods

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). 

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. 

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. 

Hydride generation methods involve three or four successive steps depending on the technique used (i) The hydride is generated by chemical reduction of the sample (ii) The formed hydride may be collected in the batch type methods (iii) The hydride is entrained in a gas stream into the atomizer (iv) The hydride is decomposed in the atomizer to form the atomic vapour, and the absorption signal is measured. A number of methods in use are based on this principle, but they differ in the means of reduction, atomization, and sample introduction. 

However, the generation of thin palladium membranes onto ceramic surfaces is more complicated. Methods such as spray pyrolysis (see also Section 4.1.3), chemical vapour deposition and sputtering are used. Another method commonly applied [400] is electroless plating [408]. Palladium particles are produced from palladium solution containing amine complexes of palladium in the presence of reducing agents. Palladium nuclei need to be seeded onto the surface prior to the coating procedure [408]. Ceramic surfaces such as a-alumina are first sensitised in acidic tin chloride and then palladium is seeded from acidic palladium ammonia chloride [408]. 

The basic idea of using TCR in a gas turbine is usually to extract more heat from the turbine exhaust gases rather than to reduce substantially the irreversibility of combustion through chemical recuperation of the fuel. One method of TCR involves an overall reaction between the fuel, say methane (CH4), and water vapour, usually produced in a heat recovery steam generator. The heat absorbed in the total process effectively increases... 

Principles and Characteristics Electron impact (El) ionisation is the original ionisation method (1918). Before 1980, mass spectrometry was merely restricted to electron impact (El), with chemical ionisation (Cl) being applied mainly for those samples which resist generation of satisfactory El data. Nowadays, El is still a widely used universal and nonselective ionisation method. In El, the sample is introduced as a vapour... 

Hydride generation AAS (HGAAS) and cold vapour AAS (CVAAS) are special combinations of chemical separation and enrichment with AAS. In HGAAS the analyte is transformed to a volatile hydride, stripped off by an inert gas and atomized in a quartz tube, flame-in tube etc. About ten elements (As, Se, Bi, Sb etc.) can be determined by this technique. The accuracy and detection limits depend on the proper isolation of the hydride. CVAAS is the universally acknowledged most sensitive method for determination of Hg. The generation of elemental mercury vapour is similar to the hydride generation however the quartz cell may not be heated and this gives the name of the method. 

Probably the most common separation systems used in the laboratory today require the sample to be in solution (e.g. HPLC, CE). The solvent may be aqueous or solvent based. However, onemL of such solution yields far too much vapour (1-2L) to be accommodated by a mass spectrometer s vacuum system. Thus the aim of a sample introduction system for such solutions would require the sample to be ionised and the solvent to be separated from these sanple ions. In addition the interface must maintain the integrity of the chromatography. The chromatographic separation must be maintained as well as allowing sufficient analyte through to generate a mass spectmm. A number of methods have been developed to do this, but the two main techniques used today are electrospray and atmospheric pressure chemical ionisation (APCI for short). These are described below under ionisation techniques. 

We would like to mention one further practical application of standard Raman spectroscopy, namely the method of Raman lidar, which is now routinely used to monitor the upper atmosphere for composition (e.g. the presence of water vapour), chemical processes (e.g. the generation or depletion of ozone (O3)), and the determination of temperature profiles at high altitudes. Although absorption and fluorescence lidar systems are also widely used, Raman lidar has the distinct advantage that it is a simultaneous multispecies measurement technique, and that only a single fixed-wavelength laser is required. 

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