Vapour generation techniques

Mercury generally is found in low and trace concentrations. So there is need to determine Hg in ranges corresponding to various types of water samples. Detection levels of Hg can be improved by the use of vapour generation technique. This technique allows to sepai ate the analyte from the sample matrix and so to overcome the matrix interference. The fluorescence technique, with its high sensitivity and linearity, in combination with vapour generation, provides for a possibility to detect Hg in parts per trillion per liter regions. 

Fig. S. S Membrane separator designed to improve performance of ICP/MS for arsenic and selenium by vapour generation techniques.

Hydride/vapour generation techniques provide extremely good sensitivity. When coupled to continuous flow methodologies for use in routine analysis, simple and reliable analytical techniques are provided. TTie extension of chemistries and sample transfer systems to provide analytical protocols to cope with a wider range of elemental analyses should be pursued in the search for lower detection levels. While multi-element techniques offer very low levels of detection, the use of specific single element analytical instruments with detection capabihties similar to those described above may be the best route for routine laboratories with high sample throughput. 

SEC. S.2] HYDRIDE/VAPOUR-GENERATION TECHNIQUES 163 288,145 counts (0.1 second)... 

There have been a few research papers reporting the use of other vapour generation techniques to volatilize analytes that form unstable hydrides, or had previously been thought not to form vapours at room temperature. Examples include the use of sodium tetraethylborate to form volatile ethyl compounds of cadmium, lead and thallium. 

Chiba et al. [749] used atmospheric pressure helium microwave induced plasma emission spectrometry with the cold vapour generation technique combined with gas chromatography for the determination of methylmercuiy chloride, ethylmercury chloride and dimethylmercury in sea water following a 500-fold preconcentration using a benzene- cysteine extraction technique. 

A surprising addition has recently been made to the list of elements which may be usefully determined by vapour generation techniques, namely cadmium.5 Sodium tetraethylborate was used to produce a volatile cadmium species, with citrate being used to mask interference from nickel and copper. Using an argon-diluted hydrogen diffusion flame as atomizer, the detection limit by AFS was 20 ng l-1. 

Because the hydride and cold vapour generation techniques have so far been used mainly with liquid and dissolved samples, all aspects related to the variables influencing the process and the characteristics of the ensuing methods, among others, have been established in the light of a liquid entering the separator. Most such aspects also affect solid samples and are thus worth some comment, as are those that are exclusive to them — all briefly as this technique has scarcely been applied to solid samples. 

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