Effective thermal desorption of such tubes is difficult to achieve since the sheer bulk of the asorbent material prevents the material from being heated in a uniform fashion. A large quantity of solid adsorbent is required to prevent exceeding the retention capacity of the adsorbent. Standard solid sorbent tubes are of a relatively large size, which is dictated by the requirement to either take air samples over long periods of time or to sample relatively high concentrations of contaminants. While sample tubes packed with a solid adsorbent overcome many disadvantages of the bubbler sampling system, they suffer from other disadvantages. This severely restricts the sensitivity of analysis methods based on bubbler sample collection. In addition, only a very small aliquot of the trapping solvent or liquid charge of the bubbler is needed to perform an analysis. For example, bubblers are relatively large and cumbersome devices that are difficult to use in field trials or large scale sampling networks. By drawing air continuously through analyzers which monitor contaminant concentration in real time or near real time.Īll of these techniques suffer from certain disadvantages. The air is withdrawn from the collection container using a small gas tight syringe and injected into an analysis apparatus.Ĥ. By collecting sample volumes of the air in suitable containers such as large bags or gas syringes. The solid material is subsequently solvent extracted and the extracts analyzed, or the material is heated to thermally desorb the trapped contaminants into an appropriate apparatus for analysis.ģ. The solid material retains contaminants by, for example, physical inclusion in pores or electrostatic attraction at active polar sites on the surface of the solid when air is drawn through the tubes.
By using tubes packed with a solid, porous absorbent. The solution is subsequently analyzed by injection into, e.g., a gas chromatograph.Ģ. Air is drawn ("bubbled") through the liquid which partially or completely dissolves the contaminants and thus removes them from the air stream. By using liquid-filled impingers or bubblers. The current techniques for collecting air samples are:ġ. For example, contaminants may be collected to determine the downwind spread of herbicides or pesticides from a cross-spraying operation, to determine industrial compliance with air quality standards, to monitor workplace air quality or for controlling the use of toxic materials and to monitor and identify toxic substances released during military encounters. The trapping and collection of airborne contaminants in the form of gases, vapours or aerosols is of importance in a number of fields. The present invention relates to the trapping and collecting of airborne contaminants for subsequent analysis.
0 kommentar(er)
