Figure 2-3. Absorption devices for collecting gaseous or vapor forms
of soluble contaminants. Gas washing (A and B); helical (C);
fretted bubbler (D); glass-bead contaminants (E).
(2) In the case of insoluble contaminants, adsorption devices such as
charcoal tubes and silica gel tubes (see Figures 2-4 and 2-5) can be used to collect and
concentrate the contaminant, for further analysis. These devices use a medium, to the
surface of which the contaminant adheres. Again, it will be necessary to keep accurate
data on the flow rate of the pump and the duration of the sampling period, in order to
determine the volume of the sample.