Tubes Handbook 18th Edition (EN) - May 2018

|59
Ci
Using the Dräger sampling system, hazardous substances in
the air are collected using a suitable medium via adsorption or
chemisorption. The sample is then analysed in the laboratory
by means of various analytical methods like gas
chromatography (GC), high performance liquid
chromatography (HPLC), UV-VIS photometry, or IR
spectroscopy.
In the case of a stationary measurement the sampling system
is placed at the chosen measurement site for the duration of
sampling. When performing personal air monitoring the
sampling system is attached to the clothing of the person as
close as possible to the inhalation area.
Active Sampling
For active sampling the air to be evaluated is drawn through
a sampling tube with a pump. The substance to be collected
accumulates on the adsorbent.
D-1229-2009
Pump
mi
Grain of
activated
charcoal
Measurement principle of active
sampling with Dräger activated
charcoal tubes
Taking the contaminant mass (mi), determined by the
laboratory analysis and the air volume (V) drawn through the
sampling tube, the concentration (ci), of the contaminant can
easily be calculated:
m i
c i = ——— [mg/m 3 ]
V
Adsorption
layer
The sampling tube features a primary adsorption layer and a
secondary layer which are analysed separately in the
laboratory. This separate analysis determines whether the
entire amount of the measured substance was adsorbed.
During sampling the measured substance is first adsorbed at
the primary adsorption layer. Sometimes the capacity of this
layer is not sufficient, and there is break through resulting in
additional adsorption at the secondary layer. When this occurs
Backup
layer
Dräger sampling tube
a new sample must be taken because it is not possible to be sure that the entire amount
was adsorbed by the two layers (i.e. the secondary layer could also have experienced
break through).
D-1234-2009