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ORSA5 diffusion tube comprises a glass sampling
tube open at both ends and filled with activated charcoal.
Each opening in the sampling tube is filled with a cellulose
acetate diffusion barrier as the following figure shows:
Ambient air diffuses into the sampling tube in a controlled
manner. BTX are absorbed on the activated charcoal and desorbed
by carbon disulphide in the laboratory and analysed by gaschromatography.
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Diagram
Comparison of ORSA diffusion tube with active
measurement in North-Rhein Westfalia [1]
Specifications
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Samplingrate
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6.44
ml/min at 20oC
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Working range
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0.5
— 50 µg/m3
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Sampling time
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2
— 4 weeks
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Detection limit
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0.2
µg/m3 for a sampling time of 1 month
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| External
influences: |
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wind
speed
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influence
of wind speed < 10% up to 4.5 m/sec
using protection shelters |
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temperature
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no
influence between 10 to 30oC |
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humidity
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no
influence between 20 to 80%
caution under tropical conditions |
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Storage
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before
use: 12 months
after exposure: 6 months
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Cross sensitivity
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Selective
method
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Expanded uncertainty*
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23.0
% at concentration levels of 1 - 5 µg/m3
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*according to GUM;
subject to change without notice |
revised 3.1.2010
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