INFICON CMS5000 Monitoring System - Manual (Page 15)

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CMS5000 Operating Manual
Chapter 1
Introduction
1.1 Introduction
WARNING
Due to U.S. Nuclear Regulatory Commission regulations,
the CMS5000 oven, which contains a sealed radioactive
source, may not be repaired by unauthorized personnel.
INFICON will provide the maintenance, repair,
replacement and disposal of the radioactive source, as
well as any part of the detector.
The CMS5000 Monitoring System provides online water or air monitoring for the
detection and analysis of VOCs. The programmable sample collection system
allows for on-site, rapid analysis of current air or water conditions without the need
for pre-treatment or filtration.
For water analysis, VOCs are purged from the water flowing through the water
vessel. Argon will bubble into the water, the gas bubbles will rise through the water
and collect at the top of the collection tube. As the bubbles rise, a portion of the
VOCs will pass from the water phase to the gas phase — this is known as
"partitioning". The ratio of the VOC concentration in the water phase, VOC
water,
to
the concentration in the gas phase, VOC
gas
, is the partition coefficient. See
equation [1].
[1]
Each compound will partition according to its solubility in water, its vapor pressure,
the specific water sampling matrix and the temperature. The quantity of VOCs
detected is dependent on the partition coefficient. In general, highly polar
compounds are more readily detected than less polar compounds.
A permeation tube that contains toluene is used as a check standard to ensure
proper system calibration and verify sample integrity. It will compensate for normal
fluctuations in the column, the concentrator and detector sensitivity. The lifetime of
the permeation tube is approximately 8 years.
After collection, the VOCs from the air or water samples are drawn into the
CMS5000 with the internal pump and adsorbed by the concentrator. The VOCs are
then desorbed into the column of the gas chromatograph by heating the
concentrator and reversing the carrier gas flow.
Partition Coefficient
VOC
water
VOC
gas
------------------------
=