Case Study VOCs analysis in water by Purge&Trap0 pages

Case Study N°AA7 – Ambient air monitoring – VOC Purge & trap – updated: 09.10.15

Case Study
Ambient Air Monitoring Applications

Analysis of VOC compounds in water by Purge & Trap
or dynamic headspace
Context & Challenges
Volatile organic compounds (VOC) can be dissolved in water. Sometimes water is polluted and to study
contamination of VOC in finished drinking water, VOC must be measured.

Chromatotec® Solutions
Chromatotec® has developed a specific system for the measurement of VOC in water: a Purge & Trap system, the
airmoPURGE. The analyzer is coupled with a degasing system allowing the extraction of dissolved gases.
The complete system is based on:
-

502.2 method from US EPA – “Volatile organic compounds in water by purge and trap capillary column gas
chromatography with photoionization and electrolytic conductivity detectors in series – Revision 2.1”.
524.2 method from US EPA – “Measurement of purgeable organic compounds in water by capillary column
gas chromatography/mass spectrometry – Revision 4.0”.

Technical information and results
A degasing system using an inert gas, nitrogen, was used to extract VOC from water. A constant volume of water
is injected into the system. Then, the extracted gases will go to the analyzer to be evaluated.
Degasing system: Purge composition
The system is designed to extract VOC dissolved in water. The different parts of the degasing system are:

A sparger to extract VOC from water
A pressure regulator to adjust the N2 inlet pressure
(extraction with 40 ml/min)
A 5 ml sampling loop
A peristaltic pump to fill up the loop
An injection valve to inject water inside the sparger
Solenoid valves
A pinch valve to evacuate water after extraction
Ultra-High Purity (UHP) Nitrogen generator (Nitroxychrom)

The consumption of water is around 25 ml/min when the peristaltic pump is turned on.

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