Membrane Technology, Automated Water Analysis

Gas phase extraction

The gas phase extraction system (707-00) is a novel device Wasson-ECE has developed to perform water analysis. The device is a dual chamber disk. The two halves of the disk are separated by a proprietary semi-permeable membrane. The supply side has water flowing at a constant temperature and rate. Analytes that are trapped in the aqueous phase pass through the membrane into the gas extraction half of the device. Sweep gas is passed over the gas phase portion of the membrane. Analytes are collected and transferred to the gas chromatograph.

Gas Phase Extraction System

Extraction system

A nice feature of the membrane material is that organic species have a very high affinity for it. Concentration of the analytes occurs naturally on the membrane due to the material composition. This allows for excellent detection limits without further concentration. If concentration is required, a cryo trap can be used downstream of the gas phase side of the device.

Automated Water Analysis

Automated analysis diagram
  1. The Sample Source – This may be the feed line to cooling tower, a supply to a biodigestion pond, a river, a municipal water supply, etc.
  2. The filter system – The raw water sample will require some filtration prior to sampling. The amount of filtration required depends upon the sample. Therefore the filter system must be custom designed along with the rest of the on-line analyzer. The advantage of the gas phase extraction system is that the filtering requirements are less than those required by other techniques.
  3. The Sample system – In our older systems this would traditionally be a sparge and trap device. A majority of water analysis systems can now use the gas phase extraction device (application 707-00).
  4. Dedicated GC Application – The GC will be configured turnkey to perform the customer’s analysis. This may require valving for sampling, trapping and desorbing, and specialized detectors.
  5. Data Analysis – ChemStation
  6. Report Output – Most automated systems will require custom output to a control system. These include digital protocols (MODBUS), analog (4-20 mA), custom Ethernet, modem based systems, digital scoreboards (Korea), or automatic paging systems.

Uni-strut Mounted Sample System Box

Sample system box

Gas Phase Extraction vs.Other Technologies

Extraction system

Direct Injection

  • No Column Damage from Water Matrix
  • No clogging from particulates
  • Analytes are concentrated

Sparge and Trap

  • No problems from foaming agents in samples
  • Components that form azeotropes with water can be concentrated