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Reference Standards Parts & Consumables Regulations

Effective Batch & Column method pre-treatment for AOX & TOX samples

Trace Elemental Instruments XPREP 3 is a filtration unit designed to prepare samples for both batch (AOX) and column (TOX) method. After the filtration stage, the samples are introduced in an automated halogen analyzer.

The filtration unit is equipped with three independent operating channels, which can be configured to run either batch- or column method:

  • For the batch method, a quartz frit is used to separate the water from the activated carbon after the adsorption stage. Next the reusable quartz frit is ready for introduction into the combustion zone.
  • For the column method, 2 pre-filled columns are connected, using luer-lock fittings for rapid column change or column holder for non luer-lock columns.

After filtration the halogen loaded carbon is cleared from the column into a reusable quartz sample cup, ready for introduction into the combustion zone.

How Does the Batch Method Work?
The AOX batch method is based on the adsorption of the organic halogens onto activated carbon.
A mixture of 50 mg activated carbon and 100 ml water sample is shaken for at least one hour according to the DIN, ISO and CEN regulation.
During this treatment stage, the activated carbon adsorbs the organic halogens.
Gas pressure forces the water through the quartz frit, leaving only the active carbon behind. Inorganic chlorides are removed while rinsing with a nitrate wash solution.
Once the pre-treatment is completed, the quartz frit with activated carbon is transferred into the AOX analyzer.
How Does the Column - or TOX - Method Work?
Similar to the batch method, halogens are adsorbed onto activated carbon inside a pre-packed column. Two columns are joined together, and connected to the filtration unit. Next, 100 ml sample is poured into the filtration channel. Gas pressure is applied and set to reach a 3 ml/min sample flow over the joined columns.

Organic halogens will adsorb onto the first and second column. During the washing stage, inorganic chlorides are removed using a nitrate wash solution. The carbon content of each column is emptied into a reusable quartz sample cup and transferred into the analyser.

The second column serves as a “break-through” check. If the analytical result of the second column is more than 10% of the total of both columns, the sample should be diluted and re-run. A frit may be used as particulate filter, to protect columns from “obstructing” the sample flow
  XPREP System Specifications  
  Dimensions (W x H x D) 30 x 29 x 57cm (11.8 x 11.4 x 22.4 inch)
  Weight 18kg (39lbs)
  Gas connectors 1/8" and 1/16" Swagelok
  Gases Argon or Helium (carrier gas)
  Primary pressure gas sample up to 50 bar
  Secondary samping pressure 2 - 5 bar (29 - 72 psi); adjustable
  Primary pressure liquefied gas up to 25 bar
  Secondary sampling pressure automatically controlled
  Evaporation Temperature range ambient up to 75 °C
  Sample loops 10 mL gas; 100 μL liquefied gas


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