• ECH Closed Loop Technique for ppm water in oil determination (new revisions to ASTM D6304)

Analytical Instrumentation

ECH Closed Loop Technique for ppm water in oil determination (new revisions to ASTM D6304)

Apr 20 2021

The Aqua 40 Vario and the Aquamax KF Pro Oil from ECH Elektrochemie Halle have re-defined oven and oil evaporation techniques in coulometric Karl Fischer titration. Using the new Closed Loop carrier gas technique ECH analysers can now measure over 1,000 samples in one charge of coulometric Karl Fischer reagent whilst eliminating the need for external carrier gas systems.

The traditional method of analysing ppm level water in solids, viscous and problematic liquid samples is to use a headspace oven or evaporator that is connected to a coulometric Karl Fischer titration vessel. Along with an oven, an external carrier gas is also required, in most cases, people use a nitrogen gas generator or have a separate gas cylinder connected. This “open” system can cause a significant ingress of atmospheric moisture causing high background drifts and uncertain results. Additionally, the opening of the system causes methanol evaporation from the Karl Fischer reagent which subsequently shortens the lifespan of the reagent. At ECH, we have developed a unique “Closed Loop” system whereby the oven and Karl Fischer titration cell are connected via tubing and a peristaltic pump. During the pre-conditioning/pre-titration phase, the ambient air within the oven/tubing is circulated into measuring vessel and through Karl Fischer reagent, subsequently drying the ambient air. After a short preconditioning phase, the instrument reaches a stable low end point having titrated all atmospheric water within the oven, tubing, and titration cell. In turn, creating an internal dry carrier gas.

There are several benefits to using an ECH coulometer with the Closed Loop feature:

  • Small footprint and lower cost (oven directly attached to titrator and no requirement for a gas generator or external gas supply).
  • Closed loop technique means zero atmospheric interference (more stable drift and quicker pre-conditioning times).
  • Longer reagent lifetime thanks to the titration vessel only having the sample moisture introduced, not the entire sample. When analysing low ppm water, it is possible to analyse up to 1000 samples in between reagent replenishment. 

Revisions to ASTM D6304 have implemented the technique and allow for a dry carrier gas to be used in coulometric titration, meaning the entire Aquamax KF and Aqua 40 titration range conform fully to ASTM D6304.

For further information, or to book a live product demonstration in the new ECH Studio please contact by email or visit ECH website and submit your contact form.

Read more about how ECH have improved efficiency when determining ppm water in used oils using the Aqua 40 Vario automated coulometer.


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