Coulometric Karl Fischer Titration
Coulometric Karl Fischer titration is best for finding routine low level moisture under 1% or 2%. Part Per Million (PPM) detection to 1PPM combined with a "complete" reagent setup inside the titration vessel makes testing for low level moisture very efficient.
Typically liquid samples are delivered by a syringe and needle through a septum. If however samples take the form of a gas or solid substance accessories and evaporators can be employed with a coulometric Karl Fischer titrator to obtain the moisture results. A coulometric Karl Fischer titrator can come in a simple form with very basic features like the Aquapal III. Other models like the MKC-710 series can include additional capabilities including moisture curve monitoring, data software, auto drain and fill as well as multi-instrument configurations.
In a coulometric system the reagents are referred to as a complete system meaning that all of the reagent necessary to complete a water measurement test is inside the tiration vessel. A detected electrical current (conductivity) arising from the presence of moisture in a sample will cause an electro-chemical reaction. Depending on the amount of "conductivity" detected will determine the amount of reaction and neutralization that will occur. The process of introducing a sample with moisture and having it neutralized and measured will repeat until the reagent either expires or the vessel fills to capacity.
Coulometric Karl Fischer titrators can be configured to run with just a single reagent called an anolyte or configured as a dual setup running both a anolyte and a catholyte. Some moisture tests perform better on samples when a single reagent setup is selected whereas other moisture tests perform better when a dual reagent setup is used. Sometimes trial and error on different types of samples determines which setup is best.
Water standards are also important to have on hand when working with a coulometric Karl Fischer titrator because it helps the operator run self-checks from time to time. Using pure water is not an option as the sensitivity and finite capabilities of the reagents to count H2O is impractical.