Coulometric Titration

Advantages of coulometric titration:

• Easy to use
• Detects low concentrations of water
• High accuracy

Product range HYDRANAL^® coulometric reagents

Composition
Coulometric Karl Fischer titrations usually require two reagent solutions: an anolyte (solution in the anodic compartment) and a catholyte (solution in the cathodic compartment). HYDRANAL^®-Coulomat A type reagents are used as the anolyte. They contain iodide and a sulfur dioxide/imidazole buffer in a suitable solvent. HYDRANAL^®-Coulomat CG reagents are used as catholytes. The non-toxic HYDRANAL^®-Coulomat E is used as both anolyte and catholyte; it is based on ethanol and does not require hazardous labeling.

Toxicity
Except for HYDRANAL^®-Coulomat AK containing 2-methoxyethanol, all HYDRANAL^®-Coulomat reagents are free of toxic and noxious compounds, such as pyridine, carbon tetrachloride and 2-methoxyethanol. In most reagents, methanol is the most hazardous component, and it can be eliminated by using HYDRANAL^®-Coulomat E where ethanol replaces methanol.

Stability
When unopened, most HYDRANAL^®-Coulomat reagents have a shelf life of at least five years.


Using HYDRANAL^®-Coulomat Reagents
The following procedure is generally used for the coulometric determination of water (Figure 2.3):

1. Fill the anodic compartment with HYDRANAL^®-Coulomat A/AG/AD/AG-H/AG-Oven/AK/E
2. Fill the cathodic compartment with HYDRANAL^®-Coulomat CG/CG-K/E
3. Titrate the cell to dryness
4. Add sample
5. Titrate the water content

Figure 2.3: Coulometric titration with HYDRANAL^® -Coulomat reagents.


Coulometry without Diaphragm
Coulometric titration cells are also available without diaphragm. They comprise only one compartment and require only one reagent. HYDRANAL^®-Coulomat E, AD, AG, AG-H, AG Oven and AK can be used with diaphragm-less cells. To use these reagents, follow the general procedure for coulometric determination of water without the use of a catholyte solution.

• Volumetric titration using one-component reagents
• Volumetric titration using two-component reagents

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