The most easily overlooked consumable when using a Karl Fischer moisture analyzer is the electrolyte. Many people think that if there is no significant change, they will not replace it, but once the electrolyte fails, the measured data is completely unreliable, and even worse, the results may still "look normal" and quietly give incorrect data.

What color is a normal electrolyte

The fresh Karl Fischer electrolyte is a deep reddish brown color (over iodine state). In the working state (equilibrium state), the normal color is light yellow. If the color changes to light brown or light red, the electrolyte has failed and must be replaced, and cannot continue to be used.

However, color judgment is only a preliminary visual inspection and is not 100% reliable. Electrolytes that appear to have normal colors may also have mild failure.

More accurate judgment method - Platinum Net observation

The manual provides a more reliable method:

In the state of electrolytic equilibrium, add 0.4 µ L of pure water to the electrolytic cell, reduce the stirring speed to 0, wait for 10 seconds, and then restore the stirring speed to normal. Carefully observe whether there is a large amount of dark red iodine under the platinum mesh of the electrolytic electrode.

Appearance of dark red iodine=normal electrolyte (iodine is produced by electrolysis and has not yet fully reacted with water)

No dark red iodine appears, indicating that the electrolyte has failed (iodine cannot be generated normally, indicating a decrease in electrolytic reaction ability)

The consequences of failure are more severe than imagined

After the electrolyte fails and continues to be used, iodine will adhere to the platinum mesh of the electrolysis electrode, causing the platinum mesh to change from bright white to black brown. The iodine attached to the platinum mesh is extremely difficult to remove, ultimately leading to the scrapping of the electrolytic electrode, which is a significant loss. The manual clearly states that this is a common phenomenon and requires caution.

Reference for the service life of electrolyte

Each 100mL of electrolyte can react with no less than 1g of water. If the measured sample has a high water content and the electrolyte is consumed quickly, frequent replacement is required. If a large number of bubbles are released from the electrolyte during the measurement process, or if the reproducibility of the results significantly deteriorates or the time to reach the endpoint is abnormally prolonged, it is also a signal for replacement.

0.5 grams of water can cause the failure of 500mL of electrolyte - this number indicates the sensitivity of the electrolyte to moisture. When replacing, it is necessary to ensure a dry environment and quick operation.