Factors that influence the concentration of a Karl Fischer titrant.

The concentration of the Karl Fischer titrant decreases over the time. What affects the concentration of a Karl Fischer titrant solution?

Possible reasons:

The capacity of drying agent (usually molecular sieve) to absorb ambient water is exhausted. The titrant bottle is not sufficiently sealed which leads to absorption of ambient moisture due to the hygroscopic nature of anhydrous methanol or ethanol. Moisture uptake leads to a reduction of the titrant concentration. Due to the high expansion coefficient of a Karl Fischer titrant solution, temperature fluctuations negatively affect the titrant concentration. Increasing temperature causes considerable volume increase and therefore a drop in the concentration.

Recommendations:

Check the O-ring seals periodically, at least after every change of the titrant bottle. If the O-ring seals appear to be brittle or strongly squeezed, replace them against new ones. Exchange the drying agent against fresh one on a monthly basis. If molecular sieve is used as the drying agent you may regenerate it by drying it at 200 °C (please cross check temperature with the current KF application literature) in an oven for at least 24 hours. Avoid temperature fluctuation and direct sun exposure of the Karl Fischer titrant. Keep the titrant container tightly sealed, always use fresh desiccant for titration, Store the KF titrant bottle in a cool (+15 °C to 25 °C), ventilated place.