How often will I have to exchange the microsensor?

How long a microsensor will last strongly depends on the application and the handling:
We recommend recalibrating the sensor after 25.000 measuring points, then you can continue measuring. The chemistry of the sensor itself is very stable.
However, the microsensor is fragile, since its tip is only 200 µm or even less in diameter. In case it hits solid material the tip might break. Therefore, the lifetime of the microsensor is also a matter of handling, and we recommend to use a micromanipulator when inserting the microsensor in semi-solid or solid samples.