Karl Fischer Titration and calibration using water standards.
“Calibrating” a Karl Fischer titrator is somewhat of a misnomer. What most operators are attempting to do is determine whether their Karl Fisher titrator is measuring moisture accurately.
A simple method is to run a water standard through the Karl Fischer Titrator like a normal direct injection test. Depending on the water standard you use, the result should equal a pre-determined level of moisture plus or minus a margin for error. These water standards are certified by the manufacturer (a certificate is included) to equal a precise level of moisture.
We use Hydranal water standards. There are two kinds we typically use for coulometric Karl Fischer Titrators.
1) 0.1 normal
2) 1.0 normal.
The 0.1 normal administered at about 1mL should result in 100ppm (Parts Per Million) of moisture when measured. The acceptable result for this standard for the Karl Fischer titrator is +/- 10%. So your Karl Fischer Titrator should produce a reading between 90ppm and 110ppm to be in the acceptable range. If it is, you know your Karl Fischer Titrator is performing correctly.
For the 1.0 normal everything is the same except the standard should result in 1,000ppm and your acceptable range is smaller at +/-3%. So your Karl Fischer Titrator should produce a reading between 970ppm and 1,030ppm.
I found this great video on Sigma Aldrich’s site that shows this process (it also goes into some additional detail for conducting a water standard test). To see it go to:
Hope this helps.
H.
