Hanna Instruments HI 904 - Manual (Page 123)

9-11
METHODS OPTIMIZATION
The heating temperature is sample specific and can be found in applicable standard methods.
The temperatures are chosen to be as high as possible without decomposing the sample,
which can result in contamination of the titration vessel.
9.3 Karl Fischer Reagent System
A wide variety of Karl Fischer reagents exist on the market today, each designed and formulated
for specific sample matrices and titration conditions.
Coulometric Karl Fischer reagent systems consist of an anolyte and a catholyte. Reagents for
diaphragm-less generators are single-reagent systems. The reagent manufacturer will specify
if a specific reagent is suitable for cells with diaphragm or without diaphragm (or both). For
reagents requiring a diaphragm, the manufacturer will also supply a suitable catholyte.
Commercial reagents are typically formulated for one of the following applications:
- General Purpose
- Ethanol-based
- Ketone/Aldehyde
- Oil/Hydrocarbons
Consult a Standard Method or reagent manufacturer for appropriate reagents for an application.
9.3.1 Water Standards
Water standards are used to verify the titrator’s performance and analyst technique. Water
standards are an integral part of ISO 9000, GMP, GLP and FDA guidelines for water
determination.
Water standards are available commercially in single-use sealed ampoules. Concentration
values are typically 0.1, 1.0, and 10.0 mg/g and are certified by the manufacturer. Coulometry
is an absolute method that does not require calibration or titer determination, but it is useful
to occasionaly titrate water standards as a system check. This will confirm that there are no
issues with the method settings, reagents, sample addition technique, or the titrator electronics.
General procedure using a liquid water standard (ampoule):
1. Setup titrator according to the instruction manual. Ensure the titrator is set up with
the same reagent, working conditions, temperature and titrator settings to be used
for subsequent sample analyses.
2. Select an appropriate standard that closely matches the sample’s water content.
3. Break open an ampule of standard. Rinse a syringe with a small portion of standard.
4. Draw up the remainder of the standard into the syringe, weigh and titrate about
one-third of the standard in the syringe.
5. Conduct two more titrations with the standard remaining in the syringe.
6. Review the set of results on the ‘average results’ statistics screen. The average
standard concentration should be within the range specified on the Certificate of
Analysis provided by the manufacturer. There should not be excessive variability
between each result.