Hanna Instruments HI 903, Quick Start Manual

Page: 142 / 220

9-14
METHODS OPTIMIZATION
6. Facilitate extraction by shaking the solution or placing the solution on a stirring
plate or in a sonicator.
7. Allow the insoluble portion of the sample to settle to the bottom of the extraction
bottle.
8. Titrate an appropriately sized sample of the supernatant (solvent above the settled
solid sample).
9.2.5.5 Homogenization
Homogenization is recommended for non-aqueous or mixed phase liquid samples as well as
solids with inhomogeneous distributions of water. Water can be evenly distributed throughout
a collected sample by the use of high speed, high shear mixers called homogenizers.
In mixed phase (oil and water) non-aqueous samples, water tends migrate to the surface of
the sample solution, adhere to the inner walls of or sink to the bottom of the sample bottle.
This is particularly problematic when sampling is done at high temperatures and the specimen
is subsequently allowed to cool to room temperature prior to analysis.
Solid samples typically exhibit inhomogeneous water distributions and must therefore be
thoroughly reduced to powder or homogenized. The procedure for homogenization depends
upon the characteristics of the specific sample.
Homogenization is particularly suited for semi-solid samples and suspensions and is the only
method that can disrupt plant and tissue cells in order to release water present inside the
cells. Homogenization is typically carried out externally in a dry flask with the addition of a
suitable solvent, preferably methanol.
9.2.5.6 Heating
Sample heating is used for the analysis of solid or liquid samples that cannot be extracted or
that interfere with the Karl Fischer reaction. These include plastics, minerals, petrochemical
products which contain additives, and starting materials for pharmaceutical products.
Samples are heated in a special oven while a dry stream of carrier gas passes through the
sample chamber or, for liquid samples, the sample itself. The carrier gas is introduced into
the titration vessel.
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.