MXMF.Users.Handbook.V2.20.doc
LIT:MXUHB April 2003
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2. Method of measurement
How moisture content is measured with a moisture analyzer
Moisture content can be measured by heating method, Karl Fischer method, Dielectric
?
Infrared absorption
method, neutron analyzer or crystal oscillation method, among which mainly heating and drying method or
Karl Fischer method is utilized in many laboratories. Infrared absorption method and Dielectric method are
suitable for process.
Heating method is a method where moisture content is rendered by the weight of
water evaporated from ground solid or liquid samples after heating the sample for a period of time at or
over the sample’s perspiration temperature. Weight loss occurs as samples get heated and finally
converge on a certain value. Sample may pyrolyze and vaporize depending on its characteristics, which
suggests that what is vaporized is not necessarily water. However suitable sample size and heating
temperature such as temperature setting, heating time and so forth can lead a result comparable to the
one determined by Karl Fischer method.
Among all, moisture analyzers employed with heating method is easy to handle with its good operability
and clear formula of operation, low profile and can be run and maintained at a low cost, which contribute to
attracting a wide range of users who test many kinds of samples. Measurement range is from 0.01% or
0.1% to 100% and so samples even with almost 100% moisture content can be correctly and easily
measured. Heating method moisture analyzers utilizes halogen, infrared lamp, sheathed heater or micro
wave heater as heating source to heat sample on an electric balance that weighs the sample before and
after the heating to determine the moisture loss. The electric balance then needs technology that insulates
heat to the load sensor and prevents temperature drift since temperature can get over 150 – 200? . Karl
Fischer method is a method where moisture content is measured by electric chemical titration under favor
of the characteristics that in the presence of methyl alcohol, KF reagent including iodine, hydrogen
disulfide, pyridine responds specifically with water.
H
2
O + I
2
+SO
2
+3RN+CH
3
OH
?
2RN
?
HI+RN
?
HSO
4
CH
3
(anhydrate)
Water (reagent)
KF reagent
methyl alcohol
(
RN: base
?
I: Iodine
?
SO
2
: hydrogen disulfide
)
