Development of Karl Fischer Reagents

2. Natural Products
Key Points
Substance
Silver fir leaves
Tree roots
Pollen
Pine resin
Rosin
Dehydrated
solvents
General-use
"
Sugar-type
Ketone-type
"
Sample Quantity
(g)
Chapter III: Applications - 2
Natural products vary widely and the appropriate Karl Fischer titration
should be selected to suit the particular sample. Direct titration is used
for substances that dissolve in dehydrated solvent or that are unstable
when heated. If the sample is stable when heated, use the moisture
vaporization method. The heating temperature must be considered
carefully when using that method. If the temperature is too high the
breakdown of the substance could lead to interference. (For example,
the end point may not be reached, or the analytical results that are
obtained may be abnormally high.)
Karl Fischer titration can be carried out using either volumetric or
coulometric methods, but volumetric titration is probably more suitable
since natural products tend to have a high moisture content.
[Examples of Measurement]
(1) Volumetric titration
Reagents used: Karl Fischer Reagent SS-Z (or SS)
Dehydrated Solvent GEX, KTX, SU (or MS, CM,FM) 25-50ml
Substance
Heating Temperature
( � C)
0.0462
0.0279
0.0071
1.0106
0.7388
Sample Quantity
(g)
Measurement Value
(mg)
3.12
2.53
0.64
0.74
6.15
Measurement Value
(mg)
Moisture Content
(%)
6.76
9.07
9.0
0.073
0.832
(2) Moisture vaporization - Volumetric titration
Reagents used: Karl Fischer Reagent SS-Z (or SS)
Dehydrated Solvent GEX (or MS) + PG (3:1) 50-100ml
Moisture Content
(%)
Pine resin 130 1.6708 0.83 0.050
189