Development of Karl Fischer Reagents

II-1 Organic Compounds
110
Note: An error will occur at the rate of 0.3ppm of water for every 1ppm
of sulfur in the mercaptan. If the mercaptan content is low, an
accurate measurement of the moisture content can be obtained
by adjusting the measurement value.
Reference: JISK2275 Crude oil and petroleum products - Determination of
water content
Test Examples
Sample
Ethyl mercaptan
Isopropyl mercaptan
Butyl mercaptan
Isoamyl mercaptan
Hexyl mercaptan
Heptyl mercaptan
Benzyl mercaptan
Thiophenol
2-Thionaphthol
Thioglycollic acid
Moisture
(%)
0.70
0.90
0.85
0.40
0.15
0.70
0.25
0.25
0.05
3.85
6.30
6.30
3.05
2.85
1.85
4.60
2.80
-
1.35
6.95
6.35
6.25
3.05
2.90
1.85
4.60
2.80
-
1.35
7.00
Other Substances that Cause Interference
It may not be possible to obtain a clear end point with thiourea as it reacts
with iodine. This is because thiourea triggers tautomerism and interconverts
to isothiourea, which causes the same reaction as mercaptan.
NH2 NH2
S=C
�
HSC
�
NH2 NH
content (%)
Added moisture Observed moisture(%)