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02 / 2003
KF_11_03_e
The determination of water in glucose and lactose
The main principle
The release of water from different types of sugars can be compared by using the KarlFischer-Titration coupled with complete heating technology. A temperature program allows
complete desorption of bounded water. The released water is transported into the measuring
cell of the AQUA 40.00 by means of the extraction gas located in the circulation and then
immediately titrated.
Results
The following example, an analysis of lactose monohydrate, shows that by using the
complete heating technology, one can differ among surface water, water of crystallization
and water resulting from decomposition. Water released within the temperature range of
100 - 180° C corresponds to the water of crystallization from lactose monohydrate.
If water is added to the lactose, i.e., the sample is exposed to water vapour, one can make
out that the water adsorbed at the surface has already been released at 60° C. If the sample
is exposed to moisture-laden air for a longer period of time, the amount of surface water will
increase on the scale, but the temperature of the complete drying at release will not be
affected.
The determination of water in lactose monohydrate after exposure to water vapour; temperature programmed heating
procedure, increasing by 2° C/min
1/2
Developed by: ECH Elektrochemie Halle GmbH, Weinbergweg 23, D-06120 Halle/S.
Telefon: 0345/5583-711, Telefax: 0345/5583-710, internet: http://www.ech.de, e-mail: [email protected]
02 / 2003
KF_11_03_e
Similar trials with glucose show that when exposed to moisture-laden air for a longer
period of time, the water adsorbed at the surface is slowly chemisorbed as crystalline
water. This can be observed in the scheme below showing that an increase in water
content (longer exposure) creates two noticeably different graph lines.
Thus, by using the Karl-Fischer-Titration combined with the heating procedure of
sample, kinetic data can be calculated.
The determination of water in glucose according to different exposure times to moisture-laden air; temperature programmed
heating procedure, increasing by 2°/min
Conclusion
It is possible to characterize different bonding types of water in sugar by using the
temperature programmed complete cure of the AQUA 40.00. Free water adsorbed at the
surface, as well as bonded crystalline water can be found.
Measurement technology
• Karl-Fischer-Titrator AQUA 40.00 equipped with a Head-Space-Module or a heating
chamber for solids
• optional accessory: autosampler
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Developed by: ECH Elektrochemie Halle GmbH, Weinbergweg 23, D-06120 Halle/S.
Telefon: 0345/5583-711, Telefax: 0345/5583-710, internet: http://www.ech.de, e-mail: [email protected]