Instruction Manual, November 2016 Page 39
6. Additional measurement values
Several approaches have been made to quantitatively measure the
effective humidity on a HPTLC plate. It has been proven that by
means of this principle for humidity control, the activity of the
plate can be controlled reproducibly. The figure below shows 4
different measurements and related transfer times from dry to
humid and vice versa. The HPTLC plates have been weighted with
a precision balance.
Fig.18: Measurement of the humidity of the HPTLC plate by weighting. It has been
shown, that within 2 – 5 minutes a stable equilibrium is reached – for the humidifying as
well as the drying process (75% rH:10 minutes). Used plate material: Merck HPTLC
plates silica gel 60 F 254.
Fig. 19 shows the values for water absorption for different silica
gels from Merck (courtesy Merck). Humidity larger than 70% is
producing irreversible reactions in the binder and should be
avoided.
Fig.19: Humidity adsorption of different silica gel.
Adsorption Isotherms for Silicagel H2O (20deg C)
0
10
20
30
40
50
60
70
80
90
100
0 10 20
30
40
50 60 70 80 90 100
Adsorption [Weight%, norm. KG Typ 100]
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Telephone
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