ADC 2
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 reated 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). Humidities larger than 70%
are producing irreversible reactions in the binder and should be
avoided.
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
Relative Humidity
Ad
so
rp
ti
o
n
[W
ei
g
h
t%
, n
o
rm
. KG T
y
p
100]
Typ 100
Typ 60
Typ 40
Fig.19: Humidity adsorption of different silica gel.
Manual, August 2005
Page 39
Содержание ADC 2
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