Thin-Layer Chromatography

80
3 Chemical Methods oj Detection
IE
11000
9000-
7000-
5000-
3000-
1000-
0
streaks 0 1 2 3
ng/Spot
IE
11000-
9000-
7000-
5000-
3000-
1000-
0
1 2 3 U
ng/Spot——
Fig. 38: Comparison of manual dipping (A) with mechanized dipping (B) on the basis of
scans and calibration curves [114] — 1 = m-diethylstilbestrol, 2 = rra/w-diethylstilbestrol,
3 = ethinylestradiol Scanning curve 2 ng of each substance per chromatogram zone /esc =
313 nm, /n > 390 nm Dipping solution water - sulfunc acid - methanol (85+15 + 1)
I
glass sprayer was normally employed (Fig. 39A), which was connected to a pressure
supply (membrane pump) or cyhnder of inert gas It was necessary to use a jet
so fine adjusted that it was possible to spray the reagent solution homogeneously
Spraying was earned out at a pressure of 0.6 to 0.8 bar from a distance of 20 to
30 cm in a suitable fume cupboard (Fig. 37) According to WALDI the spray should
be applied in a meandenng pattern with the return point of the spray outside the
track of the chromatogram (Fig 39B) [115]
Fig. 39: All glass sprayer (A), spray pattern (B)
The same applies to the use of spray pistols (spray guns and aerosol cans), the
frequency of whose use ought probably to be reduced on account of the propellant
gas (chlorofluorohydrocarbons) employed Manual depression of the button valve
of the vertically held spray can "shoots" the propellant gas through a fine jet and
drags the sucked-up reagent solution with it onto the vertically held chromatogram
(water pump pnnciple)
Because when operated manually the spray unit can never be moved so uniformly
that the chromatogram is homogeneously covered with reagent and the amount