Thin-Layer Chromatography

ji z myswui Meinoas oj uetection
fluorescence and phosphorescence indicators. The former can be incorporated in
the adsorbent layers or applied afterwards by spraying or dipping, the latter are
always incorporated as homogeneously as possible into the stationary phase.
Fluorescence occurs primarily in organic substances and phosphorescence, on the
other hand, in inorganic compounds.
Organic fluorescence indicators for aluminium oxide, silica gel and cellulose layers
(code F366, UV366) include:
the sodium salt of 3-hydroxypyrene-5,8,10-trisulfonic acid [6],
the sodium salt of 3,5-dihydroxypyrene-8,10-disulfonic acid [7],
sodium fluorescein [8 — 11] and fluorescein [12] or 2',7'-dichlorofluorescein [13 —
19],
rhodamine B [12, 20-23] and rhodamine 6G [24-26],
morin[ll,24, 27-29],
cyanine dyestuffs [30, 31],
stilbene derivatives (e.g. diaminostilbenetriazine) [12, 32] and
optical brighteners (Ultraphor WT BASF [12, 33], Calcofluor R-white [34],
Leukophor).
Oxytetracycline can also be employed at low pH on calcium-containing layers [35].
The scintillators are a special type of fluorescence indicators; they are employed
for the fluorimetric detection of radioactively labelled substances. They are stimulated
by /^-radiation to the emission of electromagnetic radiation and will be
discussed in Volume 2.
The substances employed as inorganic phosphorescence indicators (incorrectly referred
to as fluorescence indicators) include blue (tin-activated strontium compounds),
yellow (uranyl acetate [36]) and yellow-green (manganese-activated zinc
silicate [37] or zinc cadmium sulfide [38]) emitting substances (code F254, UV254).
Pigment ZS-super (RIEDEL DE HAEN) has also been employed [81]. Since these are
not acid-stable they are replaced by substances such as alkaline earth metal
tungstates in RP phases (code F254S). These possess a pale blue emission [39].
The advantages of these inorganic indicators are:
• Such indicators do not migrate during chromatography to the solvent front
under the influence of either polar or nonpolar organic solvents (uranyl acetate
is an exception).
Fig. 6: UVIS and MinUVIS analysis lamps (DESAGA).
z.z ueieciwn oj Aosoromg zuosiances