Thin-Layer Chromatography

68 3 Chemical Methods of Detection
Table 13: (Continued)
Substances Method, reagent and end products References
Estrone, estradiol,
estnol
again into the reagent solution; dry the
chromatogram and develop it.
3.1.5 Esterification and Etherification
Dip silica gel foil 2 cm in saturated Fast Black Salt
K solution and dry in a stream of warm air. Apply
sample solution, dip again in reagent solution and
dry. Dip the TCL plate 2 cm in 4% pyridinecyclohexane
solution, dry at 100 to 200°C and
develop the azo-dyestuffs that are formed.
[294]
MILLER and KIRCHNER [9] and MATHIS and OURISSON [1] have both already
demonstrated that esterification at the start can be employed to distinguish primary,
secondary and tertiary alcohols. Tertiary alcohols react much more slowly
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Fig 33: Differentiation of primary (citronellol), secondary (menthol) and tertiary alcohols
(linalool) by in situ prechromatographic acetylation: citronellol reacts completely, menthol
partially and linalool not at all.
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td
3.1 In Situ Prechromatographic Derivatization 69
or not at all and can, thus, be separated chromatographically from the esters that
are formed (Fig. 33). Some examples are listed in Table 14. They reveal that acetic
and trifluoroacetic anhydride have been employed almost exclusively for the
esterification of alcohols, while acids have been esterified with diazomethane or
sodium methylate.
Table 14: Prechromatographic derivatization by esterification and etherification.
Substances Method, reagent and end products References
Steroid sapogenins
Aflatoxins
Aflatoxins, ochratoxin A,
stengmatocystine,
penicillic acid, patulin
Ochratoxin A, citrinin,
penicillic acid,
sterigmatocystine,
zearalenone
Menthol, citronellol,
linalool
Polyglycerol
Patulin
*-, /?-Amynn,
6-hydroxyflavones
Apply sample solution; then moisten with [62]
trifluoroacetic anhydride, dry and develop. Sapogenin
trifluoroacetates are produced.
Apply extract and standard, then apply [63, 64]
trifluoroacetic acid, allow to react at room temperature
for 5 min then dry for 10 min at a max.
of40°C and develop.
Apply sample solution and dry; then apply [65]
trifluoroacetic anhydride; allow to react at room
temperature for 45 min, develop. The derivatives
of patulin and penicillic acid possess appreciably
different hRt values.
Apply extracts of cereals or fungal cultures; apply [66]
50 nl pyridine — acetic anhydride (1 + 1) on top;
remove the excess reagent in a stream of cold air
and chromatograph. The reagents can also be applied
via gas phase
Apply the alcohols followed by the acetylation [46]
mixture on the still damp spots. Repeated application
of the reagent is necessary for complete
reaction; heat to 100°C for 15 min, then
chromatograph.
Apply sample solution; then apply 60% acetic [67]
anhydride in anhydrous pyridine, heat to 95 to
100 °C for 15 min, allow the excess reagent to
evaporate, develop.
Apply sample solution, then apply acetic anhy- [68, 69]
dride — pyridine (9 + 1), allow to react for 5 min
and dry for 15 min in a stream of warm air.
Apply sample solution as band, followed by acetic [16]
anhydride — pyridine (6 + 1), warm to 40 "C for
1.5 h in a desiccator in an atmosphere of acetic