Page 374 - Academic Press Encyclopedia of Physical Science and Technology 3rd Analytical Chemistry

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Encyclopedia of Physical Science and Technology EN0011A-541 July 25, 2001 17:27

Organic Chemistry, Compound Detection 477

TABLE IV Detection Reagents for Different Functional Groups
Compound class Reagent Color
Alcohols Ceric ammonium sulfate Brown spots on yellow background
Aldehydes 2,4-Dinitrophenylhydrazine Yellow to red spots on pale orange background
Ketones Dragendorff–Munier modification reagent Orange spots
Alkaloids Iodoplatinate Basic drugs yield blue or blue-violet spots
Amides Hydroxylamine–ferric nitrate Various colors on white background
Amines and amino acids Ninhydrin Yellow-pink-red or violet spots on white background
Carbohydrates p-Anisaldehyde Blue-green and violet spots
Carboxylic acids Cresol green Yellow color on blue background
Bases Cresol green Blue spots on green background
Chlorinated hydrocarbons and Silver nitrate Gray spots on colorless background
chlorine containing particles
Ethanolamines Benzoquinone Red spots on pale background
Heterocyclic oxygen compounds Aluminum chloride Flavonoids produce yellow fluorescent spots
Hydrocarbons Tetracyanoethylene Aromatic hydrocarbons yield various colors
Hydroxamic acids Ferric chloride Red spots on colored background
Indoles Ehrlich reagent Indoles: purple. Hydroxy-indoles blue
Feroxides Ferrous thiocyanate Red-brown spots on pale background
Phenols 4-Amino antipyrine Red, orange, or pink spots on pale background
Polynuclear aromatic hydrocarbons Formaldehyde–sulfuric acid Various colors on white background
Steroids p-Toluenesulfonic acid Fluorescence
Steroid glycosides Trichloroacetic acid–chloramine T Digitalis glycosides: blue spots
Terpenes Diphenyl-phenyl-hydrazyl Yellow spots on purple background
Vitamins Iodine-starch Ascorbic acid; white on blue background

or sublimation. The emerging vapors are deposited as a layers according to the degree of unsaturation. The sep-
spot on the TLC-plate which is then chromatographed in arated fractions are eluted and the products subjected to
the usual way. The spot can also be scraped off, extracted GLC separation. Furthermore, the resolved methyl esters
and analyzed by GLC. may be treated to reductive ozonolysis and the result-
This technique is useful in the fields of drugs, phy- ing fragments analyzed by GC, thus furnishing important
tochemistry, food additives, and other natural and syn- structural information.
thetic organic compounds. Many organic constituents of
drug-containing plants were detected by this technique.
2. GC–TLC
Examples are constituents of essential oils, purines (e.g.,
caffeine), narcotics from drugs or tobacco, marijuana con- A recent application of the combination of TLC with GLC
stituents, mescaline from Mexican narcotic fungi, organic has been the direct application of the compounds to the
contituents of fossil fuels, and oil-shales. thin-layer plate as they emerge from the exit tube of the
gas chromatographic apparatus.
E. Coupled TLC Techniques It should be pointed out that GLC separates accord-
ing to the relative volatility, and TLC separates according
1. TLC–GC to the functional groups present. A coupling device was
constructed in which the thin layer plate is moved logarith-
There are a number of ways in which TLC can be com-
bined to advantage with GLC. The spots obtained from mically with time, while the gas chromatogram operates
TLC may be eluted, concentrated, and then subjected to under isothermal conditions.
GLC analysis. This method has been used in the analyses
of lipids, steroids, alcohols, fatty acids, esters, glycerides,
3. In Situ Chemical Reactions on TL Plates
hydrocarbons, essential oils, and many other natural and
synthetic organic compounds. Methyl esters of fatty acids In order to detect and identify minute quantities of organic
are first separated on silver-nitrate-impregnated silica gel compounds the sample is spotted on a plate which is then