From: Ismail, Fyaz (F.M.Ismail$##$livjm.ac.uk)
Date: Thu Mar 17 2005 - 07:21:06 EST
The identification of compounds can be achieved by either spraying or dipping the plate using a number of reagents, a list of which is available in common textbooks of Organic Chemistry such as Vogel's Textbook of Organic Chemistry (various editions). A suitable choice depends on the nature of the compounds you are attempting to identify. The most general are phosphomolybdic acid (5% solution in ethanol) yields blue-green spots; Vanillin (3% solution in ethanol containing 1ml of sulfuric acid) also produces various colours. Similarly, anisaldehyde (2.5 % solution containing 1 ml of sulphuric acid) and ceric sulphate (15% aqueous sulfuric acid saturated with ceric sulfate) both produce various colours. A less satisfactory reagent is alkaline potassium permanganate that is suitable for detection of unsaturated compounds and alcohols (yellow spots) (see Advanced Practical Organic Chemistry by J. Leonard; B. Lygo and G. Procter, Blackie, Academic and Professional, Oxford, 2nd Edition, 1995). Using a glass backed plate allows one to heat the plate to a high temperature accelerating the development of the spots in question. Naturally you may scan using a densitometer to quantify your results.
If you are detecting specific types of compounds and are attempting to identify the functional Groups present, you can spray them with an appropriate reagent. A useful article is Functional Microanalysis by Chromato-Spectrometric Methods by Ya. L. Kostyukovski and D. B. Melamed: Russ. Chem. Rev, 54(2) 1985 pp 199- 213.
Dr. Fyaz M. D. Ismail,
Subject Leader,
Medicinal Chemistry,
Pharmacy and Chemistry
Liverpool John Moores University,
Liverpool L3 3AF
-----Original Message-----
From: everybody-bounces$##$orglist.net [mailto:everybody-bounces$##$orglist.net]On Behalf Of madhav balakrishna mallia
Sent: 17 March 2005 08:49
To: everybody$##$orglist.net
Subject: ORGLIST: question
hello,
TLC is the most common technique that we use for following reactions and identifying products. but there are instances when some of the reactants/reagents do not adsorb iodine or UV. do anyone know some other method than using conc. sulphuric acid spray (thus charing the compound) for identification of compounds in TLC?
Madhava B Mallia
Scientific Officer D
BHABHA ATOMIC RESEARCH CENTRE
Mumbai
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