问题：TLC stains and preparation
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提问：welly
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时间：2005-02-26 17:13:45 编辑加入/取消收藏订制/取消短消息举报该贴

Iodine

The plate can be stained with iodine. This can be achieved rapidly, by shaking the plate in a bottle containing silica and a few crystals of iodine. The iodine will stain any compound that reacts with it and so is especially good for visualizing unsaturated compounds. Most spots show up within a few seconds, but the stain is not usually permanent.

UV light

The plate can be viewed under a ultraviolet lamp to show any uv-active spots.

Dipping Solutions:

The plate can be treated with one of the reagents listed below and then heated to stain the spots. The reagent can be sprayed onto the plates, but this technique is quite hazardous and it is more effective for them to be dipped in the reagent. To do this, first let the tlc solvent evaporate, then holding the edge of the plate with tweezers, immerse the plate as completely as possible in the stain and remove it quickly. Rest the edge of the plate on a paper towel to absorb the excess stain before heating carefully on a hot plate or with a heat gun, until the spots show. This method is always permanent and should be done last. When glass plates are used the spots can sometimes be seen more clearly from the glass side of the plate.

p-Anisaldehyde

Preparation: anisaldehyde (15 g) in ethanol (250 ml) + conc. sulfuric acid (2.5 ml).
Good general reagent, gives a range of colors.

p-Anisaldehyde

Preparation: anisaldehyde:HClO4:acetone:water (1:10:20:80).
Spray plates and heat with heat gun until spots appear.
Terpenes, cineoles, withanolides, acronycine, etc..

Bromocresol green: carboxylic acids
Preparation: 0.3% in 1:4 water-methanol
add 8 drops of 30% NaOH/100 mL
carboxylic acids stain yellow-green on a blue background. (Provided by Dr. Bill Stevens)

Ceric Ammonium Sulfate Spray
Preparation: 1% cerium (IV) ammonium sulfate (CAS) in 50% phosphoric acid.
Vinca alkaloids (Aspidospermas).

Ceric Sulfate
Preparation: 15% aqueous sulfuric acid saturated with ceric sulfate.
Fairly general, gives a range of colors.

Distilled Water Spray

Spots turn translucent or opaque while background of plates turns clear.

DNP

Preparation: 2,4-dinitrophenylhydrazine (12 g) + conc. sulfuric acid (60 ml) + water (80 ml) + ethanol (200 ml).
Mainly for aldehydes and ketones, gives orange spots.

Dragendorff Reagent
Preparation: Solution A: 1.7 g basic bismuth nitrate in 100 ml water/acetic acid (4:1). Solution B: 40 g potassium iodide in 100 ml of water. Mix reagents together as follows: 5 ml A + 5 ml B + 20 ml acetic acid + 70 ml water. Spray plates, orange spots develop. Spots intensify if sprayed later with HCl, or 50% water-phosphoric acid.
Good for phenols.

Ferric Chloride Spray

Preparation: 1% Ferric (III) Chloride in Methanol/water (1:1).
Good for phenols.

Ninhydrin

Preparation:
200 mg ninhydrin
95 ml butanol
5 ml 10% AcOH
Comments:
Good for amines. Thanks to Dr. Bill Stevens (U of Minnesota) for providing this recipe.

PDAB-NaNO2 Reagent - Ehrlichs, Van Urks
Preparation: Solution A: 0.1%p-dimethylaminobenzaldehyde (PDA in conc. HCl.
Solution B: 0.1% NaNO2 (nitrite) in water. Spray plates with PDAB (solution A) first - warm -heat gun, then spray with NaNO2.
Indoles give blue colors if the 2-position of the indole ring is unsubstituted.

Permanganate

Preparation: potassium permanganate (3 g) + potassium carbonate (20 g) + 5% aqueous, NaOH (5 ml) + water (300 ml).
Mainly for unsaturated compounds and alcohols, gives yellow spots.

PMA

Preparation: phosphomolybdic acid (12 g)( in ethanol (250 ml).
Good general reagent, gives blue-green spots.

Sulfanilic Acid Reagent (Diazotized), Pauly's Reagent
Preparation:
Solution A: 0.5% sulfanilic acid in 2% HCl.
Solution B: 0.5% NaNO2 (nitrite) in water
Solution C: 0.5% NaOH in 50% ethanol
Mix equal volumes of A and B and spray TLC plates. Warm sprayed plate with a heat gun if necessary. Spray plates with solution C.
phenolic compounds turn orange or yellow with this reagent.

Sulfuric Acid

Preparation: 5% sulfuric acid in methanol.
This reagent is usually sprayed on the TLC.

Vanillin

Preparation: vanillin (15 g) in ethanol (250 ml) + conc. sulfuric acid (2.5 ml).
Good general reagent, gives a range of colors.

回复人：admin,★ (论坛管理员-欢迎大家访问化学化工论坛) 时间：2005-02-26 17:31:56 编辑	1楼
http://ccebbs.com/forum/dispq.asp?lid=719

回复人：welly,▲ (做有机合成，希望能和大家交流！) 时间：2005-02-26 21:29:13 编辑	2楼
不好意思，没仔细搜索论坛！！

回复人：hrwen,▲▲ (从事有机合成) 时间：2005-03-07 09:18:23 编辑	3楼
好东西

回复人：rph,▲ () 时间：2005-03-17 20:56:24 编辑	4楼
不错。

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