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Material Harvest® TLC plates
In relation to thin layer chromatography (TLC), Material Harvest is a supplier of:
Material Harvest® analytical TLC plates (glass-backed silica gel 60 with F254 indicator)
Material Harvest® preparative TLC plates (glass-backed silica gel 60 with F254 indicator)
SiliaPlate® functionalised silica gel TLC plates (glass-backed silica with F254 indicator)
Bulk silica gel for the fabrication of TLC plates (with fluorescent indicator + gypsum)
We offer academic and volume-based discounts - please contact us for details.
Notes on analytical and preparative TLC
Thin layer chromatography (TLC) is a chromatographic technique used to separate mixtures of non-volatile compounds. It is employed by synthetic chemists to achieve the following:
TLC plates comprise a sheet of adsorbent coated over a substrate. The adsorbent can be any stationary phase including silica gel, Florisil®, reverse phase silica or an exotic functionalised silica gel. The most common substrates include glass, aluminium foil and some plastics.
The adsorbent is normally mixed with an inert binder such as calcium sulphate (gypsum) and water, so as to assist binding to the substrate. Such plates must be dried and activated by heating in an oven before they are ready to use. The thickness of the adsorbent layer is normally in the range of 0.1 - 0.25 mm in analytical TLC. In the case of preparative TLC, where the chemist seeks to isolate the compounds, adsorbent thickness values are in the range of 0.5 - 2.0 mm.
Instructions for running a TLC experiment
A "spot" of the solution containing a compound or a mixture of compounds is applied directly on the adsorbent, approximately 1 - 2 cm from the bottom of the plate. The solvent is allowed to evaporate, usually with gentle heating (this can be achieved by use of a heat gun or by baking the plate directly on a laboratory hotplate).
A small amount of an appropriate solvent (known as the eluent) is poured into a suitable container (known as the chamber) such as a glass beaker. The depth of the solvent must be such that if the TLC plate were to stand inside the chamber, the above-mentioned spot would not be immersed in the solvent. A strip of filter paper is then placed inside the chamber - this filter paper must be tall enough to almost reach the top of the container.
The solvent is allowed to rise up the filter paper and the chamber is sealed, thus allowing the atmosphere inside the chamber to become saturated. This is a very important step because failure to saturate the atmosphere will result in poor separation and non-reproducible results. To seal the chamber, a sheet of glass or a watch-glass can be employed.
The TLC plate is then positioned inside the chamber and the eluent is allowed to move up the adsorbent via capillary action. When the solvent front reaches no higher than the top of the filter paper in the chamber, the plate should be removed and the solvent front marked on the adsorbent using a pencil. The plate is then dried and visualised using UV light and/or TLC dips for chemical enhancement.
TLC Dips for chemical enhancement
TLC stains are commonly used alongside UV enhancement to visualise compounds. This is because chemical enhancement can often distinguish compounds that cannot be seen under UV light - for example, a potassium permanganate dip can be used to identify non-UV active alcohols and other compounds prone to permanganate oxidation.
The following TLC dips should be prepared by qualified personnel and only after a safety or risk assessment has been carried out.
1) Ammonium Molybdate
Good general reagent for chemical enhancement. It requires heat to visualise spots, giving deep blue spots against a pale background.
Preparation: Ammonium molybdate (5 g) and ceric sulphate (0.2 g) dissolved in 5% aqueous sulphuric acid (100 ml).
Good general reagent; it requires heat to visualise spots, giving blue/purple spots against a pink/purple background.
Preparation: Anisaldehyde (15 g) dissolved in ethanol (250 ml), to which conc. sulphuric acid (2.5 ml) is added.
3) Ceric Sulphate
Good general reagent; it requires heat to visualise spots.
Preparation: Ceric sulphate added to 15% aqueous sulphuric acid until saturation.
4) 2,4-Dinitrophenyl Hydrazine
Great reagent for aldehydes and ketones. It gives red and yellow spots against an orange background.
Preparation: 2,4-Dinitrophenyl hydrazine (12 g) dissolved in a mixture of conc. sulphuric acid (60 ml), water (80 ml) and ethanol (200 ml).
5) Dragendorff's reagent
Good for nitrogen-containing compounds. It gives orange spots on an orange background.
Preparation: A first solution containing basic bismuth nitrate (0.17 g) in acetic acid (2 ml) and water (8 ml) is prepared. A second solution containing potassium iodide (4 g) in acetic acid (10 ml) and water (20 ml) is also prepared. The two solutions are mixed together and diluted to a total volume of 100 ml by adding water.
Good reagent for unsaturated compounds. It gives brown spots and is reversible, therefore it is compatible with preparative TLC. To reverse, the TLC plates must be gently heated until the iodine has sublimed.
Preparation: The TLC plate is positioned in a sealed container that houses silica powder and iodine crystals.
Very useful reagent for amino acids and amines. It requires heat to visualise, giving spots that range from blue/purple to brown, against a beige background.
Preparation: Acetic acid (3 ml) added to a solution of ninhydrin (0.3 g) in n-butanol (100 ml).
8) Potassium Permanganate
Excellent reagent for unsaturated compounds, alcohols and other products that are prone to permanganate oxidation. Heating may be required to visualise.
Preparation: Potassium permanganate (3 g) and potassium carbonate (20 g) dissolved in 5% aqueous sodium hydroxide (5 ml) and water (300 ml).