Term
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Definition
o involves the movement by capillary action of a liquid phase (generally organic solvent) through a thin, uniform layer of stationary phase (usually hydrated silica gel, SiO2) held on a rigid or semi-rigid support, normally glass, aluminum or plastic sheet or ‘plate’
o relatively inexpensive and simple
o fume hood is needed to visualize analytes
o powerful qualitative method when used with sample pretreatment such as LLE
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Term
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Definition
o sample is loaded directly onto the silica gel layer
o pencil marking 2 cm from the bottom of the plate, 10 cm above the origin to indicate the optimum position of the solvent front
o sample loading- using a micropipette or syringe, no more than 5mm in diameter
o volume of solvent applied should be kept to a minimum ( 5-10µL of solution containing about 10 µg of analyte is suitable)
o applying the sample extracts before the standards minimizes the risk of cross contamination
o spot should be dried with a stream of air or nitrogen prior to chromatography
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Term
| oGlass TLC development tanks |
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Definition
| Some tanks have a well at the bottom to reduce the amount of solvent required |
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Term
| • Visualizing the Chromatogram |
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Definition
o Examine under UC light (254 and 366 nm)
o Plates can be ‘dipped’ in reagent
Unless special precautions are taken, the structure of the silica tends to be lost and the chromatogram destroyed
o Reagent is normally lightly applied as an aerosol using a commercially available spray bottom attached to a compresses air or nitrogen line
Inverting the plate before spraying helps the reagent to be sprayed evenly on plate
Plastic or aluminum-backed plates are used then the appropriate regions can be cut up and sprayed separately
o Recording system
Standardized data recording system is valuable for reference purposes- ideally a digital camera should be used and the files archived
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Term
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Definition
distance the analyte has travelled from the origin) / (Distance the solvent front has travelled from the origin)
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Term
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Definition
o Standardized TLC system that is available in kit form together with a compendium of colour plates showing Rf values, colour reactions and additional information to facilitate interpretation (AB system)
o Over 700 analytes and their metabolites have been documented for ease ID
o Problems can arise when attempting to differentiate compounds with similar mobility and colour reactions
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Term
| High-performance thin-layer chromatography |
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Definition
o HPTLC plates have a smaller average particle size (5-10µm) and give efficiently than conventional plates
o Reverse-phase plates- hydrophobic moiety is bonded to the silica matrix
o Both are expensive and have lower sample capacity than conventional plates
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Term
o HPTLC plates have a smaller average particle size (5-10µm) and give efficiently than conventional plates
o Reverse-phase plates- hydrophobic moiety is bonded to the silica matrix
o Both are expensive and have lower sample capacity than conventional plates
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Definition
o Ways to ‘driving’ the flow
Rotational planar chromatography (RPC)- centrifugal force is used
Electroplanar chromatography (EPC)- TLC equivalent of CEC
Overpressured-layer chromatography (OPLC)
• Now called Optimum performance laminar chromatography
• Can be thought of as flat-bed HPLC
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Term
| Quantitative thin-layer chromatography |
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Definition
o Can give highly reproducible results
o Radiolabelled compounds are used frequently and analytes can be located on TLC plates and removed for scintillation counting or located and quantified by radioactive scanning
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