Practical investigations
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I am doing my coursework and am doing thin layer chromatography to determine the purity of my aspirin samples. Could you tell my why I would use iodine crystals as a locating agent? 100408
Igloo writes ...
Iodine is often used as a locating agent for organic chemicals, and this particular phenomenon is certainly not limited to aspirin. The reason why it happens is that iodine vapour is adsorbed on to the surface of the aspirin molecules, and stay there for a short time trapped in the paper, making it possible for you to see where the iodine has been adsorbed. Fortunately the substance used in the thin-layer (whether this be silica or aluminium oxide) does not adsorb iodine in the same way, so where you see pale brown spots you are effectively seeing where your aspirin has got to. The process is a physical one and is totally reversible, so if you leave the plate for a short time the iodine will eventually vaporise away, and if it is once again placed in an atmosphere of iodine vapour the brown locating spots will return.
It is important to distinguish between absorption and adsorption. Use Google to find out the difference.
Risk assessment
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updated: 11 April 2008
