Practical investigations
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I am doing the chemistry investigation on wine analysis. For the paper chromatography we do not have the available chemicals to develop the spots on the paper by spray. I am using ethanol as the solvent. If, after running and drying, I expose the paper to UV light will the deposited acids show a shadow (dark patch) on the paper? If not, is there any other way of seeing the spots?
Igloo suggests
The method described in the 'Investigating wines' tutorial on React involves the use of bromocresol green or bromophenol blue, which we think gives the best results.
However, if neither of these is available you will need to choose another indicator for which the colour change occurs in the region pH 3.5 – 5.0. You could try methyl orange which I am sure you will be able to find in your school or college laboratory, or, better still, “screened” methyl orange. If you are using methyl orange, the acids should show up as red blobs on a yellow background, whereas in the case of screened methyl orange the acids will appear purple on a pale green background.
Use of the Nuffield Book of Data (Table 6.6) will identify other possible indicators.
The spraying technique needs a good deal of practice and patience, and I would advise you to have several chromatograms on the go simultaneously, so you have plenty of opportunities to get it right.
The UV technique to which you refer is ideal in showing up certain components on paper, but I wasn’t aware that organic acids show up directly in UV light. Note that special TLC platges exist which are impregnated a fluorescor. Spots can show up black against a coloured background under UV light.
Carry out a risk assessment before carrying out any practical work. Consult your teacher about your plans and never work unsupervised. Take careful note of precautions needed when working withy UV light.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 17 February 2005
