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GCSE Chemistry · key term
The pencil line on which samples are placed at the start of paper chromatography.
Used by AQA and OCR
Specification 4.8.1.3 · Paper 2
Revise: Chromatography TechniquesDraw a straight origin line in pencil near the bottom of a strip of chromatography paper. Mark the sample positions on this line, then use a separate capillary tube for each sample to add a small, concentrated spot. Separate tubes prevent one sample contaminating another.
Specification C2.1g · Paper 1 (Foundation), Paper 3 (Higher)
The pencil line on which samples are placed before the chromatogram is developed.
Revise: Chromatography TechniquesDraw a straight origin line in pencil near the bottom. Pencil is used because graphite does not dissolve and travel with the solvent; ink from a pen could separate and interfere with the results.
Measure both distances from the origin line: to the centre of the substance spot and to the solvent front.
Use pencil for the origin line because graphite does not dissolve in the solvent; ink could separate and produce extra spots.
Keep the origin line above the solvent level or the samples may dissolve directly into the solvent reservoir.
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