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GCSE Combined Science · key term
The pencil line on chromatography paper where the samples are initially placed and from which their travel distances are measured.
Used by AQA and OCR
Specification 4.2.2.4 · Paper 1, Paper 2
Revise: Plant Pigments and ChromatographyDraw a pencil baseline near the bottom of the paper. Mark positions for the samples along it, leaving enough space between them to keep their spots separate.
Specification B6.1c, C2.1i · Biology Paper 2, Chemistry Paper 1
An initial measurement used for comparison with later measurements, such as a population estimate before a conservation scheme begins.
Measure both distances from the pencil baseline, measuring to the centre of each spot rather than its edge.
Give a reason for practical choices: pencil does not travel with the solvent, and keeping the baseline above the solvent prevents the samples washing into it.
Measure both distances from the baseline, not from the bottom of the paper.
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Conservationists need a baseline measurement, such as an estimate of a population before protection begins, followed by repeated measurements.
The starting line on a chromatogram where the samples are placed.
