In chromatography, if a pen were used to draw the origin line instead of a pencil, what would likely happen?

• A. The pen ink could dissolve in the solvent and contaminate the chromatogram.
• B. The pen would not affect the results.
• C. The ink would color the background unhelpfully.
• D. The pen would dry too quickly.

Answer: (A)

In chromatography, the origin line should be drawn with pencil because graphite is largely insoluble in the solvents used. If a pen is used, the ink contains dyes that can dissolve in the solvent and travel up the paper with the mobile phase. As the solvent front advances, the ink can migrate too, contaminating the chromatogram with additional colored spots or lines. This makes it hard to see where the sample components separate and can distort the measured positions, giving inaccurate results. Pencil stays behind at the origin, so only the sample components move, giving a clear, interpretable chromatogram.