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As the title says it, I am curious about why the sample (ie, an extract of plant's chlorphyl transferred onto paper) must not be dipped into the mobile phase (ie, the solvent which goes up the paper)?

My first guesses are that it is because the sample would dissolve into the solvent and only a small portion of the sample would go up the paper, but I am really keen to know if there is more to it than just this.

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Dipping sample to a mobile phase would cancel all the purpose of chromatography as a separation technique.

Imagine properly performed chromatography as the athletic race, where all runners start at the same point and time. The finish order is by their average speed.

Now imagine a crazy version of a New York marathone, where runners start in long sequence of runner batches. But nobody would think about registration of runner starts, so there would be no idea which runner was the fastest to be decorated as the winner.

Back to chromatography, instead of chromatographic spots ( PC, TLC) or peaks (HPLC, GC), there would be useless, smeared, overlapping long bands.

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  • $\begingroup$ There is only one mode of chromatography in which the sample is dissolved in the mobile phase and it is continuously passed through the column. It is called frontal chromatography. $\endgroup$ – M. Farooq Sep 14 '19 at 20:58

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