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Interpreting Chromatograms (AQA A Level Chemistry)

Revision Note

Stewart Hird

Last updated

Interpreting Chromatograms

  • The less polar components travel further up the TLC plate

    • Their Rf values are higher than those closer to the baseline

    • They are more soluble in the mobile phase and get carried forwards with the solvent

  • More polar components do not travel far up the plate

    • They are more attracted to the polar stationary phase

  • The extent of separating molecules in the investigated sample depends on the solubility in the mobile and stationary phases

  • Knowing the Rf values, of compounds being analysed, helps to compare the polarity of various molecules

Worked Example

A mixture of amino acids is analysed by thin layer chromatography (TLC). The TLC plate produced is shown below. Identify the amino acids in the sample using the table of values for Rf.

TLC Worked example a chromatogram, downloadable AS & A Level Chemistry revision notes

Answers:

Blue spot Rf value = 2.82 ÷ 4.63=  0.61 = Leucine

Green spot Rf value = 2.45 ÷ 4.63= 0.536 = Isoleucine

Red spot Rf value = 2.04  ÷ 4.63= 0.44 = Valine

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    Stewart Hird

    Author: Stewart Hird

    Expertise: Chemistry Lead

    Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.