AQA A Level Chemistry

Revision Notes

7.11.5 Interpreting Chromatograms

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

Analysis of a compound by GLC shows the presence of four components, A, B, C and D.

i) Which compound is present in the greatest quantity?

ii) Which compounds were present in equal amounts?

iii) Which compound had the strongest interaction with the stationary phase?

Answers:

i) D (the larger the relative size of the peak, the greater the quantity of that substance present)

ii) B and C (the peak sizes are equal)

iii) D (the larger the retention time, the greater the interaction of that component with the stationary phase)

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