CIE A Level Chemistry (9701) exams from 2022

Revision Notes

7.6.11 Electrophoresis


  • Electrophoresis is an analytical technique which separates ions by placing them in an electrical field
    • This method is often used in biochemical analysis to identify and purify proteins
  • A sample of amino acids is placed between two oppositely charged electrodes
    • The positively charged ions will move towards the negative electrode
    • The negatively charged ions will move towards the positive electrode
  • The rate (how fast) at which the ions move towards the electrodes depends on:
    • The size of the ions: larger ions move more slowly
    • The charge of the ions: highly charged ions move more quickly
  • An electropherogram is the series of bands which are observed on the paper or gel after electrophoresis has occurred
    • Each band in the electropherogram corresponds to a particular species

Separating mixtures of amino acids by varying the pH

  • The charge on the amino acid ions depends on the pH of the solution
  • The movement of the ions to the electrodes during electrophoresis will therefore be affected by the pH
  • Consider a sample which consists of a mixture of three amino acids at pH 7
    • Amino acid A: lysine, side-chain is positively charged
    • Amino acid B: glycine, side chain is neutral
    • Amino acid C: glutamic acid, side chain is negatively charged

The sample consists of a mixture of three amino acids which are separated using electrophoresis

  • The amino acids in this mixture can be separated by electrophoresis
    • Amino acid C will move towards the positive electrode
    • Amino acid B will remain in the well where the sample is applied to the gel
    • Amino acid A will move towards the negative electrode
  • Since glutamic acid is larger than lysine, it will travel towards the positive electrode at a slower rate compared to lysine

Nitrogen Compounds - Electrophoresis Sample Results, downloadable AS & A Level Chemistry revision notes

Separation of a mixture of amino acids by electrophoresis

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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