Question

You are performing a gradient elution and are instructed to begin with a low polarity solvent (petroleum ether) and continue to increase solvent polarity with MTBE. Why are the mobile phases added in order of increasing polarity rather than in the order of decreasing polarity?

Answer 1

Answer:

The eluting strength of a solvent is primarily related to how strongly it adsorbs onto the  adsorbent and because typical adsorbents are highly polar; thus, eluting strength increases  with solvent polarity.

Explanation:

The polarity of a solvent makes it more suitable for elution in a polar adsorbent. Hence the choice of solvents should be in order of increasing rather than decreasing polarity. polarity must increase and not decrease