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Kiha_3659
#1 Posted : Wednesday, July 31, 2019 5:12:37 AM
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TO whom it may concern,

I had a question regarding the LQ Chromatography Lab Techniques.

In a polar stationary silica phase, and a non-polar mobile phase,
a compound that is more polar has a lower Rf value and moves less than a nonpolar compound.

However, if we change the eluent to be more polar (ie aqueous alcohol), how will the Rf values change?

I heard that the compounds will significantly move faster up, regardless of its polarity.
Would the Rf values change (increase) than a less-polar mobile phase?
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INSTR_Katerina_102
#2 Posted : Wednesday, July 31, 2019 5:58:31 PM
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Hi Kiha,

The Rf of a compound is determined by the relative "amount of time" it spends in the mobile phase vs the stationary phase.

When you make the mobile more polar, all compounds tend to have a higher Rf and travel further. This is because the compounds start spending more time in the mobile phase, as the mobile phase starts being less significantly different from the stationary phase in terms of polarity.

Likewise, Rf values are smaller as compounds travel shorter distances with a non polar eluent.

Please let me know if this is unclear.

Cheers,

Katt
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