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- Posts: 15
- Joined: Tue Dec 30, 2014 2:06 am
The capacity factor for nicotine separated on a C8 non-polar stationary phase is shown
below.
Capacity Factors for Nicotine at three Different pH values
pH3 pH5 pH7
0.00 0.13 3.11
Why does the capacity factor increase as the pH increases?
The pka of nicotine is 3.15, so at a pH above 3.15, nicotine will become deprotonated and therefore have a negative charge which makes it more attracted to the polar mobile phase which means it moves faster through the column and therefore the retention time will decrease and so capacity factor should decrease.
What is wrong with my thinking?