Why mixtures split into bands

Science · Chemistry · ages 19-20

Name ______________________ Date ____________

Why do components spread into separate bands?
- The column shakes them apart
- Each splits its time between the phases differently, so speeds differ
- They react with each other
What are the two phases in any chromatography setup?
- Two moving liquids
- A still stationary phase and a flowing mobile phase
- A solid and a vacuum
The dead time is marked by a component that washes through without being retained.
Circle one: True False
Dead time is 2 minutes and a peak arrives at 10 minutes. Type its retention factor k.
Answer: ______________
Dead time is 1 minute and a peak arrives at 4 minutes. Type its retention factor k.
Answer: ______________
Two peaks have k values of 1 and 4. Which interacted more with the stationary phase?
- The peak with k of 4
- The peak with k of 1
- Both interacted equally
In the plate model, more plates give sharper peaks because each plate is one equilibration stage.
Circle one: True False
You swap a polar stationary phase for a nonpolar one. What happens to a polar analyte?
- Its retention grows longer
- Nothing changes at all
- Its retention shortens, since the grip is gone

Answer key

For grown-ups. Fold this page away before handing over the rest.

Each splits its time between the phases differently, so speeds differ · Different sticking balances give different travel speeds.
A still stationary phase and a flowing mobile phase · One phase stays put while the other carries the sample past it.
True · Unretained travellers clock the pure travel time of the mobile phase.
4 · Extra wait 8 divided by dead time 2 gives 4.
3 · Extra wait 3 divided by dead time 1 gives 3.
The peak with k of 4 · Bigger k means a longer stuck spell on the stationary phase.
True · Repeated equilibration tightens bands instead of smearing them.
Its retention shortens, since the grip is gone · Like holds like, so the polar analyte loses its anchor.