Chromatography
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Define chromatography ?
Family of techniques on separating mixtures based on different interactions with its absorbment material
What are the common elements that all chromatographic methods have in common ?
A stationary phase A Mobile phase A method for detecting the sample A way of adding the sample to be separated A mechanism to make the sample components move relative to the stationary phase
In what ways can the sample be separated ?
Chemical properties such as hydrophilic, hydrophobic and polarity Physical properties such as their size
What is analytical chromatography?
Measure or identify of compounds
What is preparative chromatography?
To purify or isolate compounds
What is the stationary phase ?
The part that doesn’t move
What is the mobile phase ?
The part that flows
What is partitioning?
How a substance divides its time between both Stationary and mobile phases. For example a substance moves faster if it prefers the mobile phase and slower if it prefers the stationary phase
What is the mobile phase made of ?
Gas or liquids
What is the stationary phase also known as ?
Absorbent surface
What is the symbol for the equilibrium constant ?
Kc
What is equilibrium constant equation for chromatography
KC = [ stationary / mobile ]
What does equilibrium in chromatography mean?
This is when molecules constantly move back and forth in between the stationary and mobile phase
What does it mean if you have a high Kc value ?
This means you increase the stationary phase according to the equation so the compound spends more time/ is slower in the stationary phase
What does it mean if you have a low Kc value ?
This means you increase the mobile phase according to the equation so the compound which is a gas it liquid moves faster
What does Rf stand for ?
Retention factor
What is retention time ?
The Difference in time travel
Why does a higher surface area mean greater separation ?
A higher surface area mean more sites for the molecules to interact such as absorb or desorb increasing the effectiveness of the separation
Name the 5 different mechanisms of separating compounds
Adsorption Ion exchange Size exclusion Affinity Partition and bonded phase
What type of stationary and mobile phase does absorption use ?
Solid stationary phase Liquid or gas mobile phase
How are molecules separated in absorption ?
Molecules are separated by how strongly they absorb onto the solid surface depending on the strength of the interaction and they can later desorb due to equilibrium Molecules that bind more strongly move slowly against the surface and vice versa.
What is partition phase ?
Separation occurs because solutes partition between 2 immiscle phases
What type of stationary and mobile phase does partition phase use ?
Stationary phase would be a liquid film coated on solid support Mobile phase would be a liquid or gas that moves past it
What type of stationary and mobile phase does bonded phase use ?
Instead of coating a liquid onto a solid , the stationary phase is chemically bonded to the solid surface so it’s more stable and durable Mobile phase is polar which is usually water and a solvent