Chapter 22 - Introduction To Analytical Separations Flashcards
When your solute is an acid or base, you must use the distribution coefficient in your calculation of q, rather than the partition coefficient.
True or false?
True
What is extraction?
Extraction is the transfer of an analyte, solute from one phase to another.
What is the best way to extract a solute that prefers to be in organic solvent from an aqueous solution?
Use multiple extractions with organic solvent.
What is the adjusted retention time of a solute?
The adjusted retention time of a solute is equal to the retention time minus the time required for mobile phase to travel through the column.
What is adsorption chromatography?
A solid stationary phase and liquid or gaseous mobile phase are used. Solute is adsorbed on the surface of the solid particles. The more strongly solute is adsorbed, the slower it travels through the column.
What is partition chromatography?
A liquid stationary phase is bonded to a solid surface, which is typically the inside of the silica chromatography column in gas chromatography. Solute equilibrates between the stationary liquid and the mobile phase, which is a flowing gas in gas chromatography.
What is ion-exchange chromatography?
Ions or cations are covalently attached to the stationary solid phase, usually a resin. Solute ions of the opposite charge are attracted to the stationary phase by electrostatic force.
What is molecular exclusion chromatography?
This technique separates molecules by size, with the larger solutes passing through more quickly. There is no attractive interaction between the stationary phase and the solute. The liquid or gaseous mobile phase passes through a porous gel. The pores are small enough to exclude large solute molecules but not small ones. Large molecules stream past without entering the pores. Small molecules take longer to pass through the column because they enter the gel and therefore must flow through a larger volume before leaving the column.
What is affinity chromatography?
It employs specific interactions between one kind of solute molecule and a second molecule that is attached to the stationary phase. After all of the other solutes have been washed from the column, the desired protein is eluted by changing the pH or ionic strength.
What is the relative retention?
The relative retention is:
- equal to the ratio of adjusted retention times of the solutes.
- equal to the ratio of capacity factors of solutes.
- equal to the ratio of partition coefficients of the solutes.
- is always greater than 1
What is analytical scale chromatography?
Thin columns, small volumes, and good separation. It is used for accurate separation of sample components for analysis.
What is preparative scale chromatography?
Uses fatter columns, larger volumes, and more sample for a poorer separation. It is used to separate bulk analyses, mainly for manufacturing purposes.
How do you scale up?
Keep the column length and linear flow rate constant, just increase the cross sectional area.
What must you do to obtain the most desirable peaks?
Separate the peaks so that they are further apart and narrow the peaks as well.
What does diffusion cause?
The diffusion of solutes in a solvent causes band spreading (wider peaks, longer elution times).
