LECTURE 9 - Solvent extraction and Chromatography basics

What is the basis of solvent extraction

It is the transfer of an analyte solute from one phase to another

What is always going to be phase one

the aqueous (water phase)

What is always going to be phase 2

The organic phase

what does miscible mean

the form one single phase

What does immiscible mean

solvents form distinct phases

what is the distribution constant

It is teh equilibrium constant between both phases

what is more efficient one large extraction or multiple smaller extractions

multiple smaller extractions

elaborate on the pH effects on solvent extraction

pH is plays a crucial role in extraction as the equation depends on wether they are an acid or a base as they can be found in two forms, a charged fprm or a non-charged form

How would you extract a base in the aqueous layer

You would lower the pH to convert the base to BH+ and it will be charge and able to interact with water

How would you extract a base in an aqueous phase

You would raise the pH to converts the BH+ to B and its non charged form will be able to interact with nonpolar organic phase

How would you extract an acid in water

You would raise the pH to convert HA into A- (charged and can interact with water)

How would you extract an acid in an organic solvent

You would lower the pH to convert A- to HA now uncharged and can interact with the polar environment

What is the distribution equation for a base

D = KD*Ka/ Ka+[H+]

What is the distribution equation for an acid

D = Kd*[H+]/[H+]+Ka

What is the role of a metal chelator

It is a ligand used to extract metal complexes that are not soluble in organic solvents. Essentially how they work is the ligand donates protons after binding to a metal complex resulting in a neutral formed complex that will displace into the organic phase. So you adjust the pH accordingly to extract the metal. Low pH = ligand remains protonated and higher pH = it will bind to metal cause it will be deprotonated.

I want my metal to bind in solvent extraction what do I do

You need to increase your pH so that the metal chelator ligand will be deprotonated and will therefore be able to bind to a charged metal creating a neutral compound that will be displaced to the organic layer

What is the basis of chromatography

It is a seperation technique in which a molecules in a mobile phase are seperated because of their different affinities for a stationary phase

Stationary phase

Solid or liquid that stays in place inside the column

Mobile phase

solvent that contains the analyte that moves through the column

Define elution

The process of passing liquid or gas through a chromatography column

What is the eluent

Fluid that enters the column

What is the eluate

The fluid exiting the column

What is adsorption chromatography

In this technique the stationary phase is a solid and the mobile phase is a liquid or gase and the solute interacts by sticking (Adsorbing) to the surface of solid particles

Elaborate on partition chromatography

In partition chromatography the stationary phase is a liquid bonded to a solid surface and the mobile phase is a gas. The solute will then equilibrate between the stationary liquid and mobile phase and this back and forth movement results in seperatio

Elaborate on the basics of ion exchange chromatography

In ion exchange chromatography the stationary phase is a resin with anions or cations that are covalently attached and the mobile phase is a liquid and solute ions of opposite charge will inetract with teh stationary phase back and forth mouvement again results in seperation

Elaborate on molecular exclusion chromatography

Molecules are strictly deperated by size there is no attractive form between the stationary phase rather the liquid or gaseous phases pases through a porous gel. Large molecules cant go through the pores and are quicker than small molecules that need to slowly go down

Elaborate on affinity chromatography

It is the most selective type of chromatography as the column exploits a specific interaction between two kidsn of solute molecules where one is attached to the stationary phase

What is the use of an analytical scale chromatography

These include thin columns where small volumes are tested. Used for accurate seperation of a sample for analysis

Elaborate on preparative scale chromatography

This employs a fatter column

When you scale up what should you do

You should increase the cross sectional area and keep the cross sectional area consistant

Define the volume flow rate

it is the volume of solvent per unit time that passes through the column

define linear flow rate

This is the distance the solvent travels per unit time

what is the seperation factor

ratio of adjusted retention times

Define the retention factor

It is the ratio of distance the solute travels to the distance of the mobile phase

• When you have a low rf = string interaction with the stationary phase

• When you have a high rf = weaker interaction with the stationary phase

what is the retention volume

The volume of the mobile phase required to elute a particular solute

What is the relationship between time and retention volume

They are proportional.