FOR10002 Lecture Notes - Lecture 6: Elution, Solution, Electrical Resistance And Conductance
FORENSIC SCIENCE - FOR10002
WEEK 6
MODERN ANALYTICAL
TECHNIQUES
Chemical Separation Techniques!
Complete or partial separation will depend on the goal of the analysis.
Usually it is not necessary (or possible) to separate all components.!
Separation results in a redistribution of components which always
requires an input of energy.!
Basic Components in Chromatography!
•Solutes: chemical species or analytes to be separated !
•Stationary Phase: a solute-free space where the solute can be selectively retained !
•Mobile Phase: continuously moving solute-free phase that can carry the solute to a fresh area
of stationary phase!
find more resources at oneclass.com
find more resources at oneclass.com
Classification of Methods!
Categorising Liquid Chromatography Methods!
Solute Polarity!
The distribution of electrons around the atoms in a molecule creates regions that appear charged
to other molecules !
•A polar molecule has regions of excess negative
and positive charge !
•A non-polar molecule has the same charge all
over!
General Classification
Specific Method
Stationary Phase
Type of Equilibrium
Liquid
Chromatography (LC)
Mobile Phase: Liquid
•Liquid-liquid; or
partition!
•Liquid-bonded phase!
•Liquid-solid; or
absorption!
•Ion exchange!
•Size exclusion
•Liquid absorbed on a
solid!
•Organic species
bonded to a solid
surface!
•Solid !
•Ion-exchange resin!
•Liquid in interstices of
a polymeric solid
•Partition between
immiscible liquids!
•Partition between
liquid and bonded
surface!
•Adsorption!
•Ion-exchange!
•Partition/sieving
Gas Chromatography
(GC)
Mobile Phase: Gas
•Gas-liquid!
•Gas-bonded phase!
•Gas-solid
•Liquid absorbed on a
solid!
•Organic species
bonded to a solid
surface!
•Solid
•Partition between gas
and liquid!
•Partition between
liquid and bonded
surface!
•Adsorption
Supercritical-fluid
Chromatography (SFC)
Mobile Phase:
Supercritical-fluid
•Organic species
bonded to a solid
surface
•Partition between
supercritical fluid and
bonded surface
find more resources at oneclass.com
find more resources at oneclass.com
Modes of Separation!
ADSORPTION
Adsorption is the interaction of a solute with the surface of the stationary
phase.!
PARTITION
When partition occurs, the solute moves between
the mobile phase and a liquid stationary phase coated on a supporting
material.!
ION EXCHANGE
During ion-exchange, the solute interacts with a stationary phase due
to ionic forces. (This is an anion exchange surface).!
SIZE-EXCLUSION
During size-exclusion, small solute particles are
detained within the channels of a porous stationary phase.!
Elution Chromatography!
!
Quantitative Measures!
•tr is the time between injection and
detection or retention time !
•tm is the time for an unretained component
to reach the detector or void time (also
known as the solvent front) !
•w is the peak width at the baseline!
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Complete or partial separation will depend on the goal of the analysis. Usually it is not necessary (or possible) to separate all components. Separation results in a redistribution of components which always requires an input of energy. Mobile phase: gas: gas-liquid, gas-bonded phase, gas-solid. The distribution of electrons around the atoms in a molecule creates regions that appear charged to other molecules: a polar molecule has regions of excess negative and positive charge, a non-polar molecule has the same charge all over. Adsorption is the interaction of a solute with the surface of the stationary phase. When partition occurs, the solute moves between the mobile phase and a liquid stationary phase coated on a supporting material. During ion-exchange, the solute interacts with a stationary phase due to ionic forces. (this is an anion exchange surface). During size-exclusion, small solute particles are detained within the channels of a porous stationary phase.
