1. Extraction Dissolution Extraction Chromatography
Purification based on relative affinity for extracting media
May isolate analyte from solid, liquid or gaseous matrices
Can involve extraction to solvent or solid phase media
The following are readable reviews of this stage of sample preparation:
Roger M Smith. (2003) Before the injection – modern methods of sample preparation for separation techniques J. Chromatography A, 1000, 3-27.
Kathy Ridgway et. al.(2007) Sample Preparation techniques for the determination of trace residues and contaminants in food. J. Chromatography A, 1153,

2. Analytes in Solid Samples
Particle size is important – so may need pre-extraction homogenisation
Solvent is chosen to enhance selectivity
May also require
Recycling (Soxhlet)
Heating (boiling, or superheating under pressure)
Supercritical fluids
Microwave and sonic radiation (difficult to automate)
Aqueous pastes (eg meat or plant tissue) require special care – sometimes using powdered matrix
Insoluble analytes may be pyrolysed (to produce soluble fragments)
Volatile analytes may be “thermally desorped” and then treated as for gases

3. Analytes in Solution
Biphasic (aqueous/organic) liquid-liquid extraction but has problems
Costly in solvent
Waste/environmental concerns increae cost
Concentration of solvent gives loss of volatile analytes and concentration of solvent impurites
Purge and Trap (volatile analyte flushed out by gas)
Dialysis
Uses a membrane to separate layers / increase selectivity
Solid phase extraction/microextraction

4. Solid-Phase Extraction
Adsorbent coated on
packed powder
fibre/capillary
beads
stirrer bar
Advantages include
low waste
automatable
effective concentration
May be “in-line”
Performance is affected by
flow rate
preconditioning
Brand
matrix
Most chromatographic phases available
C18
ion exchange
size exclusion
chiral, immunoaffinity and molecular imprinted
Requires desorption post extraction
by solvent
thermally (GC injection port)

5. Gaseous Analytes Problems Sample preparation focuses on trapping
low concentration
difficult to store
Sample preparation focuses on trapping
cooling
bubbling through solution
adsorbing to fibre
Need to control for misting and desolvation