Transcript Lecture 6

Lecture 6
Sample Preparation
Solid Phase Extraction
(Exhaustive Extraction)
Analyte either adsorps or absorbs to a
solid support
Advantages
•Large concentrations possible
•Limited use of solvents
•Very effective clean-up technique
Disadvantages
•Time consuming
•Precision can be difficult
•Expensive
Solid Phase Extraction - Air
(Exhaustive Extraction)
Environment
Vacuum
pump
Sorbent
N2 in
Lab
Sample
Sorbent
Ambient
air
Solid Phase Extraction - Air
(Exhaustive Extraction)
Sorbents
XAD
•High surface area (290-750 m2/g)
PUF
•Polyurethane foam
TENAX
•Moderate surface area (19-30 m2/g)
•Thermally stable, appropriate for thermal
desorption
Solid Phase Extraction - Water
(Exhaustive Extraction)
Environment
Sorbent
Pump
Water sample
Sorbent
Lab
Vacuum
manifold
Water
Solid Phase Extraction - Water
(Exhaustive Extraction)
Sorbents
Silica-based stationary phase
•Similar to LC phase - C18 most common
•Limited pH stability
•‘Finicky’ to handle
Polymeric
•Stable from pH 1-14
•Not ‘finicky’
Silica-based SPE cartridges
Procedure:
1. Condition cartridge
2. Load sample
3. Wash co-extractables
4. Elute analytes of interest
C18 tails
Si
Tails ‘solvate’ during step 1
(conditioning), will collapse if
the cartridge goes dry.
Extraction is ruined
Polymeric SPE cartridges
Procedure:
1. Condition cartridge
2. Load sample
3. Wash co-extractables
4. Elute analytes of interest
F F FF FF F
F
F
F F F F F FF F
O
P O
O
No tails to ‘solvate’, and so
extraction can continue even if
cartridge goes dry
Polymeric SPE cartridges
+
NH
N
+
NH2
F F FF FF F
F
F
F F F F F FF F
O
P O
O
NH
F F FF FF F
F
F
F F F F F FF F
O
P O
O
Because of the wide pH stability are able to use pH to control
extraction. Very selective and effective extraction technique.
Solid Phase Micro Extraction (SPME)
Only equilibrium extraction method described here.
Often used to observed volatile materials in a
laboratory setting.
N2 in
Sample
Sorbent
Solid Phase Micro Extraction (SPME)
N2 in
Sample
Sorbent
Solid Phase Micro Extraction (SPME)
SPME holder
SPME fibre
Sample
Solid Phase Micro Extraction (SPME)
SPME fiber
k
k
Sample