SPE Flashcards
What is SPE?
solid phase extraction (liquid-solid extraction)
analytes in a liquid are extracted with a SORBENT (solid material)
SPE is basically the opposite of _____ extraction
solid-liquid
The selection of an appropriate SPE sorbent depends on ______
mechanisms of interaction between sorbent and analyte
major applications of SPE: (2)
sample cleanup
preconcentration of analyte (enrichment)
What is ‘sample cleanup?”
isolate analyte from matrix and remove interfering molecules (remove impurities to make it into a cleaner form)
Why is ‘enrichment’ necessary, and how does SPE help achieve that
concentration of analyte is too low in initial sample (need higher conc to be quantified)
SPE phase will concentrate large amounts -> elute and concentrate into small solvent volume
What advantages does SPE have over LLE?
less solvent
won’t form emulsions
Various SPE designs:
cartridges disks 96 wells pipette tips SPME online SPE
current trends in SPE technology (new)
dispersive SPE
molecular imprinted polymers
What is a SPE cartridge?
plastic tube (like syringe) packed with sorbent; add sample and filter through
4 steps to using SPE cartridge:
- condition
- load sample
- wash
- elute
What is an SPE extraction disk?
similar to filter paper appearance; also use similarly (vacuum flask apparatus)
what are possible intermolecular forces between the analyte and sorbent (from weakest to strongest)? (6)
dispersion forces dipole-induced dipole ion induced dipole dipole-dipole H bonds Ion-dipole
There are a large range of possible SPE mechanisms, such as:
adsorption, exchange, partitioning
types of SPE (4)
reversed phase normal phase (bonded) normal phase (adsorption) ion exchangers (cation & anion exchange)
T/F: reverse phase SPE is used for polar analytes
False; used for nonpolar analytes (nonpolar sorbents)
Diatomaceous Earth and silica gel are examples of sorbents used in _______ SPE. What other sorbents are possible?
normal phase (adsorption)
florisil, alumina
C18, C8, C2 are used in what type of SPE? What dissolving solvents are they paired with?
reversed phase
pair with methanol/water, ACN/water (polar)
The types of sorbent, analyte, dissolving solvent, and elution solvent used for reverse phase SPE:
sorbent: nonpolar (ex: C18)
analyte: nonpolar
dissolving solvent: polar (ex: water/ACN)
elution: hexane/CCl4 for nonpolar (methanol for polar)
The types of sorbent, analyte, dissolving solvent, and elution solvent used for normal phase (bonded) SPE:
sorbent: polar (cyano, amino, or diol groups)
analyte: slightly/mod/strongly polar
dissolving solvent: nonpolar (hexane/CCl4)
elution: methanol
What is a common polar elution solvent? What are common nonpolar elution solvents
polar: methanol
nonpolar: hexane, CCl4
The types of sorbent, analyte, dissolving solvent, and elution solvent used for normal phase (adsorption) SPE:
sorbent: polar (SiOH, SiO3, Al2O3 groups)
analyte: slightly/mod/strongly polar
dissolving solvent: nonpolar (hexane/CCl4)
elution: methanol (depends on analyte type)
The types of sorbent used for ion exchange SPE:
Sorbent: polar CHARGED: amino, N+, COOH, propyl sulfonic acid, aromatic sulfonic acid
The types of dissolving solvent used and analytes targeted for ion exchange SPE:
solvent: water or buffer
analyte: ionic acid (use anion exchange) or ionic base (cation exchange)
The pH of the buffer used as dissolving solvent in ion exchange SPE should ______
adjust pH to be pKa+2 (ionic acid) or pKa-2 (ionic base) so that analyte has a charged form
what can be used for elution in ion exchange SPE?
- buffer (adjust pH to be pKa +/- 2)
- adjust pH back to pKa to make analyte or sorbent neutral
- solvent with high ionic strength
For a hydrophilic analyte, you could try what types of SPE?
ion exchange (if charged) reverse phase to trap interferences (if neutral)
For a hydrophobic analyte, you could try what types of SPE?
reverse phase (neutral) reverse phase or ion exchage (charged)
What is hydrophilic-lipophilic balance?
value calculated in SURFACTANTS (Molecule with both hydrophilic and lipophilic parts) - balance of size/strength of the hydrophilic vs lipophilic parts
Ideally, the analyte should be (eluted first/retained)
retained
want to get rid of impurities/interferences first
What is the purpose of conditioning in SPE?
activate/wet pores of stationary phase, improve contact between sample and SPE
(ex: aqueous sample doesn’t like to contact hydrophobic C18, so need to first wet with MeOH)
Describe what happens when the sample is loaded for SPE
liquid sample passed through, analyte retained on stationary phase => rest of matrix discarded
What is the possible driving force for the flow through SPE?
gravity, pressure, vacuum
low analyte recovery may happen if: _____ (during sample loading)
- flow rate too fast - no time to bind/interact
2. capacity of SPE phase too small for sample size (overload)
What is the purpose of the washing step in SPE?
remove weakly bound interferences on the SPE phase with a weak solvent
In some SPE procedures, there may be a ___ step after washing
drying
What is the purpose of the elution step in SPE?
recover analyte by using strong solvent
What needs to be considered iin method optimization for SPE?
SPE phase type
solvent type/volume (for all steps)
Online SPE can be automated with ____
HPLC
sample loaded, washed (waste discarded) -> goes to LC
Benefits of SPE:
selective (wide range of phases available) fast low solvent consumption preconcentration of analyte can be automated
Limitations of SPE
need optimization (prevent breakthrough/overload) incomplete removal of interferences
What is ‘breakthrough?’
analyte doesn’t interact suffieicntly with sorbent (solvent too strong, not washed, etc) -> washes through right away and is lost
What does SPME stand for? Who introduced it?
solid phase microextraction
introduced by J. Pawliswzyn from Waterloo
What is solid phase microextraction
polymer coated fused silica fibre used to extract analytes:
- immersion (directly in liquid)
- headapace (from solid or liquid)
=> desorb analyte from fibre (put into injection port of GC or HPLC)
how does SPME indicate concentration in sample medium?
quantity extracted by SPME will be propoertional to the concentration in the sample medium
Where is the sorbent in SPME?
the polymer coating (adsorbent) on the silica fibre
Advantage vs disadvantage of SPME
good:
fast, less chemicals/materials, nondestructive
bad:
less precise?
