SPE Flashcards by Nancy He

What is SPE?

solid phase extraction (liquid-solid extraction)

analytes in a liquid are extracted with a SORBENT (solid material)

How well did you know this?

Not at all

Perfectly

SPE is basically the opposite of _____ extraction

solid-liquid

How well did you know this?

Not at all

Perfectly

The selection of an appropriate SPE sorbent depends on ______

mechanisms of interaction between sorbent and analyte

How well did you know this?

Not at all

Perfectly

major applications of SPE: (2)

sample cleanup

preconcentration of analyte (enrichment)

How well did you know this?

Not at all

Perfectly

What is ‘sample cleanup?”

isolate analyte from matrix and remove interfering molecules (remove impurities to make it into a cleaner form)

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

What advantages does SPE have over LLE?

less solvent

won’t form emulsions

How well did you know this?

Not at all

Perfectly

Various SPE designs:

cartridges
disks
96 wells
pipette tips
SPME
online SPE

How well did you know this?

Not at all

Perfectly

current trends in SPE technology (new)

dispersive SPE

molecular imprinted polymers

How well did you know this?

Not at all

Perfectly

What is a SPE cartridge?

plastic tube (like syringe) packed with sorbent; add sample and filter through

How well did you know this?

Not at all

Perfectly

4 steps to using SPE cartridge:

condition
load sample
wash
elute

How well did you know this?

Not at all

Perfectly

What is an SPE extraction disk?

similar to filter paper appearance; also use similarly (vacuum flask apparatus)

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

There are a large range of possible SPE mechanisms, such as:

adsorption, exchange, partitioning

How well did you know this?

Not at all

Perfectly

types of SPE (4)

reversed phase
normal phase (bonded)
normal phase (adsorption)
ion exchangers (cation &amp; anion exchange)

How well did you know this?

Not at all

Perfectly

T/F: reverse phase SPE is used for polar analytes

False; used for nonpolar analytes (nonpolar sorbents)

How well did you know this?

Not at all

Perfectly

Diatomaceous Earth and silica gel are examples of sorbents used in _______ SPE. What other sorbents are possible?

normal phase (adsorption)

florisil, alumina

How well did you know this?

Not at all

Perfectly

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)

How well did you know this?

Not at all

Perfectly

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?

1. buffer (adjust pH to be pKa +/- 2) 2. adjust pH back to pKa to make analyte or sorbent neutral 3. 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)

1. 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?