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Separation Techniques > SPE > Flashcards

SPE Flashcards

1
Q

What is SPE?

A

solid phase extraction (liquid-solid extraction)

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

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2
Q

SPE is basically the opposite of _____ extraction

A

solid-liquid

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3
Q

The selection of an appropriate SPE sorbent depends on ______

A

mechanisms of interaction between sorbent and analyte

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4
Q

major applications of SPE: (2)

A

sample cleanup

preconcentration of analyte (enrichment)

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5
Q

What is ‘sample cleanup?”

A

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

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6
Q

Why is ‘enrichment’ necessary, and how does SPE help achieve that

A

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

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7
Q

What advantages does SPE have over LLE?

A

less solvent

won’t form emulsions

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8
Q

Various SPE designs:

A 
cartridges
disks
96 wells
pipette tips
SPME
online SPE
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9
Q

current trends in SPE technology (new)

A

dispersive SPE

molecular imprinted polymers

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10
Q

What is a SPE cartridge?

A

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

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11
Q

4 steps to using SPE cartridge:

A
  1. condition
  2. load sample
  3. wash
  4. elute
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12
Q

What is an SPE extraction disk?

A

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

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13
Q

what are possible intermolecular forces between the analyte and sorbent (from weakest to strongest)? (6)

A 
dispersion forces
dipole-induced dipole
ion induced dipole
dipole-dipole
H bonds
Ion-dipole
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14
Q

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

A

adsorption, exchange, partitioning

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15
Q

types of SPE (4)

A 
reversed phase
normal phase (bonded)
normal phase (adsorption)
ion exchangers (cation & anion exchange)
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16
Q

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

A

False; used for nonpolar analytes (nonpolar sorbents)

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17
Q

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

A

normal phase (adsorption)

florisil, alumina

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18
Q

C18, C8, C2 are used in what type of SPE? What dissolving solvents are they paired with?

A

reversed phase

pair with methanol/water, ACN/water (polar)

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19
Q

The types of sorbent, analyte, dissolving solvent, and elution solvent used for reverse phase SPE:

A

sorbent: nonpolar (ex: C18)
analyte: nonpolar
dissolving solvent: polar (ex: water/ACN)
elution: hexane/CCl4 for nonpolar (methanol for polar)

20
Q

The types of sorbent, analyte, dissolving solvent, and elution solvent used for normal phase (bonded) SPE:

A

sorbent: polar (cyano, amino, or diol groups)
analyte: slightly/mod/strongly polar
dissolving solvent: nonpolar (hexane/CCl4)
elution: methanol

21
Q

What is a common polar elution solvent? What are common nonpolar elution solvents

A

polar: methanol
nonpolar: hexane, CCl4

22
Q

The types of sorbent, analyte, dissolving solvent, and elution solvent used for normal phase (adsorption) SPE:

A

sorbent: polar (SiOH, SiO3, Al2O3 groups)
analyte: slightly/mod/strongly polar
dissolving solvent: nonpolar (hexane/CCl4)
elution: methanol (depends on analyte type)

23
Q

The types of sorbent used for ion exchange SPE:

A

Sorbent: polar CHARGED: amino, N+, COOH, propyl sulfonic acid, aromatic sulfonic acid

24
Q

The types of dissolving solvent used and analytes targeted for ion exchange SPE:

A

solvent: water or buffer
analyte: ionic acid (use anion exchange) or ionic base (cation exchange)

25
Q

The pH of the buffer used as dissolving solvent in ion exchange SPE should ______

A

adjust pH to be pKa+2 (ionic acid) or pKa-2 (ionic base) so that analyte has a charged form

26
Q

what can be used for elution in ion exchange SPE?

A
  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
27
Q

For a hydrophilic analyte, you could try what types of SPE?

A 
ion exchange (if charged)
reverse phase to trap interferences (if neutral)
28
Q

For a hydrophobic analyte, you could try what types of SPE?

A 
reverse phase (neutral)
reverse phase or ion exchage (charged)
29
Q

What is hydrophilic-lipophilic balance?

A

value calculated in SURFACTANTS (Molecule with both hydrophilic and lipophilic parts) - balance of size/strength of the hydrophilic vs lipophilic parts

30
Q

Ideally, the analyte should be (eluted first/retained)

A

retained

want to get rid of impurities/interferences first

31
Q

What is the purpose of conditioning in SPE?

A

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)

32
Q

Describe what happens when the sample is loaded for SPE

A

liquid sample passed through, analyte retained on stationary phase => rest of matrix discarded

33
Q

What is the possible driving force for the flow through SPE?

A

gravity, pressure, vacuum

34
Q

low analyte recovery may happen if: _____ (during sample loading)

A
  1. flow rate too fast - no time to bind/interact

2. capacity of SPE phase too small for sample size (overload)

35
Q

What is the purpose of the washing step in SPE?

A

remove weakly bound interferences on the SPE phase with a weak solvent

36
Q

In some SPE procedures, there may be a ___ step after washing

A

drying

37
Q

What is the purpose of the elution step in SPE?

A

recover analyte by using strong solvent

38
Q

What needs to be considered iin method optimization for SPE?

A

SPE phase type

solvent type/volume (for all steps)

39
Q

Online SPE can be automated with ____

A

HPLC

sample loaded, washed (waste discarded) -> goes to LC

40
Q

Benefits of SPE:

A 
selective (wide range of phases available)
fast
low solvent consumption
preconcentration of analyte
can be automated
41
Q

Limitations of SPE

A 
need optimization (prevent breakthrough/overload)
incomplete removal of interferences
42
Q

What is ‘breakthrough?’

A

analyte doesn’t interact suffieicntly with sorbent (solvent too strong, not washed, etc) -> washes through right away and is lost

43
Q

What does SPME stand for? Who introduced it?

A

solid phase microextraction

introduced by J. Pawliswzyn from Waterloo

44
Q

What is solid phase microextraction

A

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)

45
Q

how does SPME indicate concentration in sample medium?

A

quantity extracted by SPME will be propoertional to the concentration in the sample medium

46
Q

Where is the sorbent in SPME?

A

the polymer coating (adsorbent) on the silica fibre

47
Q

Advantage vs disadvantage of SPME

A

good:
fast, less chemicals/materials, nondestructive

bad:
less precise?

Separation Techniques (12 decks)

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