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Separation Techniques in Food Analysis > Unit 3 > Flashcards

Unit 3 Flashcards

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1
Q

what is SPE?

what is the principal behind it?

A

solid phase extraction

process by which the analyte(s) suspended or dissolved in a liquid is selectively extracted with a sorbent material (liquid-solid extraction)

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2
Q

what does the selection of an appropriate sorbent in SPE depend on?

A

the mechanism(s) of interaction between the sorbent and analyte of interest

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3
Q

what are 2 main applications of SPE? describe them

A
  1. sample cleanup:
    - isolation of the analyte(s) from the matrix and possible interfering molecules
    - eg. weakly bound impurities washed out and desired analyte is eluted in a cleaner form
  2. preconcentration of the analyte:
    - when conc of the analyte is too low in the initial sample
    - large amounts of sample is concentrated on the SPE phase
    - extract is then eluted and concentrated to a small solvent volume
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4
Q

SPE is an alternative to what?

A

other extractions such as LLE which need large volumes of immiscible solvents

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5
Q

describe the analytical procedure for the determination of caffeine

A
  1. sample dilution
  2. SPE cartridge and conditioning
  3. sample load
  4. washing step
  5. caffeine elution
  6. filtration
  7. HPLC analysis
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6
Q

what are the 4 main steps of SPE?

what is the input and output of each?

A
  1. conditioning:
    - input water
    - output water
  2. loading sample
    - input sample (containing analyte
    - output: interferences
  3. washing:
    - input water
    - output: more interferences
  4. eluting:
    - input water
    - output: analyte
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7
Q

how many wells are in a SPE plate?

A

96

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8
Q

what does the large diversity of interactions of intermolecular forces between analyte and sorbet indicate?

A

there can be many possible SPE mechanisms (ie. adsorption, exchange, partitioning)

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9
Q

for non polar analytes, what are good…

a) dissolving solvents
b) elution solvents
c) sorbents

A

a) methanol/water, acetonitrile/water
b) hexane and chloroform
c) octadecyl, octyl, ethyl, phenyl

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10
Q

for slightly polar analytes, what are good…

a) dissolving solvents
b) elution solvents

A

a) hexane and chloroform

b) methanol

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11
Q

anionic exchange resins are ____ (Acidic/basic)

A

basic

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12
Q

cationic exchange resins are _____ (acidic/basic)

A

acidic

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13
Q

what is HLB?

A

hydrophilic-lipophilic balance

the measure of the degree to which a surfactant is hydrophilic or lipophilic

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14
Q

describe the purpose of the conditioning step of SPE

example?

A
  • activates and/or wets the pores of the stationary phase
  • improves contact between sample and SPE phase
  • example: C18 is a hydrophobic phase. The aqueous sample doesn’t come in contact with the C18 phase. MeOH is used to “wet” the phase
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15
Q

describe the purpose of the loading sample step in SPE

A
  • liquid sample is passed through the SPE phase
  • analyte is retained on stationary phase
  • unretained sample matrix is discarded
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16
Q

what is the driving force of the loading sample step in SPE

what does it elute?

A

driving force: gravity, pressure, vacuum

this elutes the unretained sample matrix, which is discarded

17
Q

when does low analyte recovery occur?

A

when the flow rate is too fast

or when the capacity of the SPE phase is too small for the sample size (overload)

18
Q

describe the purpose of the washing step in SPE

A
  • weakly bound interferences are washed off the cartridge

- uses a weak solvent

19
Q

when can the cartridge go through drying?

A

after washing for some analytes

20
Q

describe the purpose of the final elution step in SPE

A
  • strong solvent is eluted to recover the analyte(s) of interest from the SPE phase
  • fraction(s) containing the analytes are collected

eg. after extracting on C18 cartridges, the analytes are recovered using elution with methanol

21
Q

what are benefits of SPE?

limitations?

A

benefits

  • wide range of SPE phases available
  • relatively fast; no reflux, shaking, or phase separation steps
  • low solvent consumption
  • pre-concentration of analyte
  • can be automated

limitations

  • needs optimization to prevent breakthrough/overload
  • incomplete removal of interferences
22
Q

what is SPME?

A

solid phase microextraction

23
Q

what is used for extraction of analytes in SPME? how is it used?

A
  • a polymer coated fused silica fiber that selectively adsorbs analytes of interest
  • used directly in the liquid by immersion
  • used from a solid or liquid by headspace extraction
24
Q

in SPME, what happens after extraction?

A

analytes are desorbed from fiber by exposing fiber in the injection port of a GC or in the desorption chamber of a SPME interface

25
Q

in SPME, the quantity of analyte extracted by the sorbent is proportional to what?

A

to its concentration in the sample medium in the case of equilibrium

26
Q

in SPME, what happens to…

a) volatile analytes
b) non-volatile analytes

A

a) adsorbed onto the sorbent fiber (in air)

b) adsorbed onto sorbent fiber (in liquid)

Separation Techniques in Food Analysis (13 decks)

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