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Separation Techniques > Membranes > Flashcards

Membranes Flashcards

1
Q

What is the definition of ‘membrane?’

A

structure with much greater surface area (lateral dimensions) than thickness, can transfer substances through with various driving forces

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2
Q

driving forces that can be used in membrane separations:

A

concentration gradient
applied pressure
electric potential

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3
Q

What are membranes used for in food analysis? (4)

A

sample prep (filter, fractionation, cleanup, sterilize…)
extraction
analyte identifiation/quantification
speciation studies

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4
Q

What is filtration?

A

segregation of phases (suspended solids in liquid or gas) by forcing it through a porous medium (filter)

separation based on size (also shape, charge)

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5
Q

a coffee filter has pore size of about _____

A

20 microns

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6
Q

The 2 flow types in filtration:

A

direct flow

tangential flow

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7
Q

What is direct flow filtration:

A

flow of feed is perpendicular to membrane; molecules that don’t fit through pores will accumulate on surface

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8
Q

What is tangential flow filtration?

A

feed is parallel to membrane, some will pass through (filtrate) while larger particles will keep flowing with rest of liquid (retentate)

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9
Q

Compare the performance of direct vs tangential flow filtration:

A

direct: faster at first, but then flow will slow and stop as the mass of retentate accumulates (clogs filter)
tangential: slower at first, but continues at same rate even with large volumes

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10
Q

Tangential flow is also called ______

Direct flow is also called _____

A

cross flow

conventional flow

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11
Q

Common designs of conventional filtration devices

A

buchner funnel + vacuum flask + filter paper

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12
Q

What AOAC approved food analysis method requires use of filtration?

A

measurement of soluble and insoluble dietary fibre; filter sample after enzymatic digestion

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13
Q

What are important characteristics of filter paper to consider? (6)

A

retention characteristics (pore diameter)
collection efficienty (% retained for specific size)
wet burst (pressure it can tolerate)
content of ash
content of trace elements
stability (vs pH, etc)

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14
Q

1 bar = ____ psi

A

14.5

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15
Q

2 common filter types used in the lab:

A

filter paper

syringe filter

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16
Q

What are 3 types of filter paper

A

cellulose paper (ashless; rinsed with acid and UP water)
glass fibre
silicon-treated cellulose, Polytetrafluorethylene

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17
Q

2 types of syringe filters:

A

hydrophilic: cellulose acetate, PA, PP, PES, Nylon, PVDF

hydrophobic membrane: PTFE

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18
Q

common issues with conventional filtration (5)

A

filter time (finer particles -> more time)
membrane clogging
pressure (vacuum) too strong -> damages filter
filter residue contaminates sample
adsorption of analyte

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19
Q

What are some filter materials with very low protein binding? (3)

A

cellulose acetate
PVF (polyvinylidene fluoride)
PES (polyethersulfone)

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20
Q

What is the protein binding ability of cellulose nitrate filter?

A

high protein binding

21
Q

Put in decreasing pore size order:
microfiltration
nanofiltration
ultrafiltration

A

microfiltration (0.1 um)
ultrafiltration (0.001-0.1um)
nanofiltration (2nm)

22
Q

microfiltation, nanofiltration, and ultrafiltration are usually ____ driven

A

pressure

23
Q

applications of microfiltration: (4)

A

sterilization
removal of microparticulates
pretreatment for ultrafiltration
fractionation (separate different components one step at a time)

24
Q

How does microfiltration achieve sterilization?

A

membranes with 0.2microns (or less) pore size will remove bacteria, mold, and yeast

25
Q

T/F: ultrafiltration will achieve sterilization

A

True, even microfiltration can achieve sterilization (<0.2 microns)

26
Q

Examples of ultrafiltration designs (2)

A

disposable UF

centrifugal UF

27
Q

Applications of ultrafiltration: (3)

A

protein concentration
peptide fractionation
separate free vs bound molecules

28
Q

How is ultrafiltration used for protein concentration?

A

protein solution added to tube with filter -> centrifuge (proteins retained due to large size) -> discard buffer that passed through, and resuspend retentate -> repeat as needed

29
Q

How is peptide fractionation done?

A

use various ultrafiltration pore sizes: first filter out largest ones, then use smaller pore size to filter out smaller ones, and then an even smaller one, etc

30
Q

How can ultrafiltration be used to separate food dyes bound to serum albumin?

A

human serum albumin is large protein. dye-protein complex is large and cannot pass through; unbound dye molecules can pass through filter (measure absorbance of filtrate)

31
Q

What is the method used to separate molecules in solution based on size using a semi-permeable membrane? What is the driving force?

A

dialysis

concentration gradient

32
Q

Describe the process of dialysis

A

sample placed in bag-shaped membrane, sealed and placed in water/buffer with gentle agitation

small molecules slowly diffuse out until reach equilibrium

33
Q

examples of applications of dialysis:

A

carbohydrate purification (separate large vs small polysaccharides)

in-line dialysis for determine nitrate/nitrite in milk

34
Q

T/F: dialysis is a fast method

A

False; relatively slow

35
Q

What are hollow fibre membranes?

A

hollow fibre made of artificial polymers, porous structure

36
Q

What is the flow type in hollow fibre membrane filtration?

A

cross-flow (tangential)

37
Q

What is a supported liquid membrane?

A

formed by dipping (filling) a hollow fibre with organic solvent -> immobilized in the walls (capillary action)

then fill the fibre lumen with solvent (organic or aqueous) to form the acceptor phase

38
Q

The 2 types of hollow fibre LPME:

A

2 phase

3 phase

39
Q

describe 2 phase LPME:

A

hollow fibre is dipped with organic solvent to form supported liquid membrane

inside of fibre filled with organic solvent (acceptor phase)

dipped into sample, swish around, analyte extracted into acceptor phase

40
Q

Describe 3 phase LPME:

A

hollow fibre is dipped with organic solvent to form supported liquid membrane

inside of fibre filled with aqueous solvent (acceptor phase)

dipped into sample, swish around, analyte extracted into acceptor phase

41
Q

T/F: a 3 phase LPME uses an organic solvent as the acceptor phase

A

False; uses aqueous solution

42
Q

What prevents the analyte from exiting the acceptor phase in 3-phase LPME?

A

once enter acceptor phase -> become ionized (cannot diffuse past organic SLM anymore)

43
Q

How should you choose an acceptor phase for 3 phase LPME?

A

basic analyte -> use acidic solvent

acidic analyte -> use basic solvent

44
Q

LPME methods are usually coupled to _____

A

GCMS or HPLC or LCMS

45
Q

What is electromembrane extraction? What analytes is it used for

A

mini form of liquid-liquid extraction; similar set up as LPME
apply VOLTAGE -> electrical potential acts as driving force

used for charged compounds (can adjust voltage and charge)

46
Q

For EME, the solution must be adjusted so the analyte remains in a ____ state

A

charged

47
Q

For a basic (+) analyte, the anode is located in the ____, while the cathode is located in the ____

A

solution

acceptor phase

48
Q

A cathode is (positive/negative) while an anode is (positive/negative)

A

negative

positive

Separation Techniques (12 decks)

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