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Separation Techniques in Food Analysis > Unit 4 > Flashcards

Unit 4 Flashcards

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1
Q

define membrane

A
  • a structure through which transfer may occur under a variety of driving forces
  • usually lateral dimensions are much greater than thickness
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2
Q

what are examples of driving forces?

A

concentration gradient
applied pressure
electrical potential

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3
Q

what are uses of membranes in food analysis?

A
  • sample prep: filtration, fractionation, cleanup, sterilization
  • extraction: liquid membrane extraction
  • analyte identification and quantification: membrane for sensors
  • specific studies
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4
Q

define filtration

A

the process of segregation of phases

eg. separation of suspended solids from a liquid or gas, usually by forcing a carrier gas or liquid through a porous medium

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5
Q

what is filtration primarily based on? what are other factors?

A

primarily based on size

other factors: shape and charge

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6
Q

what are two different types of filtration flows?

which one filtrates faster?

A
  1. direct flow filtration (conventional)

2. tangential filtration (Cross-flow)

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7
Q

describe direct flow filtration

what happens as volume filtered increases?

A
  • flow is perpendicular to membrane
  • molecules larger than pores accumulate at membrane surface
  • as volume filtered increases, mass accumulated may clog the filter and block flow of liquid through membrane
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8
Q

describe tangential filtration

A
  • no accumulation at membrane surface (b/c larger molecules flow in through)
  • large volume of sample can be processed without clogging
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9
Q

describe the graphs of conventional and cross-flow filtration

A

conventional:

  • beginning has high flow rate and low amount of particles at surface of membrane
  • as particles accumulate, flow rate slows

cross-flow
- flow rate and particles at membrane surface are unchanged

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10
Q

what equipment are commonly used for conventional filtration?

A
  • Buchner funnel
  • filtration units
  • filter paper
  • syringe filters
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11
Q

what are characteristics of filter papers?

A
  • retention characteristics: pore diameters in um
  • collection efficiency: % retained for specific particle size
  • wet burst: pressure in psi
  • content of ash: for mineral analysis
  • content of trace elements: for metal analysis
  • stability: pH
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12
Q

what are 3 common types of material for filter papers?

A
  1. cellulose paper
  2. glass fiber
  3. silicon-treated cellulose, polytetrafluoroethylene (PTFE)
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13
Q

what are types of syringe filters?

A
  1. hydrophilic membranes: cellulose acetate, polyamid, etc…
  2. hydrophobic membranes: PTFE
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14
Q

what are common issues with conventional filtration?

A
  1. filtrating fine particles = needs more time
  2. membrane clogging
  3. pressure (vacuum) is too strong = damages filter
  4. contamination of sample with filter residues
  5. adsorption of the analyte
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15
Q

which ones have low or high protein binding?

a) cellulose acetate
b) polyvinylidene fluoride
c) poyethersulfone (PES)
d) cellulose nitrate

A

a, b, c have very low protein binding

d has high protein binding

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16
Q

define microfiltration

what size of molecules are rejected

A
  • driven by pressure
  • membrane-based
  • small particles are dissolved
  • macromolecules larger than 0.1 um are rejected
17
Q

define ultrafiltration

what is the pore size range

A

process where a solution with a solute much bigger than the solvent molecule is removed from the solvent by using hydraulic pressure (which forces only the solvent to flow through a suitable membrane)
- pore size range is 0.001-0.1 um

18
Q

define nanofiltration

what is the pore size range

A
  • pressure drive
  • membrane based
  • separation process where particles and dissolved macromolecules smaller than 2nm are rejected
19
Q

what are examples of applications for microfiltration

A

sterilization
removal of microparticulates
pretreatment for ultrafiltration
fractionation

20
Q

how is culture media sterilized in food microbiology?

A

filtration through a membrane with 0.2um pore size

21
Q

what are applications of ultrafiltration in food analysis?

A
  1. concentration of high molecular weights
  2. fractionation using sequential ultrafiltration
  3. removal of salts or low molecular wt interferences
  4. separate free from bound molecules
22
Q

describe dialysis

A
  • used to separate molecules in solution based on size using a semi-permeable membranen
  • small molecules cross
    the membrane via diffusion, but large molecules can’t
  • membrane is a bag in which the sample is placed
  • membrane bag is placed in water/buffer solution
23
Q

what does HF-LPME stand for?

A

hollow fiber liquid phase micro extraction

24
Q

what two phases are in HF-LPME?

describe each

A

donor phase: where all molecules are

acceptor phase: only selected molecules

25
Q

describe electromembranes

A
  • voltage is applied to system
  • allows transportation of ionizable compounds from aqueous sample solutions across a supported liquid membrane (SLM) and into the acceptor phase in the hollow fiber

Separation Techniques in Food Analysis (13 decks)

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