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Medicine analysis and design > chromatography > Flashcards

chromatography Flashcards

1
Q

explain what chromatography is

A

method of separating components in a mixture that are distributed between a mobile phase and stationary phase, based on their interaction with the stationary phase.

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2
Q

give some examples of POLAR stationary phases

A
  1. silica
  2. alumina
  3. paper
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3
Q

example of a non-polar stationary phase

A

charcoal

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4
Q

explain partition chromatography

A
  • both phases are liquid
  • ## a liquid stationary phase is bonded onto silica support
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5
Q

why is chromatography needed in pharmacy

A
  • drug design and manufactures
  • quality assurance
    -clinical trials
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6
Q

list some quality issues with chromatography in pharmaceuticals

A
  1. quality of actives (purity, identity, content)
  2. quality of excipients (raw materials)
  3. cleanliness of manufacturing plant.
  4. stability testing. including prediction of degradation pathways.
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7
Q

draw out a diagram of a gas chromatography instrument

A

COMPONENTS:

  • gas cylinder on the left with regulator on top
  • autosampler/injector
  • inlet
  • two columns with a modulator inbetween
  • the gc oven
  • detector feeding info to a computer
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8
Q

briefly explain the process of gas chromatography.

A
  • a sample mixture heated 50degree C higher than its BP
  • top of column is lower than heating block to encourage concentration condensation
  • mixture carried through column by a continuous flow of inert gas.
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9
Q

what are GC columns packed with?

A

solid particles or a solid support coated with a liquid either by adsorption or chemically bonded to it

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10
Q

difference between capillary and packed columns?

A

capillary much smaller diameter but a lot longer.

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11
Q

3 types of capillary columns?

A
  1. wall coated open tubular(WCOT)
  2. Support-coated open tubular(SCOT)
  3. porous-layer open tubular (plot)
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12
Q

what effect does mcreynolds constant have on the stationary phase?

A

higher the constant, the more polar the stationary phase

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13
Q

why is derivatization used in GC

A
  1. increases volatility, decreases polarity of analytes
  2. decreases thermal degradation of analytes
  3. improves detector response
  4. improves separation and decreases band broadening
  5. improve extraction efficiency
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14
Q

what are some disadvantages to derivatization in gc

A
  1. derivatizing agent can be difficult to remove and interferes with analysis
  2. can cause unintended chemical changes to analyte
  3. increases analysis time
  4. can cause extra response
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15
Q

what are the three types of derivatization in gc

A
  1. alkylation
  2. acylation
  3. silylation
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16
Q

how do you calculate resolution

A

difference of retention divided by mean of peak base widths

17
Q

explain plate theory

A

says that there are theoretical plates along a stationary phase. the more plates the more efficient the chromatography column is

18
Q

over what digit, does resolution be considered ‘valid’

A

over 1.5

19
Q

what three principles are considered for Rate theory

A
  1. eddy diffusion (A term)
  2. longitudinal molecular diffusion(B term)
  3. resistance to mass transfer in the liquid stationary phase (C term)
20
Q

draw out a diagram of a liquid chromatography apparatus

A
  1. mobile phase reservoir
  2. leading to pump beside injection valve.
  3. column followed by detector
  4. detector leads to waste and data recorder
21
Q

what force is required for LC

A

very high pressure

22
Q

what is the difference between normal phase and reverse phase HPLC

A
  • normal has a polar stationary phase(silica) and less polar mobile phase
  • reverse phase is, you guessed it, the reverse.
    reverse would use water or methanol as mobile.
    90% of time reverse phase is used
23
Q

suggest how you would manipulate the separation of HPLC

A
  1. change the composition of mobile phase (increase water content, increase organic modifier.)
  2. change polarity of the column
  3. heat the column
  4. derivatisation
24
Q

why is HPLC detection useful

A
  • used for quantitative and qualitative analyses.
  • analyzing peaks on a chromatogram
  • finding the identity of analyte(s) within each chromatogram peak. (detector selectivity)
25
Q

list three types of detectors and rank their selectivity

A
  1. mass spectral detection (MSD), the greatest selectivity
  2. UV & Fluorescence detectors, much better selectivity.
  3. Refractive index detectors. (RID) low selectivity
26
Q

how would you modify a system to enhance detector selectivity

A

derivitisation of analytes

27
Q

explain what a chromophore is

A

region in a molecule where the energy difference between 2 different molecular orbitals falls within the UV or visible spectrum

28
Q

explain pre-column derivatisation and why its done

A
  • analyte/sample undergoes derivatisation before separation on column
  • any reaction conditions can be made (time, temp, reagents)
  • however it might alter chromatographic properties like resolution or elution order of analytes
29
Q

explain post column derivatisation and possible disadvantages

A
  • occurs on-line between column and detector so doesnt affect resolution
    *disadvantages are:
  • might need to alter HPLC system to introduce reaction chambers
  • reaction conditions employed must be kept moderate
  • reaction must complete within 30 secs
30
Q

explain the layout of a CZE setup

A
  • capillary with tube diameter less than 1mm
  • filled with a running buffer
  • one end has a ‘destination vial’
  • other end has a source vial with an anode
31
Q

give a brief description of Electro Osmotic Force. ie. buffer, silica, interactions, layer

A
  1. capillary is made of fused silica so have Si-OH at inner surface
  2. running buffer above Ph 3 has OH minus ions
  3. these interact causing this eqn through de-protonation:
    Si-OH + -OH -> SiO- + H2O
  4. SiO- groups attract postive cations ie Na+ from buffer.
  5. this then forms a fixed layer held through non-covalent interactions, but is negative.
  6. a 2nd layer of cations form on fixed layer, which is deemed the mobile phase.
32
Q

why is CZE used as a form of chromatography

A
  • an electrically driven system is uniformly distributed along the capillary.
  • thus there is no pressure drop and velocity of flow is uniform.
  • this cause a lot less band broadening when viewed after detection

Medicine analysis and design (18 decks)

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