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Synthesis of drugs > chromatography > Flashcards

chromatography Flashcards

1
Q

what is chromatography

A

method of separation, components separated are distributed between 2 phases (stationary and mobile)

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2
Q

general concepts- how are samples loaded

A

sample introduced in small volume (at inlet of column or another carrier of the stationary phase)

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3
Q

general concepts- elution
-what is it

A

mobile phase (eluent) transports sample component in contact with stationary phase, due to different interactions between sample and stationary phase the sample migrates at different speeds and elute from the system at different retention times

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4
Q

general concepts- detection
-how are compounds visualised

A

compounds visualised when they elute out of system, visualisation done by UV-vis, fluorescence, refractive index, evaporative light scattering detectors

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5
Q

what causes different retention time

A

different interactions between sample components and stationary phase

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6
Q

types of chromatography

A

TLC, size-exclusion, reverse-phase, ion exchange, gas chromatography

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7
Q

what is TLC ,its typical stationary phase ,its plate backing support and how is the sample loaded

A

thin layer chromatography

typical stationary phase- SiO2, Al2O3
typical TLC plate backing support- glass, aluminium, plastic

spot sample on line with capillary tube

(the one done in a beaker and lid)

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8
Q

how to calculate Rf value in TLC

A

Rf=distance travelled by sample/distance travelled by solvent front

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9
Q

how are samples detected in TLC

A

under UV or visible light after elution, may need staining

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10
Q

name 3 universal stains

A

KMnO4, cerium ammonium nitrate, iodine

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11
Q

name 2 functional group specific stains

A

ninhydrin- primary/secondary amines

dinitrophenylhydrazine (DNP)- aldehydes, ketones

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12
Q

what stain is specific for primary and secondary amines

A

ninhydrin

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13
Q

what stain is specific for aldehydes and ketones

A

dinitrophenylhydrazine (DNP)

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14
Q

describe the basic mechanism of chromatography

A

mobile carrier phase flows over supported stationary phase, solute molecules move back and forth between stationary and mobile, presence in stationary phase decreases the rate which they are carried by mobile phase

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15
Q

in SiO2 chromatography what are the common interactions between analyte and stationary phase

A

hydrogen bonds, dipole dipole, VDW

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16
Q

compare the interactions with the stationary phase between polar and non polar compounds

A

polar compounds interact more strongly with stationary phase so it moves less

nonpolar interacts more weakly, moves further

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17
Q

how to compare TLC with column chromatography

A

same stationary phase= same principles
polar compounds interact stronger than non polar, polar move less quickly through the column, the product that runs faster in TLC (non polar) will be eluted from column first

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18
Q

what increases Rf value

A

increased polarity of mobile phase

19
Q

how does a mixture of products get separated into components in chromatography

A

sample has some components that interact stronger so move slower, components that interact weakly will move faster, different rates cause separation

20
Q

advantages and disadvantages of TLC

A

advantages- quick, simple, low tech, cheap, little training needed

disadvantages- chemical nature of compounds must be confirmed with other techniques, qualitative

21
Q

how does flash chromatography work

A

uses compressed gas (eg. nitrogen) to push solvent through column, uses finer particle size for stationary phase (eg. silica gel)

(kind of like column ig)

22
Q

what does HPLC stand for, what is it and how does it work

A

high performance liquid chromatography

highly improved form of column chromatography, solvent forced through under high pressure

23
Q

how can results be detected

A

UV-vis, fluorescence, MS, refractive index, evaporative light scattering

24
Q

what is retention time
(tR)

A

time taken for solute to pass through a chromatography column, calculated as time from injection to detection

25
Q

what is total retention volume (VR)

A

volume of mobile phase entering column between sample injection and emergence of peak maximum of sample component of interest

26
Q

how to calculate retention time

A

tR=VR/Fc

Fc=mobile phase flow rate
tR=retention time
VR=total retention volume

27
Q

what is the number theoretical plates (N)

A

indicates how efficiently a column can separate a mixture of products into its individual components

28
Q

how to calculate number of theroretical plates from a graph

A

N=16(tR/Wb)^2

retention time= measured from 0 to intersection of tangents

width of triangle base= measured where tangent intersect with x axis

(pic on one note)

29
Q

describe the results of the number of theoretical plates (N)

A

narrower base=more efficient=greater N value

wider base=less efficient=smaller N value

30
Q

what is size exclusion chromatography work and what is it used for

A

separates different compounds according to the size in solution

used for analysis/purification of macromolecules

31
Q

when the stationary phase of a size exclusion chromatography is a swollen gel what is it called

A

gel permeation chromatography

32
Q

what is gel permeation chromatography

A

size exclusion chromatography but with swollen gel as the stationary phase

33
Q

describe the stationary phase in size exclusion chromatography

A

stationary phase are porous beads

34
Q

how does size exclusion chromatography work

A

size of molecules in sample determine whether they enter pores of poruous beads, larger molecules (higher MW) will not enter the pores so it will have a shorter elution path and be the first eluted from the column, smaller molecules will follow the shape of the pores so it has a longer path and therefore be eluted last

35
Q

what is reversed phase chromatography and how does it work

A

stationary phase has hydrophobic groups instead of polar ones (also in a column)

separation of molecules based on hydrophobicity, hydrophobic compounds interact more strongly with stationary phase than polar compounds

(nonpolar compounds go slower i think)

36
Q

uses of reversed phase chromatography

A

sample analysis and purify large amounts of compounds

37
Q

why is normal phase chromatography often preferred

A

analytes to hydrophobic/phillic for reversed phase, for purification of products on a lab scale

38
Q

difference between normal phase and reversed phase chromatography

A

normal phase- stationary phase is polar and mobile is non polar
-polar molecules interact strongly so move less

reverse phase- stationary phase is non polar, mobile phase is polar
-nonpolar molecules travel further

39
Q

what is ion exchange chromatography

A

separates compounds based on overall charge, limited to purification of ionisable molecules

40
Q

how does ion exchange chromatography work

A

charged molecule binds to a oppositely charged stationary phase

stronger charge will bind more strongly so it will elute last, weaker charge elute first

41
Q

types of ion echangers

A

anion exchangers
quaternary ammonium- strong
protonated tertiary amines- weak

cation exchangers
sulfonic acid salts- strong
carboxylates- weak

42
Q

what is gas chromatography

A

separation technique carried out in a column where the mobile phase is gas, used to isolate volatile components

43
Q

how does gas chromatography work, what mobile phase and stationary phase is used, how it it detected

A

analytes vapourised to be injected

mobile phase- inert gas carrier (He,N2, Ar)

stationary phase- solid adsorbent or liquid on inert support

detection- flame ionisation detectors/ thermal conductivity detector/ mass spectrometer

Synthesis of drugs (9 decks)

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