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Chem 220 - Analytical Chemistry > Chromatography > Flashcards

Chromatography Flashcards

1
Q

define chromatography

A

physical method of seperation in which the components to be separated are distributed between two phase, mobile and stationary. it separates molecules based on difference in heir structure and or composition

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2
Q

define teh stationary phase

A

the phase that stays fixed inside the column. Can be either a solid or a thick and sticky liquid, that is bound to solid particles of the inside wall of the colum

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3
Q

define the mobile phase

A

the phase moving through the column. this can either be a liquid or a gas.

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4
Q

what is the difference between liquid and gas chromatography?

A

liquid: mobile phase is liquid
gas: mobile phase is a gas

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5
Q

define eluent

A

fluid that is entering the column. ent = enter

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6
Q

define eluate

A

fluid that is exiting the column

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7
Q

define elution

A

the process of passing a liquid or a gas through the column

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8
Q

waht are the 4 kinds of chromatography

A

adsorption, partition, ion exchange, pore penetration

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9
Q

define adsorption chromatography

A

this is when you use a solid stationary phase and a liquid or gaseous mobile phase. The solute is absorbed on the surface of the solid particles.

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10
Q

define partition chromatography

A

this involves a thin liquid stationary phase coated on the surface of a solid support. Solute equilibrium is between the stationary liquid and mobile phase

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11
Q

define ion-exchange chromatography

A

Anions or cations will covalently attach to the stationary solid phase, which is a resin. the ions will attach to the stationary phase by a electrostatic force. Mobile phase is a liquid

think of example with stacey being the resin, negative, and her kids being cations and attaching to her. Each kid will be attracted to the negative charge in different ways and their strength will differ.

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12
Q

define molecular exclusion chromatography

A

this is where the molecules are separated by size, the stationary phase and solute have no interaction with each other. the stationary phase has pore, different sizes, that will capture the smaller moelcules, allowing for the alrger molecules to pass through.

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13
Q
A
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14
Q

define affinity chromatography

A

this is the most selective kind, where there are specific interactions between one kind of solute molecule and a second molecule that is covalently attached to the stationary phase.

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15
Q

define chromatogram

A

this si what will show the detectors response 9arbitrary unit, AU) as a function of time

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16
Q

define retention time

A

it is the time needed after injection for a solute to reach the detector, Tr

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17
Q

what is Tm

A

it is the time required for the mobile phase to travel through the colum

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18
Q

what is T’r

A

it is the actual retention time for the solute to travel through the column, this is equal to the difference bettwne Tr and Tm

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19
Q

define seperation factour

A

measure of the relative retention of analytes

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20
Q

define retention factour, k

A

it describes the time spent by the compound in the stationary phase as opposed to the mobile phase, the larger the compound, the larger the k value

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21
Q

define theoretical plates

A

it is a discrete section in which a solute molecule equilibrates between the mobile and stationary phases. they are a measure of the efficiency of a column. high efficient need a large number of plates. can use width or half width to determine this value. can determine the height o the plate by diving the length of the comlum by the # of theoretical plates.

think of how big a step size can be. the larger the step, the more energy it will take to climb them versus is the size was smaller, it would take a lots less energy.

22
Q

define resolution

A

it is the space between adjacent peaks, the more space between two peask, the higher the resolution. (more space = more resolution)

it is a measure of the ability of a column to separate two peaks. (baseline resolution)

23
Q

what are the 3 ways you can broaden your band in a column?

A

diffusion, multiple flow paths, and mass transfer between phases

24
Q

explain diffusion to broaden bands

A

Solute molecules will diffuse away from the centre in both direction, called longitudinal diffusion. with a faster flow rate, the band spends less time in the column and therefore less time for diffusion to occur.

increase flow to get a sharper peak

25
Q

explain how multiple flow paths can broaden bands

A

borading occurs due to irregular and multiple flow paths on column, called eddy diffusion. Example fo stacey moving in different lanes, but each lane has different obstacles to overcome making the band braoden as the time taken for each molecule is different.

26
Q

explain how mass transfer between phases can broaden bands

A

If solute cannot equilibrate quickly enough between mobile and stationary phases, solution tends to lag behind the solute in mobile. tis is observed if equilibrium between the phase is slow and or the flow is too fast. Slow rates with minimize band broadening.

think of Stavey trying to hold onto something but her body is being stretched out and some of her with reach the ned of the column before the rest of her does.

27
Q

how do we determine an optimal flow rate?

A

we need to experiment with such conditions as flow rate, compositions, and temperature to obtain the best separation between analytes in the mixtures.

28
Q

define qualitative analysis in chromatography

A

identifying susbtances based of off their retention time

29
Q

define quantitative analysis in chromatography

A

the area of the peak is proportional to the quantity of that component peak

30
Q

what is the difference between an internal and external standard in calibration?

A

external: used to quantitatively determine teh concentration of an unknown sample. Standard are obtained and the peaks are plotted as function of concentration

internal: standard is added to same substance as the analyte. standard is different than analyte. use for analysis in which the quantity of sample analyze or response varies between sample measurements

31
Q

define HPLC

A

high-performance liquid chromatography
- uses high pressure to force eluent (entering) though the closed column packed with micron sized particles

essential parts:
-solvent delivery system
- sample injection valve
-column
-detector
-signal processing readout

32
Q

explain all the essentail parts of an HPLC machine

A

-solvent delivery system: needs to be blend of 2+ solvents, can determine overall polarity
- sample injection valve: special valve is required in order to inject the sample into the column
-column: main column is protected by guard column (protects from irreversible adsorption and impurities)
-detector: Ultraviolet (light that passes from source is measured), refractive index (each solute has specific index, measures deflection of light in eluate), fluorescence (only response is analyte has fluorescence, irradting the eluate and monition emmison wavelength)
-signal processing readout

33
Q

what are the 2 types of elution in HPLC?

A

isocratic: solvent composition in unchanged furing process, more time efficient

gradient: solvent composition changes

34
Q

explain the stationary phase in HPLC?

A

most commin is silica. A liquid pahse is either coated or chemically bonded on a solid support. the components of the solution will migrate according to the non-covalent interactions of the components in stationary phase.

normal phase: stationary is polar, mobile is non-polar, least polar with elute first follower by most polar going last

reverse-phase: is the reverse of normal

35
Q

define derivatization

A

process of attaching an easily detectable group to the analyte

36
Q

define gas chromatography

A
  • gaseau mobile phase transports gaseous solute through thin long column
    -used for organic compounds
  • sample is converted to vapour state by injecting it into heated port
  • maintained at temp above boiling point
  • trasnported by carrier inert gas
  • detector is maintained at higher temp than column
37
Q

define carrier gas of GC

A
  • chemically inert: not reach with anything
  • high purity: no water or oxygen
  • detector compatibility
  • economic adn safety
  • efficeny and speed
38
Q

define sample injection port of GC

A

sample is injected with syringe into heat port where sample then vaporizes.

split: substantially reduce amount of sample that is injected into colum, not used often for quantitative
splitless: better for quantitative analysis, port gets maximum amount of sample onto the column, gas flow is initally turned off until sample is fully in GC machine, then turned on.
on-column: for sensitve compounds that decompose above boiling temperatures, solution is directly put into colum wihtout injection port, column is at temp that is below boiling, trapping analyte to produce narrow band

39
Q

what are the kinds of columns you can use in GC?

A

packed: tends to give greater quantitative accuracy and precision, filled with small particles that are coated with a stationary phase

capillary: typically give better seperation because they dont have multiple path band broadening, much longer, smaller plate height, higher resolution, stationary phase is coated on internal wall of column

40
Q

what are teh 3 kinds of capillary columns?

A

WCOT: walls are coated with liquid stationary pase

SCOT: inner wall of the capillary is lined with a thin layer of support materials (such as fused silica)

PLOT: inner wall of the capillary is lined with a thin layer of porous support material, similiar to SCOT

WCOT>SCOT>PLOT for resolution efficiency

SCOT AND PLOT are generally less efficient than WCOT

41
Q

how is column temperature controlled?

A
  • must be controlled within a tenth of a degree
  • optiomal colum temp is dependent upon boiling point of the sample
  • minimla temps ive god resolution but increased elution times

temperatuer programming:
- colum temp is raised during the seperation
- allows the seperation of compounds with a wide range of boiling points and polarites
- temp increases and seperation increases

42
Q

what are the types of detectors in GC?

A

non-selective: responds to all compounds except carrier gas
selective: responds to range of compounds with common phy. or chem property
concentration dependent: signal is related to concentration of analyte and doesnt destroy the sample
mass flow: destrop the sample, signal is realted to the rate at which analyte molecules enter the detector

43
Q

define solid phase microextration

A

SPME integrates sampling, extraction and preconcentration all in one by using a small fused-silicia fibre coated with a polmeric stationary phase, usually PDMS.

44
Q

what are the advantages and disadvantages of SPME?

A

advantages:
- elimination of solvent
- simplicity
- versatility
- can be used for large variety of analyte

disadvantages:
- fragility of coated fibre
- low sorbent reading
- run to run variability
- bending of the syringe during operation
- instability and swelling pf PDMS coating organic solvents
- short lifetime of sorbent coating

45
Q

Define detectors

A
  • mainted at elevated temp to prevetn condensation of analyte

non-secletive:responds to range of compounds except carrier gas
selective: all compounds with common physical/chemical component
specific: only a single chemical compound

46
Q

what are teh 2 main groups of detectors?

A

concentration-dependent: related to the concentration of analyte in the detector and does not destroy the sample

mass flow dependent: destroys sample and the signal is related to the rate at which analyte molecules enter the detector

47
Q

what are the specifications for an ideal detector?

A
  • adequate sensitivity
  • stability and reproducibility
  • linear response
  • temperature range to cover all boiling points
  • short response time
  • high reliability and ease of use
  • similarity response towards all analytes
  • non-destructive of sample
48
Q

define thermal conductivity detector, TCD?

A
  • measures ability to transport heat from hot to cold region
  • gas is passed from heated filament wire
    -temp and resistance of wire with vary depending on thermal conductivity of gas
  • as electrical resistance of wire change, change in voltage is measured
49
Q

define flame ionization detector, FID?

A
  • elute is burnde in a mixture of H and air
  • carbon atoms produce CH to produce CHO ions
  • the ions produced with be collected by pair of opposing change electrons
  • only 1 in 10000 atoms produce electrons
  • less sensitive compared to TCD
50
Q

Define electron capture detector?

A
  • gas entering detector is ionized by high energy electrons emitted y foil with Ni
  • electrons are let go from gas attach to anode and produce steady current
    -analytes molecules will enter detecots and can capture some of the electrons to reduce current
  • decrease in current is the signal
  • good for highly electronegative compounds
51
Q

what are other detectors used?

A

-flame photometric
- alkali flame
- sulfur chemiluminescence

52
Q
A

Chem 220 - Analytical Chemistry (10 decks)

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