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Quality Control > Gas Chromatography > Flashcards

Gas Chromatography Flashcards

1
Q

Definition of GC

A

A tool for the sepration of compounds in mixtures based on the polarity of compounds

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2
Q

What’s the preresiquite for GC

A

GC is for compounds that are volatile or that can be made volatile on derivationzation

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3
Q

On what does the separation of compounds depends on?

A

it depends on the partitioning behaviour difference between mobile and stationary phase

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4
Q

what happend in at the SP?

A

Sample gets adsorbed in the SP of the column, which is seperated by the carrier gas

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5
Q

What’s the property of the carrier gas?

A

iner gas either helium or nitrogen

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6
Q

What has to be done with liquid sample before injection?

A

There have to be vaporied

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7
Q

On what does the elution depends?

A

it depends on the polarity of the compounds

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8
Q

What does the response of the GC means?

A

it is proportional to the concentration of the analyte in the introduced sample

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9
Q

Which kind of detector can be used for Residual solvent Analysis?

A 
Flame ionization (FID)
thermal conductiveity detecor (TCD)
Mass spectrometery (MS)
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10
Q

Where can GC be used in the pharmaceutical field?

A

Residual solven analysis, analysis of various functional groups
percentage of purity of pharmaceutcail compounds
identification of impurities

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11
Q

Which other detectors can be used for identification of specific functional groups

A

IR, UV, MS

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12
Q

Disadavantage of GC?

A

applicable ony for volatile compounds

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13
Q

How does the flam ionisation detector works?

A

it detects the amount of inos release from the combustion of a sample in ahydrogen falme which is proportinal to the amout or organic compound present in the ignited

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14
Q

what is the column velosity?

A

it describe how quick the chromatography will take place and how the column can resolve the peaks efficiently.

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15
Q

What does higher velocities means?

A

it means the chromatogrma will be produce faster compared to a low velocity

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16
Q

On what does the velocity value depends on?

A

it depends on the column charateristics, sample temperature, carrier gas

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17
Q

what is the carrier-gas flowrate?

A

it describe how well the colume suits the hardwars as its entrance and exit

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18
Q

What happend when the sample is not well delivered to the coulmn

A

it can lead to peak distortion, at too high or too low column

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19
Q

what affects the separation efficiency?

A

the chose of carrier gas and linear velocity

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20
Q

What does is mean, when the temperature is kept constant

A

one has a isocratic elution process

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21
Q

Learn how to draw the GC

A

Do you know how to do it?

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22
Q

Why it is important to know the boiling point of the samples?

A

Compound with higher boiling point will have higher affinity to the stationaty phase

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23
Q

Which interaction between the compounds and SP can occur

A

Hydrophobic interaction (van der waals forces

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24
Q

How does the increase of carbon chain affect the polarity of alcohols?

A

increase in the length of the hydrocarbon chane, decrease the hydrophilicity of the whole molecule.

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25
Q

How are the components sepearted?

A

the volatile analytes of the mixture are separated through differences in boiling points and retention time in terms of vapor pressures and distribution coefficient

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26
Q

example of mobile phase

A

inert carrier gas like helium,hydrogen or nitrogen

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27
Q

different between the inert gases

A

Hydrogen gas is used for short analysis time, higher flow rate can be achieved

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28
Q

explain the two types of cappilary columns

A

non-polar column, longer, higher diameter and film thickness

polar column, shorter length, narrower diameter and thinner film thickness

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29
Q

what affects the volatility?

A

vapor pressure (boiling point), solubility and interaction in the SP

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30
Q

the vapor pressure changes the

A

equilibrium betwen MP and the SP if specific interactions occur

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31
Q

what’s the fundamental paramter in the GC

A

retention time. it is the time measuremnet for solutes to pass through the colume from injection to detection

32
Q

other various important parameters are

A

retention factor, peak area, peak height and peak form

33
Q

on what does the seperation time is based

A

on the time spent in the mobile phase and in the SP

34
Q

how does the molecular weight and the bond strength influence the RT

A

it increases the Rt in the stationary phase

35
Q

how can the retenion time be reduced?

A

by increasing the capillary temperature

36
Q

what’s the ad von a temp. gradient?

A

it can strengthen the seperation efficiency from a mixture of analytes with varying boiling points

37
Q

whats the phase ratio

A

it is the ratio of the column inner diameter and the SP film thickness
low phase ratio–> high value of retention factor with broad peak

38
Q

importance of the column length

A

have to be considered inorder to achieved high separation efficiency and short retention time

39
Q

factors that influence the separation are

A

vapor pressure, boiling tempertaure, polarity, column temperature, carrier gas flow rate, amount of material injected and column length

40
Q

what’s the benefit of FID?

A

it reacts to all hydrocarbon gases like alcohol and has a broad varity of measurement

41
Q

Which gases can the FID not detect?

A

non burned gases like h20, c02, s02, nox and noble gas

42
Q

what’s the optimal separation

A

peaks are away from each other and as narrow as possible

43
Q

what’s the plate height?

A

it is the constant of proportionality between the variance of the band and the distance it has traveled

44
Q

plate height can also be describe as?

A

the length of a coulmn required for one equilibration of solute between the MP and SP

45
Q

how does the plate height affects the bandwidth

A

if the plate height is small then the bandwidth is narrow

46
Q

what happend if the column has more theoretical plates?

A

the separation is better

47
Q

which equation can be used to describe the separation efficacy

A

the van deemter

48
Q

what happend to the PH if the flow rate is increased?

A

the plate height is decreases, because compounds have stay less time inside the column and their longitudinal diffusion will be less

49
Q

What is important while injecting the samples?

A

it should be injected carefully and fast, leading to a narow bandwidth from the injection

50
Q

what causes broad bands?

A

when one component would stick in the SP

51
Q

What’s the relation between the thickness of the SP and the plate height?

A

Reduction of the thickness of the SP it leads to reduction of the plate height, because of faster diffusion of the compound from the SP, far fom the SP and inside the MP

52
Q

What’s the relation between the radius and the plate height?

A

small radius, leads to decrease of the PH, due to the reduction of the travel distance of the component

53
Q

How does an increase of the temp influnece the diffusion coefficient?

A

increase of the temp, leads to an increase of the diffusion coefficient

54
Q

what’s the benefits of GC?

A

bozj qualitative (identification of individual components) and quantitative (concentration of particular components)

55
Q

what’s important during a quantitative anaylsis

A

creation of a calibration curve

56
Q

What’s the main different in the carrier gas used in GC

A

it does not undergo interactions with analyte itself

57
Q

How is the componten divided during GC-process

A

the non-polar component ratain on the SP, while the polar are carrier through the column

58
Q

Why is the column temperature mainted in a higher degree

A

inoder to maintain the compound in the gas phase and to reduced the retention time

59
Q

what influences the RT?

A

interaction of the compound in SP and higher solubility of the compound (increases the RT)
increase of column length, also increase the RT as well as the resolution

increase of temp, decrease the RT, due increase of the kentic energy which decrease the solubility of the compound

increase of the Flow Rate, we increase the rate at which the mixture moves, thus decreasing the RT

60
Q

What affects the retention factor

A

higher impact has the film thickness , compared to the inner diameter of the column

61
Q

How does the film thickness affect the RF

A

extremely volatile compounds, a thick film colum should be used to increase the retention, whereas if one is analyzing high molecular weight compound, a thinner film should be used

62
Q

Thicker and thinner film

A

Thinner film, reduction of the retention, compared to the thicker film

63
Q

Inner diameter and the RF

A

smaller inner diamter produces higher retention compared to larger ID column

64
Q

why do small ID leads to higher RF

A

it is due to the less available mobile phase volume in the column

65
Q

what are the ad and disad von longer and shorter column in GC

A

Longer column provide more resolving power, but increase analysis time

66
Q

Which factor is most influence by the column length?

A

the retention factor has the greates effect on resolution

67
Q

what happend if the column length is doppelt?

A

it increases the resolution as well as the retention time

68
Q

larger and smaller ID incomparison to their peaks?

A

smaller ID columns generate more plates per meter and sharper peaks, leading to better separation efficiencies

69
Q

When should smaller ID be used?

A

When more complex samples need to be analyzed

70
Q

when is the disad von smaller ID?

A

loading capacities are lower

71
Q

what could be the cause of a poor resolution?

A

Non-selective SP
Poor efficiency
Sample overlaod
Incorrect analytical condititions

72
Q

what could be the cause of a poor retention time

A

Resolution/integration issues
incorrect column/oven temperature
injection daly between pushing start and actual injection, if manual injected

73
Q

Cause for an split peaks

A

Incomplete vaporization

Sample loading capacity exceeded

74
Q

cause for unstable baseline

A

Carrier gas leak or contamination

injector or detector contatmination

75
Q

cause for Broad peaks

A

low flow rate
column film is too thick
slow GC oven program

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