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FOSC301 > Gas Chromatography > Flashcards

Gas Chromatography Flashcards

1
Q

What is GC

A

analytical technique for the separation of a mixture of volatile compounds

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2
Q
A
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3
Q

what is the stationary phase

A

adsorbent phase

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4
Q

what properties must a compound have in order to be analysed using GC

A

sufficient volatility and thermal stability

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5
Q

range for GC oven temps

A

50-400C

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6
Q

components of GC

A

-Carrier gas supply
-inlet/ injection system
-column oven
-detector and data system

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7
Q

describe gas-solid chromatography

A

solid stationary phaseq

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8
Q

describe gas-liquid chromatography

A

Liquid stationary phase

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9
Q

In which phase do analytes move down the column

A

mobile phase

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10
Q

analytes are separated according to..

A

-affinity for the stationary phase
-analyte volatility

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11
Q

if a component has high vapor pressure and low solubility for the stationary phase describe the retention time

A

short

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12
Q

if a component has low vapor pressure and high solubility for the stationary phase describe the retention time

A

long

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13
Q

if a component has high vapor pressure and high solubility for the stationary phase describe the retention time

A

intermediate

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14
Q

if a component has low vapor pressure and low solubility for the stationary phase describe the retention time

A

intermediate

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15
Q

how do analytes elute from the column according to the distribution coefficient with respect to the stationary phase

A

in inverse order

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16
Q

variable parameters in GC

A

Stationary phase
-column selection for seperation according to polarity
Oven temperature
-seperate according to compound vapour pressure
Carrier gas and flow -type of gas, H or He
-affects resolution and speed of analysis

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17
Q

types of columns

A

polar or non polar

18
Q

types of polar columns

A

polyethylene glycol
free fatty acid phase

19
Q

retention time of a component with high vapor pressure and low solubility for stationary phase

A

short

20
Q

retention time of a component with high vapor pressure and high solubility for stationary phase

A

intermediate

21
Q

retention time of a component with low vapor pressure and low solubility for stationary phase

A

intermediate

22
Q

describe the components vapour pressure if the low and the solubility is high

A

long

23
Q

how can the vapour pressure be controlled

A

oven temperature program

24
Q

how can the solubility of a component to the stationary phase be controlled?

A

column selection

25
Q

what does increasing column length do to the system? advantages

A

increases efficiency and resolution

26
Q

what does increasing column length do to the system? disadvantages

A

increases band broadening and analysis time

27
Q

what is meant by the statement “the increase in resolution is not proportional to length”

A

the amount a column is increased does not = the amount of better resolution i.e. double length = 1.3 times better resolution

28
Q

what happens to column efficiency as the column diameter decreases

A

efficiency increases

29
Q

what is band broadening

A

the peak of gets wider

30
Q

how do different carrier gases affect a GC system?

A

change flow rate and velocities, therefore the speed of analysis

31
Q

carrier gases from best to worst

A

hydrogen> helium > nitrogen

32
Q

what does a GC detector do

A

measures the amount of a compound

33
Q

example of non-specific detectors

A

flame ionisation detector

34
Q

example of selective detectors

A

sulfur and nitrogen
mass selective detector (mass spec)

35
Q

how does a flame ionisation detector work

A

column effluent passes through flame and the flammable components are burned
-this combustion increases ions which generate an electrical current
-the current is amplified and measured

36
Q

advantages to a flame ionsiation detector

A

-signal intensity is proportional to concentration
-good linear range
-good for quantification

37
Q

disadvantages to FID

A

no structural info
no identification of compounds

38
Q

describe mass spec

A

the ionisation of gas phase molecules followed by the analysis of the masses of ion produced

39
Q

how does fragmentation occur in mass spec

A

electron impact ionisation

40
Q

how is the information from mass spec used

A

the fragmentations patterns can be compared to an MS database

41
Q

application of GC

A

food composition
flavor analysis
environmental analysis
medical application
forensic science
petroleum

42
Q
A

FOSC301 (17 decks)

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