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2nd year sem 1: spectroscopy and advanced analysis > Lecture 1: Fundamentals of gas chromotography > Flashcards

Lecture 1: Fundamentals of gas chromotography Flashcards

1
Q

what is extraction?

A
  • Isolation of analyte from a matrix

* Sample clean-up

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2
Q

what type of extraction is used for a gas and a liquid?

A

headspace analysis

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3
Q

when is liquid extraction used?

A

when your extracting from two liquids

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4
Q

what type of extraction is used when you have a solid and a liquid ?

A

chromatography

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5
Q

whats chromotography ?

A

A technique which allows the separation of a mixture of analyte molecules through their interaction with a stationary phase and a mobile phase.

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6
Q

whats a stationary phase?

A

The chromatographic phase (solid or liquid) that is held and through which the mobile phase moves.

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7
Q

whats a mobile phase?

A

The chromatographic phase that moves through the stationary phase, either a liquid or gas.

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8
Q

whats Eluent mean?

A

solvent entering a column or moving up a plate, becomes an Eluate when it leaves.

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9
Q

define elution?

A

process of passing a liquid/gas through a column

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10
Q

whats the Analyte/Solute?

A

the molecule undergoing separation.

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11
Q

what are the type of columns?

A

packed or open tubular

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12
Q

How are compounds separated in chromatography?

A

by means of their different affinity for a mobile

and stationary phase.

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13
Q

Analyte molecules _____ move between the ___ and

the ___ and interact with them.

A

continually
SP
MP

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14
Q

what is partition ( in C)?

A

the rate of movement of the analyte through the column is dependant upon the relative solubility of the analyte in the stationary phase and the mobile phase.

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15
Q

what is Absorption?

A

the relative polarities of the analyte and the stationary phase determines the rate at which the analyte moves.

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16
Q

why is gas chromatography sometimes sued?

A

to test the purity of a particular substance, or to separate the components of a mixture to determine the relative amounts of each.

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17
Q

GC is used on ____ analytes.

A

volatile

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18
Q

whats the mobile phase in GC?

A

moving gas

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19
Q

whats the stationary phase in GC?

A

a piece of glass or metal tubing called a column

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20
Q

what kin of samples can GC be used on?

A

sufficient volatility and thermal stability. should be volatile at around 400°C or below and do not decompose at these temperatures.

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21
Q

what happens first to the sample in GC?

A

instrument vaporizes a sample of the compound and transports it via a carrier gas into a column.

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22
Q

The components of the sample travel through the column at ___ _____ depending on their ____ ______.

A

varying rates

physical properties.

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23
Q

what happens second to the sample in GC?

A

eluted components enter a heated detector that generates an electronic signal based on its interaction with the component. A data system records the size of the signal and plots it against elapsed time to produce a chromatogram.

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24
Q

Compounds are separated by their different ____ to the column during the stationary phase.

A

affinities

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25
Q

Compounds with less affinity will elute from the column _____. compounds with greater affinity will elute ____.

A

sooner

later

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26
Q

what does GC seperate?

A

GC is used to separate polar and nonpolar compounds that are volatile.

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27
Q

where is GC applies?

A 
Food and flavor analysis
Environmental analysis
Industrial chemical analysis 
Petroleum industry analysis 
Forensic samples
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28
Q

what separation technique is better for non volatile compounds ?

A

liquid chromatography

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29
Q

Name some non volatile compounds?

A

proteins , salts and polymers

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30
Q

what does A gas chromatograph consists of (explain)?

A
  • A regulated and purified carrier gas source, which moves the sample through the instrument
  • An inlet, which also acts as a vaporizer for liquid samples
    • A column, in which the time separation occurs
    • A detector, which responds to the components as they elute from the column by changing its electrical output
    • Output: Data interpretation of some sort
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31
Q

what does A gas chromatograph consists of

A

gas source, inlet (sampler), column, detector and output

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32
Q

a carrier gas must be ?

A

pure

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33
Q

whats an example of carrier gases?

A

helium, nitrogen, hydrogen, or a mixture of argon and methane

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34
Q

what would happen if the carrier gas isn’t pure?

A

Contaminants may react with the sample and the column, create spurious peaks, load the detector and raise the baseline, and so on.

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35
Q

what does a carrier gas do?

A

transport the sample through the system.

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36
Q

what do detector gases do?

A

support certain detectors

37
Q

what supplies the gas?

A

Compressed gas cylinders or gas generators

38
Q

whats the most common inlets?

A

injection ports and sampling valves.

39
Q

what does an inlet do?

A

The inlet introduces the vaporized sample into the carrier gas stream.

40
Q

whats used to insert the sample through a septum into the carrier gas stream?

A

Liquid or gas syringes

41
Q

what allows for the amount of material injected to be regulated?

A

split outlet

42
Q

why are small sample sizes used in GC?

A

because Capillary columns have low sample capacities.

43
Q

what does a split mod injector allow you to do?

A

inject a larger sample, vaporize it, and then transfer only a part of it to the column.

44
Q

How does split mode work?

A

split valve remains open. The sample is injected into the liner, where it vaporizes. The vaporized sample divides between the column and the split vent.

45
Q

splitless mode is suited for what type of samples?

A

low concentration samples.

46
Q

what does a split less mode do to the sample?

A

traps the sample at the head of the column while venting residual solvent vapor.

47
Q

steps to splices mode

A

Step 1: Split valve closed, sample injected. The solvent (the major component) creates a saturated zone at the head of the column, which traps the sample components.
Step 2: Once the sample is trapped on column, open the split valve. The residual vapor in the inlet, now mostly solvent, is swept out the vent.

48
Q

what are the temps for splitless injection and split injection?

A

for splitless injection the temp is 220c , for split injection the temp is 350c

49
Q

which type of split/splitless injection involves a split vent?

A

split injection

50
Q

separations are ____ ___ dependent.

A

highly temperature

51
Q

what does it mean when the oven temp is ramped?

A

temperature is raised during run to elute all compounds

52
Q

when the oven temp is Isothermal it means?

A

temperature stays the same for run ( consistent)

53
Q

what happens during Temperature programming?

A

the temperature of column is raised during separation.

54
Q

whats a Typical temperature program?

A

– Initial oven temperature of 40-60°C,
– Hold 0 - 2 min,
– Raise temperature with 8-12°C/min to 220-280°C.

55
Q

As flow decreases it raises…

A

inlet pressure

56
Q

what is a capillary GC column composed of?

A

narrow tubing with a thin polymer coating

57
Q

Selecting the right capillary column is critical and depends on what factors ?

A

such as selectivity, polarity, and phenyl content.

58
Q

what does Column diameter influence?

A

efficiency, solute retention, and carrier gas flow rate.

59
Q

what does Column length affect?

A

solute retention, and costs.

60
Q

In gas solid chromatography what is the mobile phase and what is the stationary phase?

A
  • Mobile phase: gas (H2, He, N2)

* Stationary phase: solid (Charcoal, Mol. Sieves)

61
Q

In gas liquid chromatography what is the mobile phase and what is the stationary phase?

A
  • Mobile phase: gas (H2, He, N2)

* Stationary phase: liquid (very thin film

62
Q

after the column, the gas stream passes through what?

A

the detector

63
Q

what does the output form the detector become?

A

r becomes the chromatogram.

64
Q

what do detectors do?

A
  • Produce a stable electronic signal (the baseline) when pure carrier gas (no components) is in the detector
  • Produceadifferentsignalwhena component is passing through the detector.
65
Q

In GC how many common detectors are there?

A

7

66
Q

what are the GC detectors called?

A

Thermal conductivity detector
Flame ionization detector Electron capture detector Nitrogen-phosphorus detector
Flame photometric detector Atomic emission detector Mass selective detector

67
Q

what does a Thermal conductivity detector do?

A

Detects compounds with thermal conductivity that differs from carrier gas

68
Q

what does a flame ionisation detector detect?

A

Detects compounds that burn or ionize in a flame

69
Q

what does a Electron capture detector do?

A

Detects electron-capturing compounds (for example, halogenated compounds)

70
Q

what does a Nitrogen-phosphorus detector do?

A

Detects compounds that contain nitrogen and phosphorus

71
Q

what does a Flame photometric detector do?

A

Detects compounds that contain sulfur and phosphorus

72
Q

what does a Atomic emission detector do?

A

Tunable to many elements

73
Q

what does a mass selective detector do?

A

Identifies components from mass spectra (when combined with GC, the most powerful identification tool available)

74
Q

what does a Flame Ionisation Detector require?

A

requires Hydrogen and Air

75
Q

In FID ion production is ________ to

number of carbon atoms

A

proportional

76
Q

is FID destructive?

A

yes

77
Q

FID is a ______ detector.

A

universal

78
Q

FID can detect to as low as _____.

A

20pg

79
Q

Electron capture Detector is sensitive to?

A

compounds with a high electron affinity

80
Q

what does Electron capture Detector contain?

A

Contain radio-active 63Ni.

81
Q

ECD detects the..

A

constant current being measured, changes result in peaks.

82
Q

what is a chromatogram?

A

a graph

83
Q

what does a chromatogram plot?

A

abundance against time.

84
Q

what does the peak size on a chromatogram represent?

A

amount of compound in the sample

85
Q

what causes a large repack in a chromatogram?

A

As the compound`s concentration increases, a larger peak is obtained.

86
Q

what is retention time?

A

the time it takes of a compound to travel through the column.

87
Q

whats the retention time rule?

A

If the column and all operating conditions are kept constant, a given compound will always have the same retention time.

88
Q

what are the strengths of gas chromatography?

A
  • Easy to use • Robust
  • Many detectors
  • Low cost
89
Q

what are the limitations of GC?

A
  • Lack of confirming data other than retention time, except for mass spectrometer detection
  • Compounds must be thermally stable

2nd year sem 1: spectroscopy and advanced analysis (5 decks)

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