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Flashcards in Gas Chromatography Deck (50)
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1

IUPAC definition of gas chromatography:

separation technique; mobile phase is gas (carried out in column)

2

The analytes in GC must be _____. Otherwise, they may be ______ in order to be compatible.

gaseous/vaporizable (volatile or semi-volatile)

derivatized (modify into structure that is volatile)

3

What are common mobile phases for GC?

inert gas (He, argon, N2)

4

What is the stationary phase for GC?

LIQUID or solid phase immobilized in column

(gas-solid chromatography has limited applications - not common)

5

Gas-_____ chromatography is the most common technique. Describe it.

gas-liquid

liquid (NON-VOLATILE) stationary phase adsorbed onto solid inert packing or immobilized on capillary tubing

separate compounds based on volatility + interaction w/ stationary phase

6

GC separates compounds based on ____ and _____

volatility (vapor pressure)
interaction with stationary phase (partitioning)

7

Basic parts of a GC: (6)

carrier gas flow control
injection port + heater
separation column w/ stationary phase
oven
detector + data recording

8

What is the usual flow rate in a packed GC column?

25-150mL/min

9

What is the usual flow rate in a open tubular GC column?

1-25mL/min

10

What is the usual pressure of the inlet?

10-50 psig

11

common injection modes for liquid samples for GC:

injection with microsyringe (manual or autoinject)

12

common injection modes for solid or liquid (or SPME) samples for GC:

thermo-desorption unit: heat sample for desorption of volatiles

13

2 main parts of the injection port for GC:

rubber septum (needle inserted thru)

glass insert (vaporization chamber)

14

T/F: temperature does not matter for the injection port

False; usually maintained at high temp

15

The different types of injections:

1. split injection
2. splitless injection
3. on-column injection

16

What is a split injection? What is it used for?

only small fraction (0.1-1%) of injected will actually enter column (rest is waste)

used for routine analysis/high concentration samples

17

What is splitless injection? What is it used for?

all injected sample moves into column

for quantitative analysis of trace analytes

18

what is on-column injection? what is it used for?

NO HEATED injection port (low temperature to condense sample in narrow band)

for samples that decompose above boiling point (temp sensitive)

19

____ can be used to directly absorb analytes from the sample headspace, and inject to ____ into GC

headspace SPME
desorb analytes

20

2 main types of columns for GC:

packed columns
capillary columns

21

Describe the typical GC packed column (materials, dimensions)

materials: glass or stainless steel
dimension: 1-5m length, 5mm inner diameter

filled/coated w/ stationary phase

ex: C based (carbotrap, carbopack, carboxen); zeolite (aluminosilicate); synthetic polymers (tenax, chromosorb); silica/alumina

22

examples of typical GC packed columns:

C based (carbotrap, carbopack, carboxen)
zeolite (aluminosilicate); synthetic polymers (tenax, chromosorb);
silica/alumina

23

Describe the typical GC capillary column (materials, dimensions)

thin fused-silica (purified silicate glass)

10-100m length, 250um inner diameter

stationary phase coated (few um) on inner surface

24

capillary GC columns have a (thin/thick) coating on the inner surface. This allows for a (slow/fast) equilibrium between ___ and ____

thin
fast
mobile vs stationary phaes

25

What is WCOT and SCOT?

coating types in capillary columns:

WCOT: wall coated open-tubular (column coated w/ liquid)

SCOT: support-coated open-tubular (porous support coated w/ liquid)

26

T/F: a packed column is shorter than a capillary column

True

27

Which has a smaller diameter, a packed or capillary column? How does this affect flow rate?

capillary
slower flow rate (10-60mL/min vs 0.5-15mL/min)

28

T/F: a capillary column can be up to 100m in length

True

29

T/F: the column head pressure can be similar in packed vs capillary column

True; but capillary column range can be lower (10-40 vs 3-40 psig)

30

Which has a higher theoretical plate #? packed or capillary column?

capillary

31

Which can tolerate a higher sample load? packed or capillary column?

packed

32

the stationary phase in GC is a non-____ liquid coated on a ______

volatile (and inert)
solid support

33

Give some common examples of GC stationary phases

polydimethyl siloxane (gen purpose)
5% phenyl-PDMS
50%phenyl-PDMS
50% trifluoropropyl-PDMS
polyethylene glycol
50% cyanopropyl-PDMS

34

A 100% polydimethyl siloxane coating is (polar/nonpolar)

nonpolar

35

What effect does increasing % of phenyl groups on polymer PDMS achieve?

increases polarity

36

polyethylene glycol is used for (polar/nonpolar) compounds

polar

37

what stationary phase is used to analyze FAMEs?

5% phenyl-PDMS

38

what stationary phase is used to analyze drugs or steroids?

PDMS or 50% phenyl-PDMS

39

what stationary phase is used to analyze PUFAs?

50% cyanopropyl-PDMS

40

For what compounds is PEG used as a stationary phase to analyze?

free acids, alcohols, ethers, essential oils, glycols

41

___ GC columns have been developed for enantiomer separation, which is important in the ____ industry

chiral
pharmaceutical (different enantiomers have different physiological activity)

42

chiral stationary phases use derivatives of: (3)

cellulose
chiral silane
cyclodextrin (B-cyclodextrin - a 7 sugar ring molecule)

43

The separation column in GC is usually conducted inside a ______. Why?

thermostat-controlled oven

partitioning mechanisms are dependent on temperature

44

What is the usual temp range of the liquid gas (CO2) vs the oven?

liquid gas: -50C
oven: 400C

45

Why is precise temperature control of GC oven important?

will determine the separation precision

46

Compounds with what functional groups cannot be analyzed directly with GC? Why?

functional groups with active hydrogens (COOH, OH, NH, SH)

tend to form intermolecular H bonds -> lower volatility + interact w/ column material

47

What can be done to make compounds containing active H groups compatible with GC?

derivatization (modify property of compounds)
alkylation
acylation
silylation

48

T/F: fatty acids are directly analyzable with GC

False; need to convert into FAMEs

49

What are FAMEs?

fatty acid methyl esters (derivatized fatty acids)

FA + BF3/methanol -> methyl FA

50

derivatization will lower the _____ of a compound

boiling point (vapor pressure)