Gas Chromatography

Question 1

What is GC

Answer 1

analytical technique for the separation of a mixture of volatile compounds

Question 3

what is the stationary phase

Answer 3

adsorbent phase

Question 4

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

Answer 4

sufficient volatility and thermal stability

Question 5

range for GC oven temps

Answer 5

50-400C

Question 6

components of GC

Answer 6

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

Question 7

describe gas-solid chromatography

Answer 7

solid stationary phaseq

Question 8

describe gas-liquid chromatography

Answer 8

Liquid stationary phase

Question 9

In which phase do analytes move down the column

Answer 9

mobile phase

Question 10

analytes are separated according to..

Answer 10

-affinity for the stationary phase
-analyte volatility

Question 11

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

Answer 11

short

Question 12

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

Answer 12

long

Question 13

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

Answer 13

intermediate

Question 14

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

Answer 14

intermediate

Question 15

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

Answer 15

in inverse order

Question 16

variable parameters in GC

Answer 16

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

Question 17

types of columns

Answer 17

polar or non polar

Question 18

types of polar columns

Answer 18

polyethylene glycol
free fatty acid phase

Question 19

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

Answer 19

short

Question 20

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

Answer 20

intermediate

Question 21

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

Answer 21

intermediate

Question 22

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

Answer 22

long

Question 23

how can the vapour pressure be controlled

Answer 23

oven temperature program

Question 24

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

Answer 24

column selection

Question 25

what does increasing column length do to the system? advantages

Answer 25

increases efficiency and resolution

Question 26

what does increasing column length do to the system? disadvantages

Answer 26

increases band broadening and analysis time

Question 27

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

Answer 27

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

Question 28

what happens to column efficiency as the column diameter decreases

Answer 28

efficiency increases

Question 29

what is band broadening

Answer 29

the peak of gets wider

Question 30

how do different carrier gases affect a GC system?

Answer 30

change flow rate and velocities, therefore the speed of analysis

Question 31

carrier gases from best to worst

Answer 31

hydrogen> helium > nitrogen

Question 32

what does a GC detector do

Answer 32

measures the amount of a compound

Question 33

example of non-specific detectors

Answer 33

flame ionisation detector

Question 34

example of selective detectors

Answer 34

sulfur and nitrogen mass selective detector (mass spec)

Question 35

how does a flame ionisation detector work

Answer 35

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

Question 36

advantages to a flame ionsiation detector

Answer 36

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

Question 37

disadvantages to FID

Answer 37

no structural info no identification of compounds

Question 38

describe mass spec

Answer 38

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

Question 39

how does fragmentation occur in mass spec

Answer 39

electron impact ionisation

Question 40

how is the information from mass spec used

Answer 40

the fragmentations patterns can be compared to an MS database

Question 41

application of GC

Answer 41

food composition flavor analysis environmental analysis medical application forensic science petroleum