chromatography

Question 1

what is chromatography used for?

Answer 1

to separate and analyse components in a mixture

Question 2

what is the mobile phase?

Answer 2

the phase that moves in chromatography

Question 3

what is the stationary phase?

Answer 3

the phase that does not move in chromatography

Question 4

how is the mobile and stationary phase separated in TLC?

Answer 4

adsorption to the plate /
solubility in the solvent

Question 5

how is the mobile and stationary phase separated in Gas chromatography?

Answer 5

relative solubility in the liquid stationary phase

Question 6

what is the stationary phase in TLC?

Answer 6

silica powder on a glass or plastic inert plate

Question 7

whats the mobile phase in TLC?

Answer 7

suitable organic solvent

Question 8

for TLC what results in a larger Rf?

Answer 8

-weaker adsorption between the component and the stationary phase so moves faster up the plate and larger distance
-the greater the solubility between the component in the mobile phase

Question 9

name the process by which TLC separates amino acids?

Answer 9

adsorption

Question 10

how is the TLC chromatogram analysed?

Answer 10

-calculating Rf value for each component
-comparing the Rf values to identify each component

Question 11

what is the formula of Rf

Answer 11

distance moved by component / distance moved by the solvent front

(small / big) should always be below 1

Question 12

give 2 limitations with TLC

Answer 12

-components with similar structures have similar Rf values so some components dont separate out
-difficulty in measuring accurate distances in the middle of the spot

Question 13

what is meant by Rf value?

Answer 13

distance moved by component / distance moved by solvent front

Question 14

what is gas chromatography useful for separating?

Answer 14

volatile components (low bp)

Question 15

what instrument does gas chromatography take place in?

Answer 15

a gas chromatograph

Question 16

what is in the stationary phase of gas chromatography?

Answer 16

a high bp liquid adsorbed on an inert solid support

Question 17

what is in the mobile phase of gas chromatography?

Answer 17

a carrier gas

Question 18

whats the separation method of gas chromatography?

Answer 18

solubility of the component in the liquid stationary phase

Question 19

whats in the capillary column?

Answer 19

a liquid stationary phase, adsorbed onto an inert solid

Question 20

what would make the component move slower through the capillary column?

Answer 20

if the component is more soluble on the liquid stationary phase

Question 21

define retention time

Answer 21

the time taken for a component to pass from the column inlet to the detector

units=s

Question 22

how is retention time used to identify unknown components?

Answer 22

the retention time is compared to retention times of known compounds

Question 23

in a chromatogram, what is the area under the peak proportional to?

Answer 23

the amount of the compound producing that peak. this is provided by the peak integration value

Question 24

give 2 limitations with gas chromatography

Answer 24

-compounds with similar structures have similar retention times so some components do not separate out
-new or unknown compounds have no known reference retention times for comparison

Question 25

give a method for determining the concentration of a component in a sample

Answer 25

-prepare standard solutions of known concentrations of the compound being investigated -obtain gas chromatograms for each standard solution -plot a calibration curve of peak against concentration -obtain a gas chromatogram of the compound being investigated under the same conditions -use the calibration curve to measure the concentration of the compound

Question 26

describe how a calibration graph could be obtained

Answer 26

1. prepare standard solution of unknown concentration 2. obtain gas chromatogram for each standard solution 3. measure peak area from integration value of the peak at ___minutes