29. Chromatography And Spectroscopy

Question 1

What are the two phases of chromotography?

Answer 1

Stationary phase

Mobile phase

Question 2

What does chromatography do?

Answer 2

Seperate individual components from a mixture of substances

Question 3

What is the stationary phase (chromatography)

Answer 3

No movement

Normally a solid of liquid supported by a solid

Question 4

What is the mobile phase (chromatography)?

Answer 4

Moving phase

Normally a liquid or gas

Question 5

What applciations can chromatography be used for?

Answer 5

Drug analysis
Air samples
Forensic science

Question 6

What is thin layer chromatography?

Answer 6

A quick and inexpensive method of chromatography that indicates how many components are in a mixture

Question 7

What is the TLC plate made up of (chromatography)

Answer 7

Plastic or glass sheet coated w a thin layer of solid adsorbent substance-usually silica

Question 8

What adsorbent substance is usually used in TLC?

Answer 8

Silica gel

Question 9

What is the adsorbtion process in TLC?

Answer 9

The solid silica holds the different substances in the mixture to its surface

Question 10

How does seperation occur in TLC?

Answer 10

The different components have different affinities for the adsorbent so bind with different strengths to its surface

Question 11

Describe the steps to carry out TLC

Answer 11

1. Draw the base line on TLC plate 1cm away from end
2. Use capalliary tube to spot small amount of soloution of sample on base line
3. Place in either beaker w 0.5cm of solvent in and a watch glass on top / or use TLC tank
4. Allow solvent to rise until 1cm from top and immediately remove and mark solvent front
5. Allow to dry and circle spots

Question 12

What must we use to mark base line in TLC and why?

Answer 12

Pencil, insoluble so wont interfere with mobile phase

Question 13

What must we ensurewhne placing TLC plate in beaker and why?

Answer 13

that the solvent is under base line so sample doesnt dissolve in solvent soloution

Question 14

What can we do if spots appear invisible in TLC?

Answer 14

Shine UV light

Spray w iodine

Question 15

How do we interpret TLC results?

Answer 15

Each Component can be identified by Comparing retention factor values (Rf) with known values recorded for the same solvent and adsorbant

Question 16

Whats the formula to calculate retention factor values?

Answer 16

Rf=distance moved by component/distance moved by solvent front

Question 17

How can we compare samples visually?

Answer 17

Run pure samples of compounds that might be present along side unknown sample

Question 18

What is gas chromotography?

Answer 18

Used to seperate and identify volatile organic compounds present in a mixture

Question 19

What is the stationary phase in GC?

Answer 19

High boiling liquid adorbed onto an inert solid support

Question 20

What is the mobile phase in GC

Answer 20

Non réactive carrier gas such as helium or neon

Question 21

How does GC work?

Answer 21

• Volitile mixture injected into gas chromatograph
• moblie carrier carries sample through the capillary collumn which contains stationary phase
• the more soluble a component is the more it interacts with liquid stationary phase so the slower it moves
• this means components are sperated by solubility and reach detector at different retention times

Question 22

How can we identify components from retention times (GC)?

Answer 22

Compare to retention times for known components

Question 23

What does the area under a retention time peak tell us (GC)?

Answer 23

Peak intergrations can tell us the concentrations of componenents

Question 24

How do we determine concentration of a sample from its peak intergration?

Answer 24

• standard soloution of known concs of compound being investigated
• obtain gas chromatographs for each standard soloution
• plot calibration curve of peak area against concentration (external calibration)
• use callibration curve to measure conc of compound being investigated