chromatography and spectroscopy

Question 1

mobile phase

Answer 1

the phase that moves in chromatography

Question 2

stationary phase

Answer 2

the phase that doesn’t move in chromatography

Question 3

thin layer chromatography

Answer 3

mobile phase = solvent
stationary phase = silica mounted on glass plate
separation method = adsorption

Question 4

adsorption

Answer 4

how well a component sticks to the stationary phase
the stronger the adsorption between the component and the stationary phase, the slower the component moves up the plate
the more soluble a component is in the solvent, the faster it moves up the plate

Question 5

retention factor

Answer 5

distance moved by component / distance moved by solvent front

Question 6

limitations of TLC/GC

Answer 6

components with similar structures have similar Rf values so don’t separate out

Question 7

gas chromatography

Answer 7

mobile phase = carrier gas
stationary phase = liquid adsorbed on an inert solid
separation method = solubility of the component in the liquid stationary phase

Question 8

retention time

Answer 8

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

Question 9

what determines retention time?

Answer 9

components slow down as they interact with the liquid stationary phase
the more soluble the component is in the liquid stationary phase, the slower it moves through the capillary column
retention time is longer

Question 10

determining concentrations from GC

Answer 10

prepare standard solutions of the compound
obtain gas chromatograms for each
plot a calibration curve of peak area against concentration
obtain a gas chromatogram of the compound being investigated
use the calibration curve to measure the concentration of the compound

Question 11

NMR

Answer 11

involves the interaction of materials with the low-energy radio wave region of the electromagnetic spectrum

Question 12

information from C-13 NMR spectrum

Answer 12

the chemical shift value and use of
the data sheet identifies the type of C
the number of peaks shows number of C environments

Question 13

information from H-1 NMR spectrum

Answer 13

the chemical shift value identifies the types of H environment
the number of peaks shows number of H environments
the relative peak area shows number of H in each environment
the splitting pattern shows number of adjacent H
splitting pattern = n + 1
where n = number of adjacent H

Question 14

identifying exchangeable protons (-OH and -NH protons)

Answer 14

protons attached to -OH, -COOH and -NH2 can exchange with the protons in water
run a H-1 NMR spectrum on the compound
add D2O to another sample
run a second H-1 NMR spectrum on the sample
any peak due to -OH or -COOH or -NH disappears