Final Review

Question 1

Distribution coefficient

Answer 1

K = Cs / Cm = k’(Vm / Vs)

Question 2

Adjusted (relative) retention time and retention volume

Answer 2

t’r = tr - tm
V’r = Vr - Vm

Question 3

Asymmetry factor As > 1

Answer 3

Tailing

Question 4

Asymmetry factor As < 1

Answer 4

Fronting

Question 5

Draw GC setup

Answer 5

Question 6

Diffusion coefficients of carrier gases

Answer 6

H2 > He > N2

Question 7

Carrier gas efficiency (plate height) at twice Uopt

Answer 7

He and H2 acceptable > N2 bad

Question 8

When to choose splitless mode injector?

Answer 8

Low analyte concentration < 50 ng
0.5-1 uL injection
No degradation of analytes with T
Not a wide bp range

Question 9

When to choose split mode injector?

Answer 9

High analyte concentration > 50 ng
0.5-1 uL injection
No degradation of analytes with T
Not a wide bp range

Question 10

When to choose PTV injector?

Answer 10

Wide concentration range
Normal to large injection volume
WIDE BP RANGE

Question 11

When to choose cold-on-column injector?

Answer 11

Low bp analytes
Analytes that elute near solvent front

Question 12

When to choose thermal conductivity detector (TCD)?

Answer 12

Valuable analyte (non-destructive)
Using He or H2 gas (large difference in thermal conductance)
Have difficult to detect analytes (universal)

Not good for trace analysis

Question 13

When to flame ionization detector (FID)?

Answer 13

Carbon containing/organics (universal)
Higher sensitivity

Question 14

When to choose nitrogen phosphorus detector (NPD)?

Answer 14

Nitrogen and phosphorus containing compounds

Question 15

When to choose flame photometric detector (FPD)?

Answer 15

Phosphorus and sulfur containing compounds

Question 16

When to choose electron capture detector (ECD)?

Answer 16

Halogenated and nitro compounds, high sensitivity for electrophilic species (atoms with high electron affinity)

Question 17

Draw TCD

Answer 17

Question 18

Draw FID

Answer 18

Question 19

Draw NPD

Answer 19

Question 20

Draw FPD

Answer 20

Question 21

Draw ECD

Answer 21

Question 22

van Deemter equation and proportionality of each term

Answer 22

H = A + B/u + Cu

A ~ packing factor (λ) and particle size (dp)
B ~ obstruction factor (γ) and diffusion coefficient (Dm)
Cm ~ dp^2 / Dm

Question 23

Draw HPLC setup (gradient elution)

Answer 23

Question 24

When to choose UV-vis detector?

Answer 24

Functional groups, and electron withdrawing groups (halogens, NO2, COOR)

Question 25

When to choose Fluorescence detector?

Answer 25

Functional groups, and electron donating groups (NH2, R, OH, OR), rigid aromatic groups, conjugated

Question 26

When to choose refractive index detector?

Answer 26

Alkanes present (not a chromophore or fluorophore)