Final Review Flashcards
Distribution coefficient
K = Cs / Cm = k’(Vm / Vs)
Adjusted (relative) retention time and retention volume
t’r = tr - tm
V’r = Vr - Vm
Asymmetry factor As > 1
Tailing
Asymmetry factor As < 1
Fronting
Draw GC setup
Diffusion coefficients of carrier gases
H2 > He > N2
Carrier gas efficiency (plate height) at twice Uopt
He and H2 acceptable > N2 bad
When to choose splitless mode injector?
Low analyte concentration < 50 ng
0.5-1 uL injection
No degradation of analytes with T
Not a wide bp range
When to choose split mode injector?
High analyte concentration > 50 ng
0.5-1 uL injection
No degradation of analytes with T
Not a wide bp range
When to choose PTV injector?
Wide concentration range
Normal to large injection volume
WIDE BP RANGE
When to choose cold-on-column injector?
Low bp analytes
Analytes that elute near solvent front
When to choose thermal conductivity detector (TCD)?
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
When to flame ionization detector (FID)?
Carbon containing/organics (universal)
Higher sensitivity
When to choose nitrogen phosphorus detector (NPD)?
Nitrogen and phosphorus containing compounds
When to choose flame photometric detector (FPD)?
Phosphorus and sulfur containing compounds
When to choose electron capture detector (ECD)?
Halogenated and nitro compounds, high sensitivity for electrophilic species (atoms with high electron affinity)
Draw TCD
Draw FID
Draw NPD
Draw FPD
Draw ECD
van Deemter equation and proportionality of each term
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
Draw HPLC setup (gradient elution)
When to choose UV-vis detector?
Functional groups, and electron withdrawing groups (halogens, NO2, COOR)
When to choose Fluorescence detector?
Functional groups, and electron donating groups (NH2, R, OH, OR), rigid aromatic groups, conjugated
When to choose refractive index detector?
Alkanes present (not a chromophore or fluorophore)
