Understanding Discord NSFW Servers A Guide for Responsible Users.pdf
Chapter 24 gc
1. Gas Chromatography
Mobile phase: Gas (H2, He, N2)
Stationary phase: Nonvolatile liquid or solid
Solute: gas or volatile liquid
GC considerations: analyte must be volatile and thermally stable
Factors that influence separation
Carrier gas type and velocity
Column temperature
Column length
Column diameter
Film thickness
Stationary phase type
3. Gas Chromatography
1. Carrier Gas
• Inert
• Hydrogen, helium, nitrogen
• Often dictated by detector
2. Sample Injection System
•Temp. very important
•Avoid band broadening
•Suitable size (µL)
•Liquid/Gas: syringes
4.
5. Gas Chromatography
3. Columns
A. Packed
B. Open Tubular
A. Packed
Stainless steel or glass
3-8 mm dia
1-5 m in length
Fine solid support coated with nonvolatile liq
Strong solid support
6. Gas Chromatography
B. Open Tubular
Fused silica with
nonvolatile liquid
coated on it
Advantages
Higher Rs
Shorter time
Less sample
9. Gas Chromatography
A. Solid Support
Small uniform particles
Good mechanical strength
High surface area
Inert at high temperature
Usually 150 – 250 µm dia
10. B. Stationary Phase: Volatile liquid
Low volatility
Good thermal stability
Chemical inertness
“appreciable” solvent power
“like dissolves like”
18. Gas Chromatography
4. Detector
– Sensitive
– Stable
– Linear
– Versatile
– Response time
– Selective
Most Common
A. Thermal conductivity
B. Flame Ionization
C. Electron capture
19. Gas Chromatography
A. Thermal conductivity
– Simple
– Universal
– Change in thermal
conductivity of a gas
when an analyte is
present
– He, H2 have high TC
Properties
4-5 order of magn linear response
Simple
Responds to all analytes
Low sensitivity relative to others
20. Temp f(TC)
R f(Temp)
Analyte dec TC,
inc Temp, inc R
TC detector
21. Gas Chromatography
B. Flame Ionization
– Burn elutate in a mixture of H2 and air – create
ions and electrons
– Response prop. to solute mass
– Insensitive to H2, He, N2, CO2, NH3, carbonyl…
Properties
High sensitivity
Large linear response 107
Destructive
Good detection limits
23. Gas Chromatography
C. Electron Capture
– Ionize gas entering detector with high energy
electrons
– Measure current
– Analyte that has affinity for e-, captures them
Properties
Sensitive to halogens, conj. Carbonyls, nitriles, nitro compds
Selective
Small linear range, 102
Non-destructive