1. Gas Chromatography Chap 27 Types: Gas-solid chromatography (GSC)
Limited application
Gas-liquid chromatography (GLC)
Widely used and called “GC”

2. Schematic of a Gas Chromatograph
Fig. 27-1
He, N2, or H2
T = room + 10°  400°C

3. Effect of mobile-phase flow rate on plate height
A van Deemter Plot:
Effect of mobile-phase flow rate on plate height
Analogous to Fig

4. Injection Port for Split Injection into
an Open Tubular Column
Analogous to Fig. 27-3
~ 50 °C > column oven
∼0.001 μL
∼0.1 μL

5. Injector System For samples that decompose above BP and for Quant
Routine for small
sample volume into
OT capillary column
Best for trace levels
of analytes < 0.01%

6. Comparison of 1% methyl isobutyl ketone (BP 118 °C)
and 1% p-xylene (BP 138 °C) in CH2Cl2 (BP 40 °C)
(splitless)

7. GC Columns Two types: Packed (for large samples sizes)
Al, Cu, SS, or glass
packed with diatomaceous earth or Chromosorb®
Open Tubular (capillary)
commonly of fused silica (FSOT)
coated with polyimides  flexible, non-wetting
greater speed and higher N than packed columns

8. Open Tubular Columns
Capillary Columns

9. Typical Fused Silica Open Tubular Column
(FSOT)
L = 20 – 100 m
id = 0.1 – 0.53 mm
N = 2 x 104 – 4 x 105

10. Stationary Phase Characteristics of immobilized liquid phase:
low volatility (BP > oven °C)
thermal stability
chemical stability
solvent characteristics (polar or nonpolar)
Most are poly hydrocarbon siloxanes:

11. Table 27-3

13. Table 27-2

14. Chromatogram of Vapors From the Headspace of a Can of Beer
FSOT column
0.25 mm x 30 m
20% Carbowax
30 °C for 2 min
Ramped to 160 °
at 20 °/min
FID detector

15. Common Detectors for GC
Flame ionization detector (FID)
Thermal conductivity detector (TCD)
Electron capture detector (ECD)
Photoionization detector (PID)

16. Flame Ionization Detector (FID)
Fig 27-8
Most widely used
Mass-sensitive
High sensitivity (∼10-13 g)
Large linear range
Low noise
Destructive of sample

17. Thermal Conductivity Detector (TCD)
Fig. 27-9(a)
Simple, classic design
Concentration sensitive
Measures change in
conductivity of He when
analyte is present
Large linear range
Relatively poor sensitivity
∴ can’t be used with
capillary columns
Nondestructive of sample

18. Thermal Conductivity Detector (TCD)
Fig. 27-9(b)

20. Electron Capture Detector (ECD)
Fig
From column N2
To exhaust
Radioactive
β-emitter: Ni-63 + −
Concentration sensitive
Highly selective to molecules containing electronegative groups:
halogens, (especially insecticides) peroxides, nitro groups, etc.

21. Photoionization Detector (PID)
10 – 12 eV
Highly sensitive to aromatics & organo-sulfur & -phosphorous

23. Purge and Trap Method Extraction of a volatile analyte
from a liquid matrix
Uses He to purge or “sparge”
analyte from matrix
e.g., drinking water treatment
includes chlorination but
Cl2 reacts with organics to
produce nasty THMs
trap
purge