Gas chromatography

Reducing plate height

Decrease column radius

Decrease stationary phase thickness

Increase temperature

Columns

1) WCOT

2) PLOT

3) packed - poor resolution, large sample capacity

Smaller diameter, better resolution

Nonpolar stationary phase

Nonpolar elute according to BP

polar not retained

Polar stationary phase

Elute based on polarity and BP

Types of separation

1) isothermal

2) programmed temp

Carrier gas

H2 and He, better resolution than N2 at high flow rate

Solvent trapping

Initial temp 10-20 below BP

Solvent condenses

Solutes trapped before separation

>30° above BP

Injectors

1) on column

2) direct

3) loop

TCD

Measures ability of analyte to transport heat

Analyte mixed with carrier gas lowers its thermal conductivity

Poor sensitivity

Non destructive

Responds to concentration

FID

Measures electric current

Broadest linear dynamic range

Hydrogen air flame

High sensitivity for hydrocarbons

ECD

Electrons from radioactive source produce thermal electrons

Analyte captures the electrons, reduces the standing current

High sensitivity for electronophillc groups such as halogens nitriles and nitro groups

Non destructive

Responds to concentration

Photoionization detector

Uv light ionizes

For aromatics

Nondestructive

FPD

Measures emission of excited atoms in flame

For sulphurs and phosphorus

TID/NPD

Rb salt above flame

For nitrogen and phosphorus

Sulphur chemiluminescence detector

Measures emission from excited SO2 caused by oxidation of sulphur

High sensitivity for sulphur

Nitrogen chemiluminescence detector

Measures emission from excited NO2 caused by oxidation of nitrogen

High sensitivity for nitrogen

AED

Measures emission of atoms in microwave plasma

Element selective

FTIR

Measures IR absorption in the gas phase

Low sensitivity

Mass spectrometric detector

Most powerful

High resolution

Based on mass spectra

ICP MS detector

Expensive

Powerful

Element selective

VUV

Measures absorbance of 115-185

Respond to concentration

SPME

Solvent free sample preparation

Coated fibre to extract and concentrate volatile compounds from samples

Requires calibration

GC detectors

1) TCD

2) FID

3) ECD

4) Photoionization

5) FPD

6) TID

7) Sulphur chemiluminescence

8) Nitrogen chemiluminescence

9) AED

10) FTIR

11) MS

12) ICPMS

13) VUV