GC Detectors
Ideal Detector Characteristics:
1. Universal Response
2. High Sensitivity
3. Reproducible
4. Large linear Dynamic Range
5. Fast Response Time
6. Non-Destructive

GC Detectors
Ideal Detector Characteristics:
1. Univeral Response
2. High Sensitivity
3. Reproducible
4. Large linear Dynamic Range
5. Fast Response Time
6. Non-Destructive

Thermal Conductivity Detector
(TCD)
Thin wire resistively heated in a flowing stream of thermally conductive gas.
When analyte present, gas is less efficient at cooling the wire.
The wire therefore increases in temperature, and it’s resistance changes.

Thermal Conductivity Detector
(TCD)
Typically employ 2 resistors: one in analyte stream and one in reference stream. A circuit measures the difference in resistance between the two filaments.

Flame Ionization Detector (FID)
Carbon-containing analytes are oxidized to ionic species in a hydrogenoxygen flame. A current is measured between 2 electrodes placed in the flame.

Nitrogen Phosphorous Detector (NPD)
Nitrogen-containing or Phosphorus-containing species elute into a cool flame
(excess H
2
). A heated Rb bead interacts with N or P to produce ions that are then collected as a current between electrodes. Like the FID, the NPD is a
Thermionic Detector .

Electron Capture Detector (ECD)
A radioactive foil ( 63 Ni) constantly ionizes the carrier gas effluent producing a constant current between two electrodes.
Highly electronegative, or polarizable analyte molecules take up some of the electrons as they pass by. These molecules are much less mobile than the free electrons, and thus are less likely to get to the collector electrode.
Signal varies greatly with polarizability (big floppy electron
“sponges” give highest signal.

Atomic Emission Detector (AED)
Usually a Microwave Induced Plasma (MIP)

Infrared Absorption Detector (GC-IR)
Provides gas phase IR spectrum of each peak (qualitative analysis).
Spectrum collection must be quick (FTIR).
Pathlength is optimized with a light pipe.

Mass Spectrometry Detector (GC-MS)
Provides mass spectrum of each peak (qualitative analysis).
Mobile phase stream must be transported to a vacuum.
View Chromatogram at a single mass, or view MS spectrum for
Each peak.