Gas Chromatography Detector (Type of GC Detectors)

Gas Chromatography Detector

Below lists are the GC Detector types

  1. Flame ionization Detector(FID)
  2. Thermal conductivity Detector(TCD)
  3. Electron Capture Detector (ECD)
  4. Flame Thermionic Detector (FTD)
  5. Nitrogen-phosphorus Detector
  6. Flame photometric Detector (FPD)
  7. Photo-ionization Detector (PID)
  8. Electrolytic Conductivity Detector (ELCD)
  9. Barrier Discharge Ionization Detector (BID)
  10. Sulfur chemiluminescence Detector (SCD)
  11. Gas chromatography–mass spectrometry (GC-MS) 

Related: Gas Chromatography Columns, Principle of HPLC

Type and Details of Gas chromatography Detectors

1. Flame Ionization Detectors (FID) :

  • In gas chromatography, the FID is the most popular detector.
  • The Flame Ionization Detectors (FID) is sensitive to, and capable of detecting, substance that contain carbon atoms (C), which make up nearly all organic substances.
  • Carbon atoms having a double bond to oxygen, such as those found in carbonyl and carboxyl groups (CO, CO2, HCHO, HCOOH, CS2, CCl4, etc.) are not sensitive to the FID.
  • Working Principle:
    • Analyst substances are burned in a hydrogen-air flame.
    • The hydrogen flame oxidizes the carbon in a sample carried into the FID detector on carrier gas, causing an ionization reaction.
    • A collector electrode attracts the generated ions to an electric field. A signal is generated by counting the number of ions that hit the collector.
Flame Ionization Detectors (FID)
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2. Thermal Conductivity Detector (TCD)

  • Mechanism:
    • A detector cell contains a heated filament with an applied current.
    • As carrier gas-containing solutes pass through the cell, a change in the filament current occurs.
    • A heated filament with an applied current is contained within a detection cell. The filament current changes as a carrier gas containing solutes travels through the cell.
    • The current change is compared to a reference cell’s current. A signal is generated after the difference is measured.
Thermal Conductivity Detector (TCD)
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3. Electron Capture Detectors (ECD)

  • For electrophilic substances, the Electron Capture Detector (ECD) is a selective, high-sensitivity detector. The ECD can detect organic halogen substances, organic metal compounds, diketone compounds, and other organic molecules.
  • Mechanism:
    • A 63Ni foil lining the detector cell provides electrons. In the cell, a current is generated.
    • The current is reduced when electronegative substances collect electrons. A signal is generated once the quantity of current loss is indirectly assessed.
Electron Capture Detectors (ECD)

4. Flame Thermionic Detector (FTD)

  • It is ideal for organic nitrogen compounds and inorganic and organic phosphorus compounds
  • Mechanism:
    • The FTD reads the change in ion current obtained at the collector to detect ions.
    • When a current is supplied through a platinum coil with an alkali source (rubidium salt) attached, the coil heats up, causing plasma to form around the alkali source.
    • A current flows when ions collected in the collector.
Flame Thermionic Detector (FTD)

5. Nitrogen-Phosphorus Detector  (NPD)

  • Also know as Thermionic specific detector (TSD)
  • Mechanism:
    • Compounds are burnt in a plasma that surrounds a rubidium or cesium bead, that receives hydrogen and oxygen.
    • Compounds containing nitrogen and phosphorus produce ions that attract the collector.
    • A signal is generated by counting the number of ions that hit the collector.
Nitrogen-Phosphorus Detector  (NPD)

6. Flame Photometric Detector (FPD)

  • It is capable of detecting phosphorus (P) compounds, sulfur (S) compounds, and organic tin (Sn) compounds. The Flamephotometric (FPD) is highly selective as it detects element-specific light emitted within a hydrogen flame.
  • Mechanism:
    • A H2-O2 flame is used to burned Compounds. Sulfur (S) and phosphorous (P) containing compounds produce light-emitting species (sulfur at 394 nm and phosphorous at 526 nm).
    • A monochromatic filter allows only one of the wavelengths to pass. A photomultiplier tube is used to measure the amount of light and a signal is generated.
    • A different filter is required for each detection mode.
    • The photomultiplier tube then converts the detected light intensity into an electrical signal.
Flame Photometric Detector (FPD)

7. Photo-Ionization Detector (PID)

  • Mechanism:
    • High-energy photons emitted from a lamp bombard compounds eluting into a cell.
    • Ionization occurs in compounds with ionisation potentials lower than the photon energy. The ions are then attracted to an electrode, measured, and a signal is produced.
Photo-Ionization Detector (PID)

8. Electrolytic conductivity detector (ELCD)

  • Mechanism:
    • Compounds are combined with a reaction gas and pushed through a reaction tube at a high temperature. The reaction products are mixed with a solvent and passed through an electrolytic conductivity cell.
    • A signal is obtained by measuring the change in the solvent’s electrolytic conductivity.
    • The temperature of the reaction tube and the solvent used decide which chemicals are identified.
Electrolytic conductivity detector (ELCD)

9. Barrier Discharge Ionization Detector (BID)

  • It can detect all inorganic and organic compounds except, He and Ne.
  • Principle of detection:
    • The Barrier Discharge Ionization Detector generates a stable Helium (He) plasma, uses the energy produced by the excited Helium (He) to ionize substances, then attracts these ions to a detector’s collector.
    • The plasma energy emitted by Helium (He) is incredibly high, capable of ionizing all compounds except He, which is used to form the plasma, and Ne, which has a very high ionization energy.
    • As a result, it can detect any substances, other than He and Ne.
Barrier Discharge Ionization Detector (BID)

10. Sulfur Chemiluminescence Detector (SCD)

  • Sulfur chemiluminescence Detector (SCD) is one of Gas Chromatography Detector used for sulfur contain substance mainly.
  • Mechanism:
    • The chemiluminescence reaction generated by ozone oxidation is employed by the sulphur chemiluminescence detector (SCD).
    • Inside an extremely high temperature (about 1000 °C) oxidative-reductive furnace, sulphur compounds are transformed to an X-S chemical species (mostly SO) capable of chemiluminescence.
    • The chemical species X-S is delivered to the detector area, where it is converted to an excited-state SO2* by ozone (radical). When SO2* returns to its base state, it emits light, which the SCD detects by measuring this light with a photomultiplier tube.
Sulfur Chemiluminescence Detector (SCD)
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11. Gas chromatography–Mass Spectrometry (GC-MS)

  • GC-MS is more advanced Gas Chromatography Detector for identified the impurity.
  • Mechanism:
    • The detector is kept under vacuum. Analysts (Sample) are bombarded with electrons (EI) or gas molecules (CI). Charged ions or fragments are formed when compounds fragment.
    • These ions are focused and accelerated into a mass filter. The mass filter selectively permits all ions of a precise mass to pass through to the electron multiplier.
    • All ions with a particular mass are identified. The mass filter then lets the next mass through while rejecting all others.
    • Several times per second, the mass filter scans progressively through the defined range of masses.
    • For each scan, the total number of ions is counted. The chromatogram is created by plotting the number of ions per scan against time. For each scan, a mass spectrum is generated, which shows the various ion masses against their abundance or number.
    • Selectivity refers to a compound’s ability to produce fragments within a given mass range. May be an inclusive range of masses (full scan) or only select ions (SIM)
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