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Gas Chromatographic Detectors

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    Learning Objectives

    All students are expected to:

    • Evaluate the suitability of three common detectors (FID, TCD, and ECD) for different analytes
    • Explain the operation principle of these detectors
    • Differentiate these detectors in terms of selectivity and other properties (destructive, bulk, concentration/ mass depending) with regard to their suitability for different application

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    Quiz  GC Detectors

    Provide handwritten answers and bring them to the class

    1. Define the limit of detection, dynamic range, linear range and also significance of these parameters when selecting a detector

     

     

    1. Describe how FID works, provide its significant characteristics and optimization parameters

     

     

     

    1. Describe how ECD works, and describe its typical operation parameters

     

     

     

    1. Describe how TCD works, and describe its typical operation parameters

     

     

     

     

    1. Define the main classifications of common chromatographic detectors and give examples in terms of:
      • Concentration vs. mass flow
      • Selective vs. universal
      • Destructive vs. nondestructive

     

     

     

     

     

    A.  Flame Ionization detector  (FID)

    1. Fill the missing labels for the FID detector diagram below.

      Diagram_FID_Detector.png

     

    1. Explain the purpose of using each gas.

     

     

     

     

    1. Explain the operational principle of FID.

     

    1. Which analytes can be analyzed on an FID and which cannot?

     

     

    B.  Thermal conductivity  detector (TCD)

    1. Sketch the flow of the molecules in a single cell TCD for the 2 scenarios shown below
      1. a reference gas passing through the filament
      2. an analyte in a carrier gas passing through the filament

      TCD.png

    1. Why is a valve switching required for the application shown below?

      Application.pngThermalConductivities.png

      Hint: Consider thermal conductivities listed.

     

    C.  Electron Capture  detector (ECD)

    1. Sketch fast β- and thermal electrons e-, makeup gas and carrier gases, analyte species CX in the following three scenarios for ECD
      1. Only the carrier gas is passing through the ECD
      2. Both carrier and makeup gases are passing through the ECD
      3. The carrier gas with an analyte and makeup gas are passing through the ECD

     

    a)

    ECD.png

    b)

    ECD.png

    c)

    ECD.png

     

    1. Write three reactions, which occur in an ECD.

       

       

       

       

       

       

       

    1. Which analytes can be analyzed using an ECD?

       

       

       

       

       

    D.  GC detector characteristics

    1. List all possible detectors for the analytes in the following samples:
      • Total petroleum hydrocarbons (TPH) in gasoline

       

      • Nitrated polycyclic aromatic hydrocarbons (N-PAHs) extracted from air particulate matter

       

      • Alcohol content in wine

       

      • Chlorinated disinfectant products in water

       

      • Polychlorinated biphenyls (PCBs) extracted from soil

       

      • Hydrogen, CO2, methane, ethane and propane from biofuel production

       

     

    1. Considering their sensitivity, highlight the detector of choice for the analytes listed above in those samples.

     

    1. What solvents used for extraction would be detrimental to the detectors proposed in response to Q2?

     

     

    1. Which detector is universal and would be suitable for all analytes and why is it not the detector of choice?

     

    1. For which application would it be suitable to use two detectors in series and what would be the benefits of such a setup?

     

     

     

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