The photoionization detector (PID) operates on the principle of ionizing gas and vapor molecules using high-energy ultraviolet (UV) radiation. Here is a detailed description of the operation of the PID:
The device is equipped with a vacuum ultraviolet (VUV) light source (VUV lamp), which emits photons with an energy of about 10 eV, sufficient to ionize many organic compounds but insufficient to ionize air molecules (oxygen, nitrogen, carbon dioxide, etc.).
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The gas or gas mixture to be analyzed enters the ionization chamber through a filter membrane. VUV lamp photons enter the ionization chamber, where molecules with an ionization energy lower than the photon energy are ionized, producing positive ions and electrons. how does photoionization detector work
There are several electrodes in the chamber (cathode, anode, and grid electrode). The electrodes create an electric field that separates the generated ions and electrons. The separated charges move toward the electrodes, generating a measurable electric current. The magnitude of this current is proportional to the concentration of the ionizable substance in the analyzed gas. A special grid electrode reduces the influence of moisture and other contaminants on the readings.
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The signal is amplified and converted into a numerical value of the substance concentration, which is displayed on the instrument. What types of gases can photoionization detectors measure
The main advantages of FID are high sensitivity to volatile organic compounds, the ability to measure low concentrations, resistance to the effects of aggressive components, and insensitivity to the main components of air. FID is widely used in gas analyzers and gas chromatography for monitoring pollutants and toxic substances. What is a PhotoIonization Detector used for?
Thus, a FID is an accurate and reliable instrument for measuring the concentrations of organic and some inorganic gases in the air using the process of photoionization under UV radiation exposure.
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