A flame ionization detector (FID) detects hydrocarbons in a gas sample by creating a charged current between a flame jet and an electrode. The FID is connected to a gas chromatograph to analyze the sample’s chemical composition. The FID is commonly used in pharmaceutical manufacturing and pesticide analysis but can only detect organic compounds.
A flame ionization detector (FID) is an instrument used to detect the presence of hydrocarbons, especially butane, hexane and other carbon-containing compounds that may be present in the sample being measured. The instrument is connected to a gas chromatograph via a tube called a capillary and features a chamber with a flame. Gases are injected into this chamber from one source, while hydrogen and oxygen are added from another. An electric ignition component is used to ignite the flame inside; the subsequent combustion of hydrogen and oxygen creates a charged current between the flame jet, which acts as an electrode, and another electrode in the chamber.
The capillary column inserted in the instrument is connected to the gas chromatograph, a device used to analyze the chemical composition of a gas sample. This is the tool by which the response is measured. The cylindrical electrode surrounding the flame collects the ions formed from the combustion process when a voltage is applied between the two. A current is generated and then amplified while the output is collected by electronic data collectors. Each type of gas has a specific base current and flow rate, and once traced, operators can determine the gas present by consulting a guide showing typical flow rates for different gases.
When fuel is added to a flame ionization detector, it is activated at a predetermined rate. After the air has been pumped out, the flame is lit and left for an hour to settle and burn continuously for the most accurate results. Shutting off the flow for fuel extinguishes the flame and thus the inflow for other gases is turned off. A handheld detector works in a similar way and is commonly used to monitor volatile organic compounds (VOCs). With these, the sensitivity can be adversely affected if the temperature changes rapidly or if there are strong electric fields in the environment.
A flame ionization detector can only detect organic compounds. The instrument is commonly used for pharmaceutical manufacturing and pesticide analysis. It is possible to measure methane or even toxic compounds, such as hydrogen cyanide, because they contain carbon molecules. Inorganic gases are difficult to detect with an FID. Ammonia, for example, has no carbon in its molecular structure, so it might go unnoticed.
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