Flame ionization detectors (FID) in total hydrocarbon gas analysis

In the field of total hydrocarbon gas analysis, flame ionisation detectors (FIDs) are reliable, proven and extremely robust measuring instruments. They are used wherever hydrocarbon compounds in the air need to be monitored or measured, whether in industrial environments, for emissions monitoring, or as part of statutory environmental monitoring.

The way an FID works is based on the ionisation of organic compounds in a flame. To achieve this, a continuously aspirated gas sample is fed to the detector via a heated sampling line. This line is heated to prevent condensation and ensure the integrity of the gas sample. Inside the detector, the sample gas enters a hydrogen diffusion flame. This burns at a defined ratio of hydrogen and air or another carrier gas.

When hydrocarbons enter the flame with the gas flow, they are thermally decomposed by the high energy input. This produces CH radicals, which then react with oxygen atoms to form CHO ions. These ionised fragments are stripped from the flame by an electric field, resulting in a measurable current. The intensity of this current is directly proportional to the concentration of hydrocarbons in the gas.

FID systems are ideal for continuously monitoring exhaust air flows in industrial plants, particularly when used with exhaust air purification systems in accordance with the requirements of the Federal Immission Control Act (BImSchG). Thanks to their high level of accuracy, fast response times and insensitivity to inert gases, they are the preferred measurement system for many plant operators and testing institutes.

Mobile FID devices are widely used by technical inspection associations (TÜV) and accredited environmental measurement bodies. They are also useful for internal applications, such as process analysis and control. They enable precise control of production processes, particularly those involving volatile organic compounds (VOCs).

Inline FIDs are particularly advantageous for measuring the lower explosion limit (LEL). They are integrated directly into the process and offer an extremely fast response time — a decisive advantage in safety-critical applications. Thanks to their robust design and long service life, these robust devices also perform well in environments with high levels of dust or condensation.

Due to their versatility and high reliability, flame ionisation detectors have become indispensable in numerous industrial, safety-related, and environmentally relevant applications.