Gas chromatography can be equipped with multiple detectors, each with its own expertise. FID (flame ionization detector) is one of the most widely used, especially in organic hydrocarbon analysis where it is almost a standard choice. HZGC-1212A can install up to two independent FID detectors simultaneously.

The working principle of FID

The core of FID is a tiny flame formed by a nozzle burning hydrogen gas. When organic compounds (hydrocarbons) enter the FID with the carrier gas, ionization occurs in the hydrogen flame, producing positive and negative ions. Under the action of the electric field generated by the polarized electrode (220-250V high voltage), these ions move in a directional manner and generate a weak ion current at the collection electrode.

The ion current is amplified by a microcurrent amplifier and the output signal is proportional to the mass flow rate of the organic compound. FID is extremely sensitive to organic compounds, especially those containing hydrocarbons. The detection limit of HZGC-1212A FID reaches ≤ 3 × 10 ⁻¹² g/s, with a linear range exceeding 10 ⁷ and a baseline noise of ≤ 5 × 10 ⁻¹⁴ A. It is an ideal detector for analyzing trace organic compounds.

Gas ratio of FID

FID requires three gases: carrier gas (N ₂ or He, ≥ 99.999%), hydrogen gas (H ₂, ≥ 99.99%), and air (as clean and dry as possible). The flow ratio of the three has a significant impact on the sensitivity and stability of FID. The typical ratio is: carrier gas 30mL/min, hydrogen 30mL/min, air 300mL/min (approximately 1:1:10). Flame instability when air flow is insufficient; Excessive hydrogen flow can cause peak inversion.

Ignition rules

The FID temperature must reach 130 ℃ or above to ignite and prevent water vapor from condensing inside the detector. HZGC-1212A is designed with an automatic ignition function: ignition is automatically executed when the FID temperature reaches 130 ℃, or the ignition button can be manually pressed or operated in the workstation software.

Shutdown sequence

This order must be remembered: first turn off hydrogen and air, cool down, and then turn off the carrier gas. The reason is that if the carrier gas is turned off first during the cooling process of the instrument, there will be air reflux inside the high-temperature detector, causing carbon deposition or oxidation damage inside the FID.

FID treatment of harmful samples

When analyzing samples containing toxic substances, the exhaust ports of FID and chromatographic columns must be led outdoors through pipelines to prevent indoor air pollution. This is the basic requirement of safety operating procedures.