Flame Ionization Detection (FID)

The FID is the detector used on the Shimadzu GC-2025. It is the most commonly used reference detector in gas chromatography.

Detection Mechanism

When compounds elute from the column, they enter the FID where a combustion-based process generates a measurable signal:

Gas mixing — column outlet gas mixes with hydrogen
Combustion — the mixture burns in an air atmosphere
Ionization — organic compounds combust in the flame, producing ions via the reaction:
```
CH + O → CHO⁺ + e⁻
```
Signal generation — a DC voltage between the flame jet and a collector electrode draws ions to the collector, producing a small current that is amplified into the chromatographic signal

📋 From course materials + 221-79103D_GC-2025_IM_EN.pdf

📋 From manual

Nearly universal for organic molecules — almost all carbon-containing compounds burn and yield ions
High sensitivity — minimum detection of 2 pgC/s on the GC-2025
Wide dynamic range — 10⁷ linear range
Low dead volume
For isomers, signal is roughly proportional to the number of carbon atoms

📋 From course materials + From manual

The FID is not truly universal. Certain compound types produce weak or no signal:

Limitation	Detail
Carbonyl carbons (C=O)	Do not generate signal
Halogenated compounds	Reduced ion yield
Water (H₂O)	No signal at all
Destructive	Sample is consumed during detection

📋 From course materials

Detector	Strengths	Limitations
TCD (Thermal Conductivity)	Completely universal, non-destructive	Lower sensitivity than FID
NPD (Nitrogen-Phosphorus)	Highly sensitive/specific for N and P	Limited to N/P compounds only
ECD (Electron Capture)	Highly selective for electronegative compounds	Limited compound classes
MS (Mass Spectrometry)	Structural identification, resolves co-eluting peaks	More expensive, requires more maintenance

For GC-MS capabilities at UFAZ, see Overview (page to be created).

📋 From course materials