GC-FID
Definition
Gas chromatography with flame ionisation detection. The standard analytical method for quantifying cyanide and methanol in blood and tissue specimens. Provides both identification and quantification in a single analytical run.
- Full name
- Gas chromatography with flame ionisation detection
- Primary forensic use
- Quantifying cyanide and methanol in blood and tissue
- Output
- Both identification and quantification in one run
Common questions
Why is GC-FID favoured for cyanide and methanol quantification specifically?+
Both compounds are small, volatile molecules that separate cleanly on GC and produce a strong, reproducible flame ionisation signal proportional to carbon content, giving reliable quantification without needing the added complexity of mass spectral confirmation for these well-characterised analytes.
How does GC-FID differ from GC-MS in what it can tell an examiner?+
FID detects and quantifies compounds by a universal carbon-based signal but does not confirm molecular identity the way mass spectral fragmentation does, so GC-FID results for an unexpected or contested compound are often backed up with GC-MS confirmation, while routine known analytes like methanol are commonly reported from FID alone.
What sample preparation issue matters most for GC-FID cyanide analysis?+
Cyanide is volatile and can be lost or artificially generated during storage and handling, so samples are typically preserved and analysed promptly using headspace or distillation methods before GC-FID injection to avoid under- or overestimating the true blood concentration.
Related terms
- Bitter-Almond Odour
- The characteristic smell of hydrogen cyanide, detectable at autopsy in approximately 40% of people (a genetically determined anosmia to HCN). Present in...
- Carboxyhaemoglobin (COHb)
- The compound formed when carbon monoxide binds to haemoglobin at the oxygen-binding site, with an affinity 200-250 times greater than oxygen. Produces...
- Cherry-Red Livor Mortis
- Bright pink-red post-mortem lividity produced by the spectral absorption shift of carboxyhaemoglobin; also seen in cyanide poisoning and hypothermia. Distinguished from natural...
- Co-Oximetry
- Spectrophotometric analysis of blood that simultaneously quantifies oxyhaemoglobin, deoxyhaemoglobin, carboxyhaemoglobin, methaemoglobin, sulphhaemoglobin, and total haemoglobin by their distinct absorption wavelengths. The primary...
- Cytochrome C Oxidase (Complex IV)
- The terminal electron acceptor in the mitochondrial respiratory chain, inhibited by both cyanide and hydrogen sulphide. Inhibition prevents oxidative phosphorylation and ATP...
- Knockdown Pattern (H2S)
- The scene distribution of multiple H2S victims clustered at the entrance or access point of a confined space, as first responders and...
- Sulphhaemoglobin (SHb)
- A modified haemoglobin species in which one or more pyrrole rings is sulphonated by reaction with hydrogen sulphide. Produces green-brown blood and...