Headspace GC
Definition
Gas chromatography in which the sample (blood, urine, vitreous) is sealed in a vial, equilibrated at a fixed temperature, and a portion of the vapour above the liquid is injected. The method of choice for ethanol, methanol and volatile cyanide.
- Primary compounds detected
- Ethanol, methanol, and volatile cyanide
- Sample types
- Blood, urine, and vitreous samples
- Standard in Indian labs
- Routine method at forensic science labs for ethanol analysis and fire-debris work
Common questions
What is headspace GC used for in forensics?+
It's a gas chromatography method that detects volatile poisons and gases in biological samples like blood and urine. The sample is sealed in a vial, heated to release vapors above the liquid, and those vapors are then injected into the instrument for analysis. It's the standard technique for detecting ethanol, methanol, and cyanide in forensic laboratories.
How does headspace GC work differently from regular chromatography?+
Instead of analyzing the entire sample, headspace GC only samples the vapors above a heated, sealed liquid. This leaves the solid and liquid matrix behind, making it simpler and faster. It's especially good for volatile compounds that naturally want to evaporate.
Where is headspace GC commonly used in forensic labs?+
It's the standard method at forensic science labs across India for analyzing blood ethanol levels, detecting volatile poisons, and examining fire debris.
Related terms
- Anion Gap
- Sodium minus the sum of chloride and bicarbonate in serum. A widened anion gap (above 16) in a comatose patient with unexplained...
- Capillary Column
- A fused silica tube 15 to 60 m long with an internal diameter of 0.25 to 0.53 mm and a stationary liquid...
- 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...
- Carrier Gas
- The inert mobile phase that sweeps the sample through the column. Helium is traditional and gives the best peak shape on capillary...
- Cherry-Pink Lividity
- The bright pink discolouration of dependent tissues seen in CO and cyanide deaths. In CO the colour comes from COHb itself, in...
- Conway Microdiffusion
- A two-chamber glass cell in which an acid in the outer ring liberates HCN from the sample and the gas diffuses into...
- Derivatisation
- A pre-injection chemical step that converts polar, non-volatile or thermally fragile analytes into volatile, GC-friendly derivatives. Silylation with BSTFA is the most...
- ECD
- Electron capture detector. A Ni-63 radioactive source produces a baseline electron current that is reduced when electron-affinic species (halogens, nitro groups, peroxides)...
- FID
- Flame ionisation detector. A hydrogen-air flame ionises C-H bond containing analytes and a collector electrode reads the ion current. Near-universal for organic...
- Saturation Kinetics
- Enzyme behaviour at substrate concentrations above the Km, where the rate of metabolism is constant rather than proportional to concentration. Ethanol saturates...
Explained in these topics
- Gas-Liquid Chromatography (GLC): Columns, Carriers and DetectorsA sample preparation mode where the vapour above a heated, sealed sample vial is sampled and injected, leaving the matrix behind. Standard at every Indian SFSL...
- Gases and Volatile Poisons: CO, Cyanide, Methanol, EthanolGas chromatography in which the sample (blood, urine, vitreous) is sealed in a vial, equilibrated at a fixed temperature, and a portion of the vapour above the...