Headspace GC-FID
Definition
Gas chromatography with flame-ionisation detection run on the vapour above a sealed sample. The standard forensic method for methanol and ethanol in beverages and biological fluids. On a polar wax column (DB-WAX, polyethylene glycol), methanol elutes before ethanol.
- Method
- Headspace GC-FID
- Sample types
- Blood, urine, vitreous humor, seized liquor
- Target analyte
- Ethanol
- Status
- Gold-standard quantitative method
Common questions
Why is vitreous humor sometimes preferred over blood for postmortem ethanol testing?+
Vitreous humor is more resistant to postmortem microbial fermentation and putrefaction than blood, so it is less prone to falsely elevated ethanol readings in decomposed bodies, though blood remains standard when the body is fresh.
What internal standard practice supports the quantitative accuracy of this method?+
Laboratories typically spike each sample with a known concentration of an internal standard such as n-propanol or tert-butanol before analysis, comparing its peak area to the analyte peak to correct for injection and vaporisation variability.
Related terms
- ADH Assay
- Alcohol dehydrogenase enzymatic assay. Ethanol plus NAD+ gives acetaldehyde plus NADH; NADH absorbance at 340 nm is proportional to ethanol concentration. Fast...
- BAC
- Blood Alcohol Concentration. Mass of ethanol per unit volume of whole blood. Indian legal cut-off is 30 mg per 100 mL (0.03...
- Chromotropic Acid Test
- Confirmatory colour test for formaldehyde (and hence indirectly for methanol). Chromotropic acid (4,5-dihydroxy-2,7-naphthalenedisulphonic acid) plus concentrated sulphuric acid plus formaldehyde gives an...
- Denatonium Benzoate
- Bittering agent (Bitrex), one of the bitterest known compounds, detectable by taste at the parts-per-billion level. Added at very low concentrations to...
- Denaturant
- A chemical added to industrial ethanol to make it unfit for human consumption (and therefore exempt from beverage-alcohol excise). Indian Standards list...
- Fomepizole
- 4-methylpyrazole. A competitive inhibitor of alcohol dehydrogenase used as the first-line antidote for methanol poisoning. Ethanol (oral or IV) is the older,...
- Formic Acid
- HCOOH. The toxic terminal metabolite of methanol, produced after alcohol dehydrogenase converts methanol to formaldehyde and aldehyde dehydrogenase oxidises formaldehyde to formate....
- Fuel-Cell Breath Analyser
- Electrochemical sensor: ethanol oxidises at a platinum electrode generating a current proportional to BrAC. Specific for ethanol, used in Drager Alcotest and...
- Hooch
- Illicit, unregulated country liquor. Indian regional names include haatch, desi tharra, and santhi. Typically distilled from molasses, jaggery, or fermented fruit, with...
- IR Breath Analyser
- Infrared absorption at about 3.4 micrometres (C-H stretch) or 9.5 micrometres (C-O stretch). Specific and quantitative; used in Intoxilyzer 8000 and evidential...
- Methanol
- Methyl alcohol, CH3OH. Boiling point 64.7°C. Found in wood spirit, windshield-washer fluid, and as a deliberate adulterant in illicit liquor. Toxic via...
- Putrefactive Ethanol
- Ethanol produced post-mortem by microbial fermentation of glucose, lactate and amino acids. Can give false-positive BAC; vitreous humor is the matrix of...
Explained in these topics
- Analysis of Ethyl Alcohol in Beverages, Blood and BreathGas chromatography with flame ionisation detection on the vapour above a heated sealed vial. Gold-standard quantitative method for ethanol in blood, urine, vit...
- Analysis of Methanol, Denaturants and Illicit Liquors