Static Headspace
Definition
A sample preparation technique in which a sealed vial is heated until volatile analytes reach thermodynamic equilibrium between the liquid matrix and the gas above it; the gas phase (headspace) is injected into the GC column.
- Sample state
- Sealed, heated vial at equilibrium
- Injected phase
- Gas above the liquid matrix
- Principle
- Thermodynamic equilibrium between liquid and gas phases
- Common use
- Ethanol analysis by GC-headspace
Common questions
Why is static headspace preferred over direct injection for blood alcohol analysis?+
Injecting whole blood directly would contaminate and damage the GC column over repeated runs. Sampling only the equilibrated vapour above the sample keeps volatile ethanol quantifiable while leaving non-volatile blood components out of the instrument.
What can go wrong if the headspace vial has not reached full equilibrium before sampling?+
An incomplete equilibrium underrepresents the true vapour concentration of ethanol relative to the liquid, producing a falsely low reading, which is why fixed incubation time and temperature are tightly controlled in the method.
Related terms
- 2100:1 Partition Ratio
- The conventional blood/breath partition assumption used by breath alcohol analysers worldwide: 2100 mL of venous blood contains the same mass of ethanol...
- Beta Elimination Rate (Beta)
- The rate at which BAC falls during the post-absorptive phase of alcohol metabolism, expressed as mg/100 mL/hour. Population mean approximately 15 mg/100...
- Blood Alcohol Concentration (BAC)
- Mass of ethanol per unit volume of whole blood, expressed as mg per 100 mL (equivalent to mg/dL or mg%), or as...
- DB-ALC1 / DB-ALC2
- A matched pair of Agilent fused-silica GC columns used for dual-column orthogonal confirmation of blood ethanol. DB-ALC1 uses a polyethylene glycol stationary...
- Internal Standard (IS)
- A compound chemically near-identical to the analyte, often a deuterated isotopologue (d3-morphine, d5-EDDP, d5-alprazolam, pyrene-d10), spiked into every sample at a known...
- NIST SRM 1828
- A series of NIST-certified reference material aqueous ethanol standards (0.02 to 0.40 per cent w/v) used to calibrate forensic blood ethanol analytical...
- Partition Coefficient (K)
- The ratio of analyte concentration in the liquid phase to concentration in the gas phase at equilibrium. For ethanol in blood at...
- Sodium Fluoride / Potassium Oxalate (Grey-Top Tube)
- The standard blood collection tube for forensic ethanol analysis. Sodium fluoride inhibits microbial fermentation (which would produce artefactual ethanol post-collection); potassium oxalate...
- Widmark Factor (Rho / R)
- A dimensionless pharmacokinetic constant that represents the distribution of ethanol across body water. Averages approximately 0.68 for adult males and 0.55 for...