2100:1 Partition Ratio
Definition
The conventional blood/breath partition assumption used by breath alcohol analysers worldwide: 2100 mL of venous blood contains the same mass of ethanol as 1 mL of alveolar air at body temperature. Population mean, with individual variation from approximately 1700:1 to 2400:1.
- Assumption
- 2100 mL venous blood ≈ ethanol in 1 mL alveolar air
- Type
- Population mean partition coefficient
- Individual range
- Approximately 1700:1 to 2400:1
- Used by
- Breath alcohol analysers worldwide
Common questions
Why does individual variation in this ratio matter for a breath test result?+
Because analysers assume a fixed 2100:1 ratio, a person whose true physiological ratio is lower, closer to 1700:1, will have their breath reading overestimate their actual blood alcohol concentration, which can matter in a contested case.
How is the ratio actually used to produce a blood alcohol equivalent from a breath reading?+
The ethanol mass measured per litre of breath is multiplied by 2100 to estimate the equivalent ethanol concentration per litre of blood, the standard conversion built into evidential breath testing instruments.
Related terms
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- 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)
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- 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...
- Static Headspace
- A sample preparation technique in which a sealed vial is heated until volatile analytes reach thermodynamic equilibrium between the liquid matrix and...
- 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...