Gaschromatografic analytical method, where not, as usual, a liquid sample is directly injected. Instead of, in special glass vessel with a volume of 20 ml only a small sample (0.1 to 0.5 g/ml investigation material) is partially evaporated (below the boiling point of the components, mostly 60oC, where the steam pressure is directly proportional to the concentration of component in the investigation material). After balance setting between the liquid phase and the steam phase (within about 20 minutes, containing solid matrix up to 2 hours) an automatic injection from the vapour phase takes place. The advantage is that the sample will be separated from non-volatile matrix components (blood, etc.) and, among other things the separation column is not contaminated with the matrix.
In order to determine the blood alcohol concentration by headspace-GC usually an "internal standard" as tert. butanol (0.1 to 1% aqueous solution), 0.1 to 1 ml) is added and the ratio ethanol/tert. butanol after calibration with ethanol/water-standard solutions for accurate determination is used.
By headspace-GC, all volatile compounds could be determined at the same time, qualitatively as well as after calibration also quantitatively (alcohols, aldehydes, ketones, esters, halogenated hydrocarbons, gasoline, etc.). With the highest possible sensitivity the method is also used for the so-called "congeners analysis" from alcoholic beverages in blood in cases of claiming drinking after the relevant action.