The samples
are placed in glass vials and closed with a septum. The injection
needle of the headspace sampler injects through the septum in
the vapor space of the sample. Via nitrogen an overpressure
is produced in the vial, which is relieved afterwards against
air-pressure into the sample loop. The filled sample loop is
injected via an injector into the gas chromatograph. The substances
covered in the vapor space are detected via flame ionization
detector or via heat conductivity detector, amplified electronically
and registered by means of a printer. The determined peak areas
are proportional to the amount of the detected substances and
therefore at constant sample loop volume is proportional to
the vapor pressure of the solvents. Generally the ratio of the
vapor pressure over the sample to the vapor pressure of the
pure solvents can be determined as reduced vapor pressure. A
typical curve of the reduced vapor pressure as a function of
the concentration of the non-volatile component is shown in
the following figure.
