3.3.5. Magnetic stirring
Magnetic stirring accelerates extraction and shortens the time
needed to reach thermodynamic equilibrium between the aqueous
and the headspace phase. For headspace, stirring should be vigorous
and constant to provide excellent reproducibility. Generally, the larger
the agitation, the faster the mass transfer between the aqueous phase
and the headspace. The stirring speed range studied was 0–1000 rpm.
From the obtained results it can be stated that extraction efficiency
was poor without stirring and the detector responses (areas) were
higher for each analyte when the stirring rate increased. An optimal
stirring speed of 1000 rpm (the highest possible level) was used in the subsequent experiments to ensure the efficient extraction of all
hydrocarbons.