Ethanol was purchased from Romil, while ultra-pure water
from a Milli-Q system (Millipore, Bedford, MA) with a conductivity
of 18 MΩ was used throughout. Sodium sulfate (Na2SO4) and 2-
octanone were from Sigma-Aldrich (St Louis, MO). Helium at a purity
of 99.999% (Rivoira, Milan) was utilised as the GC carrier gas.
The SPME fibres and glass vials were from Supelco (Bellefonte,
PA). The SPME fibres were conditioned as recommended by the
manufacturer, but below the maximum recommended temperature
prior to their first use. Before the initially daily analysis, the
fibres were conditioned for 5 min at the operating temperature
of the GC injector port and the blank level was checked. Duplicate
analyses were performed.