The quantitative GC analysis were carried out on a Shimadzu GC17A system equipped with a split/splitless injector and with a FID detector (Shimadzu, Japan) at the following conditions: fused-silica capillary column SE52 (Mega, Legnano, Italy) coated with (poly-5% diphenyl-95%-dimethyl-siloxane bonded phase column (30 m x 0.25 mm i.d.; 0.25 μm film thichness);