Of each sample, 1 μl was analysed on a 30-m ×0.25-mm-ID crosslinkedmethyl silicone gum (HP-1) (0.25-μm-thick film) capillary gas chromatography column combined with a 5-m ×0.25-mm HP uncoated, deactivated retention gap and a 20-cm × 0.5-mm HP uncoated, deactivated retention gap as pre-column.