Optimisation of headspace solid-phase microextraction for quantitative analysis of monoterpenes in caprine blood

In order to follow the metabolic fate of α-pinene, β-pinene, p-cymene and linalool, four monoterpenes characteristic of the spring diet of dairy goats in the Basilicata region (Southern Italy), we have investigated the use of headspace solid-phase microextraction (HS-SPME) on a 100 μm polydimethylsiloxane coated fibre as a preparation technique for their analysis by gas chromatography in blood. The effects on terpenes recovery yields of exposure temperature, between 25 and 45 °C, exposure time, between 5 and 25 min, and sample ionic strength, between 0 and 250 g/L NaCl, were modelled by second order polynomials parameterised with data from a Hoke experimental design of 13 runs. HS-SPME of α- and β-pinene was mostly favoured by low temperatures and, to a lesser extent, by short extraction times in a linear way. The model fitted to p-cymene data was characterised by a curvilinear effect of extraction time (main effect, P = 0.04; quadratic effect, P = 0.10) and quadratic effect of salting (P = 0.04) generating a saddle-shaped surface response. Peak areas of p-cymene were lowered by intermediate NaCl concentrations and short extraction times. For linalool, all the main effects (P<0.04) and the quadratic effect of extraction time (P = 0.02) generated a hill-shaped response surface. The largest linalool peaks resulted from relatively low extraction times and high temperatures. The best set of operative conditions was an exposure temperature of 35 °C, an exposure time of 22 min and a NaCl concentration of 250 g/L. With limonene as an internal standard, the linearity, intra-assay precision and quantification limits were estimated for each terpene determination. The proposed HS-SPME method allowed fast, simple and sensitive determination of terpenes in goat blood samples by conventional equipment.