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

In order to follow the metabolic fate of alpha-pinene, beta-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 mu m 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 degrees 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 alpha- and beta-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 degrees 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. (C) 2012 Elsevier B.V. All rights reserved.