Determination of thymol and carvacrol in plasma and milk of dairy cows using solid-phase microextraction

A method for determination of thymol and carvacrol in milk and plasma of dairy cows was developed by gas chromatography-mass spectrometry (GC-MS) and headspace solid-phase microextraction (HS-SPME). The limits of quantification were set at 0.5 and 2.0 ng mL(-1) for both analytes in plasma and milk, respectively, with appropriate precision and accuracy. For quantification of thymol, the results obtained with the established methodology were superior compared with others reported in the literature, achieving lower limit of quantification. Concerning to carvacrol, this is the first methodology described in the literature for the analysis of this compound in plasma and milk of cows. The analytical methodology enabled the identification and quantification of thymol and carvacrol in the plasma and milk of cows after administration of an intra-mammary phytoformulation of veterinary use containing plant essential oils rich in thymol and carvacrol.