Analysis of thymol and carvacrol in bovine plasma and milk using SPME for sample preparation
The carvacrol and thymol are phenolic monoterpenes found in essential oils, and are active in a formulation for intramammary treatment of mastitis bovine. The aim of this study was to develop an analytical method to identification and quantification thymol and carvacrol in milk and plasma of bovines treated with formulation.A method for the analysis was developed using gas chromatography-mass spectrometry (GC-MS) and solid-phase microextraction (SPME). The following chromatographic conditions were established: capillary column RTX®-5ms with temperature starting at 100°C (1min) and programmed to increase 10°C/min to 160°C (1min), helium flow rate of 1mL/min, injector and detector temperature set at 250°C and ionization by electron impact. To obtain the optimum extraction conditions, the procedure based on headspace-SPME (HS-SPME) was optimized and the following conditions were established: sample volume; 10mL of milk or diluted plasma (1mL plasma and 9mL of water), fiber of polydimethylsiloxane-divinylbenzene (PMDS-DVB), 1.5g NaCl, pre-heating the samples at 90°C for 5min with stirring speed of 540rpm, exposure of the SPME fiber in the headspace for 40min and desorption in the injector at 250°C for 5min. The analytical method was validated showing quantification limits of 0.5 and 2.0ng/mL for both analytes in plasma and milk respectively, and acceptable precision and accuracy.