Analysis of vitamin K in green tea leafs and infusions by SPME–GC-FID

The usual methods for determination vitamin K are laborious. With the aim of replace them by a simpler method that requires fewer solvents, lower analytical levels and allows reporting of results in a smaller period of time, a procedure based on solid-phase microextraction (SPME) and gas chromatography with flame ionization detector (GC-FID) was developed. This method was used to analyse vitamin K in green tea leafs and infusions from nine brands of green tea commercialised in Portugal.The best analytical conditions were obtained using PDMS 7 μm fibre using immersion extraction at 40 °C, for 45 min and 1300 rpm. The linear range for vitamins K1 and K2 was defined. The detection limits obtained with PDMS fibre and GC/FID were 0.16 and 0.07 mg/L for vitamins K1 and K2, respectively.In all analysed infusions the concentration of vitamin K was lower than the detection limit of the developed method, however, the concentration of vitamin K1 present in tea leafs was between 120 and 625 μg/100 g.