Use of solid phase microextraction in diffusive sampling of the atmosphere generated by different essential oils Original Research Article

This work describes the development and optimisation of a complete headspace-solid phase microextraction (HS-SPME) procedure for qualitative and quantitative analysis of the equilibrium headspace generated by a number of essential oils (EOs) with potential applications in active packaging, including basil (Ocinum basilicum), clove (Sygyzium aromaticum), rosemary (Rosmarinus officinalis), citronella (Melissa officinalis), and cinnamon (Cinnamonum zeylanicum). The method consists of a combination of fully exposed HS-SPME for qualitative analysis and diffusive HS-SPME for quantitative determination. First, complete optimisation of a fully exposed HS-SPME procedure was carried out by means of a combination of a Plackett–Burman screening experimental design and response surface modelling (RSM). The results were used to fully describe the atmosphere generated by the EOs and to select the most relevant compounds for further consideration. The fibres were then calibrated (i.e. the uptake rate was calculated) by exposing them to known concentrations of terpenes in closed extraction vials. With a sampling time of 30 min at 20 °C, uptake rates ranged from 2.2 to 3.3 pg (min ppbv)−1. Results were checked by sampling over extended periods of times, with the observed variation being less than 5%, despite a 10-fold increase in extraction time. The results were further validated by comparing the calculated diffusion coefficients with theoretical data. The ratios of experimental:theoretical values varied between 0.85 and 1.05. The sensitivity of the uptake rate to headspace concentration was also investigated; variation of less than 10% was observed despite changes in concentration of four orders of magnitude. The new diffusive sampling method proved to give robust determinations of all the test analytes (by contrast, HS-SPME failed for camphene, camphor and cinnamaldehyde), providing repetitivity and intermediate precision lower than 9% (the values for HS-SPME were 10 and 12%, respectively).