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

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).