Optimization of Headspace Solid-Phase Microextraction and Static Headspace Sampling of Low-Boiling Volatiles Emitted from Wild Rocket (Diplotaxis tenuifolia L.)

Abstract

Emission of low-boiling volatile organic compounds (VOCs) is one of the first signs of a cascade of degradation processes taking place in leafy green vegetables after harvest. VOCs from fresh produce can be difficult to measure due to their high volatility, low stability, and variable concentrations. VOCs emitted from packaged wild rocket were selected for optimization of two sampling techniques: solid-phase microextraction (SPME) and static headspace (SHS) sampling. The selected compounds were acetaldehyde, dimethyl sulfide, nitromethane, 3-methylfuran, ethyl acetate, dimethyl disulfide, and hexanal. These compounds having different chemical structures, molecular weights, and boiling points were representative for the VOC profile of packaged wild rocket. The carboxen/polydimethylsiloxane (CAR/PDMS) fiber showed the highest extraction efficiency. For SHS analysis, injection of 750 μL of gas sample at 10 μL s−1 injection speed and 1:1 split ratio was optimal. High losses of dimethyl sulfide, dimethyl disulfide, and nitromethane (21–62 %) were observed during 20 h postsampling storage of the CAR/PDMS fiber prior to desorption. SHS sampling of VOCs and storage of vials for 2.75 h prior to GC-MS analysis also led to losses of volatiles. For analysis of VOCs naturally emitted from packaged wild rocket, the SPME and SHS sampling methods were complementary as they covered a broad concentration range from the lower parts per trillion (SPME) to the higher parts per million (SHS) ranges.