Headspace solid-phase microextraction combined with comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry for the determination of volatile compounds from marine salt

Abstract

In this work, a methodology to characterise the volatile and semi-volatile compounds from marine salt by headspace solid-phase microextraction (HS-SPME) and comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GCxGC/TOFMS) was developed. Samples from two saltpans of Aveiro, in Portugal, with diverse locations, obtained over three years (2004, 2005, and 2007) were analysed. A 50/30microm divinylbenzene/carboxen/polydimethylsiloxane SPME fibre was used. The volatiles present in the headspace of the solid salt samples (crystals) were equilibrated overnight at 60 degrees C and extracted for 60min prior to injection in the GCxGC/TOFMS. 157 compounds, distributed over the chemical groups of hydrocarbons, aldehydes, esters, furans, haloalkanes, ketones, ethers, alcohols, terpenoids, C(13) norisoprenoids, and lactones were detected across the samples. Furans, haloalkanes and ethers were identified for the first time in marine salt. The large number of co-elutions on the first column that were resolved by the GCxGC system revealed the complexity of marine salt volatile composition. The existence of a structured 2D chromatographic behaviour according to volatility, in the first dimension ((1)D), and primarily polarity, in the second dimension ((2)D), was demonstrated, allowing more reliable identifications. The resolution and sensitivity of GCxGC/TOFMS enabled the separation and identification of a higher number of volatile compounds compared to GC-qMS, allowing a deeper characterisation of this natural product.