2.3. Sample extraction
Since explosives are polar analytes that exhibit high affinity
toward aqueous solutions and low vapor pressures [18],
immersion, rather than headspace SPME was selected as extraction
mode. Aqueous samples (25 or 35 mL) were thus extracted
by immersing completely a fused-silica fiber coated
with the sorbent phase of interest (Supelco) in the solution
that was stirred continuously with a Variomag magnetic stirrer
(ColeParmer Instrument, Anjou, Que.). Three different
fibers were tested for their ability to extract explosives: a 50-
m film of Carbowax/templated resin (CW/TPR); a 60-m
film of polydimethylsiloxane/divinylbenzene (PDMS/DVB);
and a 85-m film of polyacrylate (PA). Adsorption was conducted
at room temperature and stirring rate, concentration
of NaCl, fiber sorbent phase, and adsorption and desorption
time were optimized.