HEADSPACE SOLID-PHASE MICROEXTRACTION

Headspace solid-phase microextraction is a solvent-free sample preparation technique in which a fused silica fiber coated with polymeric organic liquid is introduced into the headspace above the sample. The volatilized organic analytes are extracted and concentrated in the coating and then transferred to the analytical instrument for desorption and analysis. This modification of the solid-phase microextraction method (SPME) shortens the time of extraction and facilitates the application of this method to analysis of solid samples. The detection limits of the headspace SPME technique are at ppt level when ion trap mass spectrometry is used as the detector and are very similar to that of the direct SPME technique. A simple one-dimensional kinetic model has been developed to study the diffusion process involved in headspace SPME. The results from theoretical modeling are consistent with the experimental data. In the experiments, a group of organic compounds, benzene, toluene, ethylbenzene, and xylenes (BTEX), and several polynuclear aromatic hydrocarbons (PAHs) in water were analyzed by the headspace SPME technique. The sampling time for BTEX was reduced to about 1 min compared to about 5 min for direct SPME sampling of the aqueous phase. At ambient temperature, the headspace SPME technique can be used very effectively to isolate compounds with Henry's constants above 90 atm.cm3/mol (i.e, three-ring PAHs or more volatile analytes) and can also be used to sample less volatile compounds if high sensitivity can be achieved without reaching equilibrium. The equilibration time for less volatile compounds can be shortened significantly by agitation of both aqueous phase and headspace, reduction of headspace volume, and increase in sampling temperature.