Headspace Solvent Microextraction

A hanging microliter drop of 1-octanol is shown to be an excellent preconcentration medium for headspace analysis of volatile compounds in an aqueous matrix by gas chromatography (GC) or gas chromatography/mass spectrometry (GC/MS). Model compounds benzene, toluene, ethylbenzene, and o-xylene (BTEX) are conveniently and rapidly preconcentrated in the microdrop. An internal standard, decane, is present in the organic extracting solvent, and linear calibration curves of relative peak area versus aqueous concentration are obtained for the four model compounds. Detailed kinetic studies reveal that the overall rate of mass transfer is limited by both the aqueous-phase stirring rate and the degree of convection within the organic phase. The very low vapor pressure of 1-octanol results in minimal evaporation of the microdrop during the extraction time. This system represents an inexpensive, convenient, and precise sample cleanup and preconcentration method for the determination of volatile organic compounds at trace levels.