Methodologies of quantitative headspace analysis using vapor phase sweeping Original Research Article

A headspace sampling technique that allows for the total or partial sampling of the vapor phase from a pre-equilibrated headspace vial is presented. The flow generated via a dual needle system through the headspace vial, can be directed either to the front of a GC column, to a sample loop, or through a trapping system that can be thermally desorbed onto a GC column. Unlike dynamic sampling, this methodology is free of problems associated with bubbling, and unlike regular static sampling, it is not limited to small aliquots. The theoretical treatment of dual needle sampling shows that the maximum mass (Mmax) of an analyte in the gaseous phase (Mg) is generated when the gas/condensed phase ratio (Vg/Vc) in the equilibrated headspace vial is equal to the square root of partition coefficient (K). Mg=Mmax at VgVc=K0.5A second needle was installed into a commercial static headspace autosampler to provide for this “sweeping” type of sampling. Several configurations of the automated headspace instrument with dual needle sampling capabilities are presented in this paper. The advantages of the method are demonstrated using the determination of low ppb (1×10−7%) of butadiene, butylenes, and isoprene. This technique was also applied to the determination of acrylonitrile, vinylcyclohexene, styrene, α-methylstyrene, aromatic hydrocarbons, formaldehyde, and several acrylates in polymers and other solid samples directly without the use of any solvent. Moreover, the technique generates favorable conditions for near complete removal of analytes from condensed matrices (FET methods at K⪡Vg/Vc). This, in turn, simplifies quantification and minimizes matrix effects. Special attention is given to quantitative analysis with this type of sampling using the method of standard additions for verification. The technique was also successfully used in conjunction with an electronic nose and a cold vapor mercury analyzer where a continuous sample flow or large sample volumes are desirable.