Developments in the Analysis of Headspace Volatiles: On-Column Injections into Fused Silica Capillaries and Split Injections with a Low-Temperature Bonded PEG Stationary Phase

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Abstract
The injection of headspace samples directly into the interior of small bore capillary columns offers several advantages; one of the more important is that additional dilution of the sample by carrier gas, especially during its transport to the column, can be minimized. Even so, chromatographic results are usually improved if the sample band is narrowed or focused before it begins the chromatographic process. This is particularly true for headspace injections and for purge-and-trap methods. For some samples, properly executed headspace injections can yield results that rival, and are often superior to, those obtained by conventional purge-and-trap. Headspace samples generally contain appreciable quantities of water and, under normal conditions, are dominated by lower molecular weight compounds. Although some polysiloxane-type stationary phases can tolerate repeated water injection, the low retentions exhibited by most low molecular weight polar compounds on these phases complicate their analysis. Polyethylene-glycol phases generally possess higher polarities and greater affinities for such compounds, but they are susceptible to water deterioration at lower temperatures and possess relatively low high-temperature limits and (more important to the present study) high low-temperature limits. Partly in answer to these complications, aqueous samples containing such solutes have been subjected to headspace or purge-and-trap sampling in order to strip the polar solutes from the aqueous matrix. Recent developments in fused silica columns coated with water resistant and chemically bonded polyethylene glycol-type stationary phases that remain liquid under subamblent conditions offer the simplicity of split injection for the analysis of low boiling polar molecules in aqueous systems.

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