An Almost On-Column Injector for Capillary Supercritical Fluid Chromatography

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Abstract
A simple modification to a commercially available four-port valve allows it to be used with a gas chromatographic on-column syringe for the direct injection of liquid samples into a short retention gap connected to a standard 50-µm i.d. supercritical fluid chromatographic (SFC) column. The resultant chromatographic peak shapes compare favorably with those achieved using more traditional split injections. Postinjection solvent venting eliminates the broad solvent peaks normally associated with splitless SFC injections without causing loss of nonvolatile (e.g., >C20 alkanes) analytes. Peak areas of individual components have relative standard deviations of ca. 10% for replicate injections, and with the use of an internal standard, the relative standard deviations are reduced to ca. 2%. Because volumes as large as 0.5 μL can be injected without the need for sample splitting, more dilute samples can be analyzed and flame ionization detection (FID) limits below 100 pg injected on-column (200 ppb w/v) for alkanes are achieved. The fabrication and use of the almost on-column injector for SFC with FID is reported.

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