A reliable method of sample introduction is presented for online gaschromatography with a special application to in situ field portableatmospheric sampling instruments. A traditional multi-port valve is replacedwith a valveless sample introduction interface that offers the advantage oflong-term reliability and stable sample transfer efficiency. An engineeringdesign model is presented and tested that allows customizing thispressure-switching-based device for other applications. Flow model accuracy is withinmeasurement accuracy (1%) when parameters are tuned for anambient-pressure detector and 15% accurate when applied to a vacuum-baseddetector. Laboratory comparisons made between the two methods of sampleintroduction using a thermal desorption aerosol gas chromatograph (TAG) showthat the new interface has approximately 3 times greater reproducibilitymaintained over the equivalent of a week of continuous sampling. Fieldperformance results for two versions of the valveless interface used in thein situ instrument demonstrate typically less than 2% week responsetrending and a zero failure rate during field deployments ranging up to 4weeks of continuous sampling. Extension of the valveless interface to dualcollection cells is presented with less than 3% cell-to-cell carryover.
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