GC - Split/Splitless Gas Chromatography Injection Thomas G...

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Split/Splitless Gas Chromatography Injection Thomas G. Chasteen Department of Chemistry Sam Houston State University See http://www.shsu.edu/~chm_tgc/primers/pdf/GC.pdf for a PDF version of this document. The inside diameter and chromatographic film amount (the thickness of the chromatographic surface in the column) of modern capillary gas chromatographic (GC) columns dictates that the amount of injected samples (the mass of analytes inject on-column) is relatively small compared to packed columns . For instance, packed columns can handle tenths of milligrams (100s of micrograms) injected. For example, analyte peaks A and B can be successfully separated with masses of 200 µg A and 125 µg B and still get baseline separation (the chromatographer's holy grail). With packed columns this is all good. But capillary columns are much more easily overloaded: A and B need to be 20 µg and 12.5 µg at a maximum to be baseline separated if they're closely eluting (similar retention times). At masses much above this the chromatographic peaks are overloaded ( see here ) and overlap because all the chromatographic active sites in the capillary column's chromatographic surface are filled and additional analyte is not retained, vastly broadening the peaks. And for very small diameter capillaries (say, microbore, 0.1 to 0.05 mm diameter columns) the overload level occurs at even smaller masses 1 µg amounts). So capillary column require smaller amounts of injected analytes compared to packed columns (or the in-
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GC - Split/Splitless Gas Chromatography Injection Thomas G...

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