And as the above image shows the gas flow passes

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And as the above image shows the gas flow passes through the septum purge and the split vent. This configuration is called the split mode because some of the gas in the injector exits though the split vent. This means—and this is paramount—that some of the sample injected into the injector by the sample syringe will get vaporized and escape through the split vent. See below; the pink in the injector is meant to be vaporized sample.
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That lost sample will not go on the column (but to waste) and so is split away, ergo this is a split injection In this example, the split ratio is 1/49 because 49 parts are injected and 1 part goes on column. Again, this is a split injection. If the concentration of an analyte is high, say, 25 μg analyte/ μL—pretty high for capillary columns and 1 μL is injected, the analyst—that’s you—chooses the split injection mode and opens the split valve before the 1 μL injection is made. (With autosamplers and multiple samples this would be programmed into the method.) This means that the mass of sample actually injected (remember that the sample contains 25 μg analyte/ μL) would be 1/49 of that, that is, 25/49 μg analyte/ μL and this is about 0.5 μg analyte/ μL (actually 0.5102 μg injected but that’s to accurate to worry about given the slop in a 1 μL syringe). Again a 1 μL injector is made but only 25/49 of the mass injected goes into the column (on column) so it’s as if a 25/49 dilution has been made but the time required is only the software flip of the switch! Now that’s
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  • Fall '06
  • CHASTEEN
  • Chromatography, pH, analyte, injector, split injection, split vent, µg analyte/ µL

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