So capillary column require smaller amounts of

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So capillary column require smaller amounts of injected analytes compared to packed columns (or the in- between megabore columns: 0.52 mm i.d). How is small injected mass accomplished? By dilution of highly concentrated samples, of course, to the lower the amount each contains per μL injected. But this is time- and analyst-intensive and analytical laboratories are all about efficiency. So this is where the split/splitless injector come in . Using merely a flick of a software-controlled valve the amount of injected analyte can be instantly varied before an injection is made . This is called the split ratio and is a function of the ratio of gas flows through the GC’s injector, all controlled by pressure/gas flows in the injector. Wait, wait it’ll get better. In older instruments this was carried out by manual control of gas valves. By in modern GCs this is all controlled by software and can be stored in the analytical method.
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The normal GC injector configuration is below. In this example, a total flow of 49 mL/min comes into the injector from the pressurized carrier gas tank (He is most common; N 2 is cheapest but chromatographically less forgiving). Note that the total gas flow flows 1) through the column ( green thing at bottom ), 2) out the septum purge, and 3) out the split vent and always add up to the incoming flow (49 mL/min in this example). So 1 + 2 + 46 = 49 mL/min.
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  • Fall '06
  • CHASTEEN
  • Chromatography, pH, analyte, injector, split injection, split vent, µg analyte/ µL

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