Split inlets

Fig. 14.4. Schematic diagram of a split inlet for capillary GC showing the pneumatics and major components. Reprinted with permission from the 6890 Gas Chromatograph Operating Manual. Copyright (2004), Agilent Technologies.

Pressure regulator. The split inlet is back pressure regulated to ensure a constant head pressure, therefore, a steady flow through the column. For capillary columns, the inlet pressure determines the column flow, as per Eq. (14.11). As the inlet operates, the split vent can be opened or closed or upstream gas flow may change the regulator maintains the desired pressure, therefore the desired column flow. 

Fig. 12. Schematic illustration of hydrodynamic relaxation achieved in a split inlet system (iabove) and a frit inlet system (below). Reproduced from [160] with kind permission of the American Chemical Society...

A Varian 3400 GC is used as a platform. I split inlet, FID flame ionization detector, C microfabricated column. The two detectors can be used alternately [2]... 

On using split inlet systems the injection of small sample volumes will provide very go results however, direct injection without splitting was not successful. 

Flush. A clean purge flow of carrier gas travels through V2 and splits between R2 and R3. Residual sample in R3 is swept onto the trap and purge flow through R2 eliminates any memory effect or sample carryover from the split inlet. 

The splitless inlet, which employs the same instrumentation as the split inlet, provides a means for improving sensitivity by transferring nearly the entire injected... 

The temperature of a split inlet should be set high enough such that there is enough thermal mass and energy in the inlet to vaporize the injected sample... 

When using a split inlet, there are several flows that provide the exact injected sample amount. The most important of these is the split ratio, which is the ratio of the volumetric flowrate at the split purge vent to the volumetric flowrate in the GC column. Classically, this was measured manually, using a flowmeter to obtain the purge vent flow and by injecting a nonretained substance to obtain the column flowrate. With electronically controlled systems, these values are... 

The formation of phenyl benzoate was both unexpected and inexplicable. GC-MS fragmentation patterns of pure benzoic acid anhydride dissolved in dried toluene indicated the presence of phenyl benzoate. It is possible that due to the high split-inlet temperature (250°) in the gas chromatograph, the anhydride decomposes to the ester with the loss of CO. 

Sample Introduction System—Any system capable of introducing a representative 0.1 to 1.0-pL liquid sample into the split inlet device of the gas chromatograph. Microlitre syringes, autosamplers, and liquid sampling valves have been used successfully. The split injector should be capable of accurate split control in the range from 10 1 to 500 1. 

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