Gas Chromatography

[Deng]

Does anyone know what the purpose of the split flow does? And where I can get more information on it. I'm writing a training module and need more details on split flow. Is it the same term as the split injection?
Here is how I define the two.

Split injection: It involves vaporizing the sample in a gas stream using a flash heater and subsequently splitting the gas stream at a ratio of 100 to 1 or more so that only 1 % (or less) of the sample, passes into the capillary column, whereas the remainder passes to waste.

Split flow: to clean the injector of residual sample and helps reduce contamination in the inlet . Or does it do more than just clean the inlet?

Is this correct??

[chromatographer1]

I would describe split injection and split flow in slightly different terms.

Split injection:

Split injection involves vaporizing the sample injection in a carrier gas stream using a flash heater and subsequently splitting the gas stream at an adjustable ratio ( most commonly from 5:1 to 500:1 ) between the analytical column and a vent to waste. This is done to avoid overloading the sample capacity of the column and to minimize the width of the sample plug introduced onto the column.


Split flow:

The flow of carrier gas to vent from a split injection port. This flow is adjusted to change the amount of sample placed onto an analytical column from a vaporized liquid sample injected into a carrier gas stream in an injection port of a gas chromatograph.

Total carrier gas flow is the sum of the gas flow through the column and the split flow from the injection port.

The split flow does not clean the injection port per se. It simply allows the heated sample to reside a minimal time in the injection port. This minimizes the thermal decomposition buildup of samples within the injection port and sends most of the bleed from deposits in the injection port to waste instead of onto the analytical column.

best wishes,

Rod

[Deng]

Rod,

Thanks for making things clearer. I was just confuse on the purpose of the split flow and got some wrong information from other websites.

[CE Instruments]

Rod total flow is usually column flow plus split flow plus septum purge flow

[chromatographer1]

Absolutely right.



Today most GCs do have a septum purge. Back in the day they didn't and I still forget that little detail. GUess I am dating myself but if the ferrule fits....................

Thanks for the correction.

(and don't forget the leak of the septum after you forget to replace it after 100 injections or so )

Rod