Split ratio

Discussions about GC and other "gas phase" separation techniques.

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Currently working on a method that requires a split ratio of 0.1:1. That probably seems quite low (propably because it is). Somehow this got validated and up to a point it seemed to work fine but now anytime I try to run samples the inlet pressure slowly goes down until It shutdown completely.

Can anyone tell me why this is happening? Does it mean that for every one part of sample injected that 0.1 enters the column and the system cannot cope with this setting. what variables can be changed (other than the split ratio) that could stop/help this shutdown from occurring.

I know my wording probably sounds a bit novice but I would like to understand what is going on for my own piece of mind. Thanks
On my P&T VOA system I may run a 30:1 split. 30/31 of the flow is diverted out the split vent and 1/31 is sent down the column or approximately 30 mL/min out the split vent and 1 mL/min down the column.
Yours would be 0.1 mL/min out the split vent and 1 mL/min down the column for a total flow of 1.1 mL/min.

Split ratios less than 5:1 can be unstable in my Agilent system. Could the method actually have a split of 10:1 so that 10/11 of the flow is out the vent and 1/11 down the column?
I doubt that the split ratio really is 0.1:1, probably it is 10:1 - which will put 10% of the sample onto the column, and vent the rest through the split.

A slow pressure drop as you describe is probably due to a leak somewhere, especially if you are running at constant flow which requires an increase in inlet pressure as the oven heats. As the increase in pressure increases the loss through the leak you get to a point where there is too little gas going into the inlet to sustain the flows out of it.

So, you need to check for leaks with a leak seeker, and then fix them.

Peter Apps
3 posts Page 1 of 1

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