Chromatography Forum

When I try to measure H2 flow out of FID, I found few H2 comes out from FID, Most of H2 flows into the collum and comes out from split purge. Why this happen and what is the problem? Thank you!!

Since you are using split to your column, depending on the split used, you will have the splitted part of your flow into the column and then detector, and part to split vent.

Let's say 10 ml/min, split 1:10, you will have 1 ml/min at the end of the column (FID) and 9 ml/min in split vent...

This sounds very very unlikely to me but not quite impossible. If the flame tip is blocked, and you have a very short column installed it is just conceivable that you get back flow from the FID through the column to the inlet and out through the septum purge.

To be completely sure that you are measuring the hydrogen flow to the FID supplied by the detector gas controls of the GC, remove the column from the detector and seal the detector connection where you took the column out. Then measure the hydrogen flow at the detector - it should be around 30 ml / min. While you are about it you should check the make-up and air flows as well. Once you have them adjusted correctly, remove the plug and reconnect the column.

If you cannot get the hydrogen flow that you need by adjusting the controls on the GC, check that you have adequate pressure in your hydrogen supply. Also make sure that the flame tip is not blocked. If you have an Agilent GC the flame tip has to be matched to the column diameter or the column can block the flow of hydrogen.

Good luck. Peter

Be sure you are using the proper adapter to measure flow. Most FIDs come with an adapter that has to be inserted into the top of the detector to be able to measure flow properly. If you just put a flow meter at the top of the detector you will probably not be able to measure the flow properly due to leaks.