Chromatography Forum

Hi all,

Does anyone have experience in using a split plate that connects 2 different inlets to the GC Column and 1 outlet to the MSD?

The configuration on the GC-MS that I am using now is 2 injectors (Split/Splitless and PTV inlets) connected to the GC-MS via a 2-way splitter, i.e. 2 inlets and 1 outlet to the MSD. Therefore I had to optimise the inlet pressures to ensure that the analytes would not back-flow to the other inlet that I am not using. The final pressure setting I obtained was that if I were to use the front inlet, the front inlet pressure would have to be higher than that of the back inlet, or else there would be loss of peaks, and vice versa. Could anyone explain possible reasons on this because I was wondering if it should have been the other way round, meaning the back inlet pressure to be higher such that analytes would prefer to go through an inlet with lower pressure? The GC is in constant flow mode.

Thank you!

What about a 2 hole ferrule? If you system can handle it, and your column diameter.

eg:
5181-3388 Ferrule, 0.3 mm id, 2-hole, 15% graphite/85%Vespel, 0.1 mm column, 10/pk Two hole, 85% Vespel/15% Graphite 0.3

Hi all,

Does anyone have experience in using a split plate that connects 2 different inlets to the GC Column and 1 outlet to the MSD?

The configuration on the GC-MS that I am using now is 2 injectors (Split/Splitless and PTV inlets) connected to the GC-MS via a 2-way splitter, i.e. 2 inlets and 1 outlet to the MSD. Therefore I had to optimise the inlet pressures to ensure that the analytes would not back-flow to the other inlet that I am not using. The final pressure setting I obtained was that if I were to use the front inlet, the front inlet pressure would have to be higher than that of the back inlet, or else there would be loss of peaks, and vice versa. Could anyone explain possible reasons on this because I was wondering if it should have been the other way round, meaning the back inlet pressure to be higher such that analytes would prefer to go through an inlet with lower pressure? The GC is in constant flow mode.

Thank you!

When you say "loss of peaks" do you mean that all the peaks disappeared completely, some peaks but not others disappeared completely, or peaks got smaller ?

Peter

If you are using an Agilent 7890 or 6890 that calculates flows using the head pressure of the inlet then it can be a problem with the setup you are using because of the back pressure at the end of the columns. The GC is expecting there to be a hard vacuum at the outlet of the column instead of pressure there.

I solved the problem by using a 0.53 transfer line between the MS and the splitter, and using 0.18 or 0.25 analytical columns. With this setup the ends of the columns will see vacuum instead of high pressure. You can set the column you are using to normal flow rate and the other column to about 0.2-0.4 ml/min and thing will run fine. The unused column flow rate will depend on starting oven temperature and diameter, since for some flow rates it would require negative head pressure to get to 0.2ml/min as the GC calculates it, so just bump up the flow rate until you have a at least 1psi on the inlet at the starting oven temperature then set the active column at normal flow rate.

I have been running this setup on a 7890/7000 system for over a year now without any problems.