Chromatography Forum

I'm re-plumbing a series 2 5890 without the EPC module to use hydrogen as the fuel and carrier. on the line in from the hydrogen generator I am going to put a t fitting, from the t fitting I will run the hydrogen to the carrier regulator and to the hydrogen regulator that are mounted on the inside left hand side of the instrument.

Previously the instrument was set to run helium as the carrier and aux gas. A t fitting split the helium after the regulator and ran to the aux control know and the total flow knob.

My question is that if I want to use helium as a makeup gas should I run straight from the tank to the aux inlet on the front panel? If so what is the max pressure that i can run into the the aux gas control on the front panel? ? I do not have a regulator in the 5890 for make up / aux gas like I do for the carrier,air, and hydrogen, thus I will have to control the helium pressure via the regulator at the tank, which currently also supplies helium to a 6890/5973.

Currently the helium tank regulator is set at 100 psi.

I understand that I can adjust the aux gas flow on the 5890 via the small set screw inside the aux gas knob, but I can't find anything saying what the incoming pressure limit is. I don't want to blow any seals or cause damage by running to high of a pressure into the aux gas inlet.

Below is the current setup using helium as carrier / makeup
and hydrogen and air running to the fid.

the other picture is my proposed change to use hydrogen as fuel / carrier and helium as makeup.

I will be running 15m-30 m capillary columns on the instrument.

My final question is how important is the make up gas? I've ran hydrogen as carrier and fuel in other instruments using capillary columns without a makeup gas and with a makeup gas and did not see any differences in the chromatograms. I don't know however if not using a makeup gas could lead to more maintenance of the jet or fid detector.

For make up gas to do any good it needs to be nitrogen - its function is to slow diffusion at the base of the flame, and helium is not viscous enough. That is why you did not see a difference with makeup and without.

With no makeup it is important to have the end of the column inside the stem of the flame tip so that the sample is swept rapidly into the flame by the fule hydrogen.

Peter

Yeah, when I converted a 6890 from helium carrier/make up gas to hydrogen carrier, I also went to nitrogen as the make-up gas. This worked great by the way, and very little updating of conditions was required.