Chromatography Forum

Hello,

We need to purchase a new GC/MS and I ask myself a question : is there a real difference of sensibility between a diffusion pump and a turbo pump ? (In fact, Agilent told me "no difference as long as you use EI" and Thermo says "with a turbo pump, your sensibility will be better"....)

Thank you for your help !

Give both companies a low concentration test sample and tell them to run it, then compare the results.

Peter

Your "real" pump down time, to remove moisture and air from the MS, will be substantially faster with turbo as compared to diffusion, at least with Agilent. So if you need to change columns routinely, consider turbo.

We have six Agient 5973/5975 detectors. Five are turbos and one is a diffusion pump. In the last 10 years, the only one that has ever had oil backstream into/onto the analyzer/rail is the one with the diffusion pump.

Schmitty,

What are the relative maintenance costs on the different types of pumps?

How long does a turbo pump last before it needs a refit?

Or do you have service contracts where these things are replaced on a routine basis and such things are not a concern for you?

I had thought diffusion pumps needed much less maintenance, but I might well be wrong or out of date on this issue.

Thanks

We have two Agilent MS, one turbo and the other diffusion. The turbo has been running for more than 9 years and no pump maintenance has been necessary. According to Agilent, the oil in the diffusion pump should be replaced regulary, but to be honest I have never changed the oil in my diffusion pump (that's about 14 years). I have experienced some problems with the thermal switches in the diffusion pump, one checks if the oil is hot and the other shuts down the oil heater if it is too hot. In case of malfunction the MS won't allow you to inject samples although replacing them solves the problem but there's some downtime involved.
I completely agree with Consumer Products Guy in that pump down with a turbo is faster (typically in 4 hours at most you can inject your samples).

Schmitty,

What are the relative maintenance costs on the different types of pumps?

How long does a turbo pump last before it needs a refit?

Or do you have service contracts where these things are replaced on a routine basis and such things are not a concern for you?

I had thought diffusion pumps needed much less maintenance, but I might well be wrong or out of date on this issue.

Thanks

The diffusion pump oil is relatively cheap, and the intervals at which we change it make the price insignificant.

We have had one of the 5973s have the turbo "go out" twice in the last 10 years. It was $6-7k to replace it each time. I think the average lifetime of the turbo is supposed to be 3 years according to HP/Agilent.

For EI, I prefer a diffusion pump. Silent and long lasting, low costs.
But the modern turbos are much better than the first generation, so it doesn't matter that much.

I must have jinxed myself. I had a turbo fail on another of the 5973 systems.