James_Ball wrote:Just noticed your location after the Pitino comment, we are only about 150 miles away
Diffusion pumps are also better if you want to use hydrogen carrier, they pump it out much more efficiently than the turbos do. I always let my diffusion pump instrument run overnight after venting before I even try to calibrate, even better to do maintenance on Friday and calibrate on Monday, otherwise I am calibrating a few days later due to the final stabilization over a couple days.
Turbo pumps shine if you are needing to run more than 1ml/min flow rates or have to clean the source often such as when doing 8270/625 waste water samples. I have to say though, in 27 years I have only had to replace two turbo pumps on Agilent MS, one 5970 and one 5973, and each was over 10 years old. We did have an ICP/MS that was eating them up quickly for a while, but other than that no problems with them.
Yes, I'm at the big red school
In any case, the comment about H2 and diffusion pumps is interesting. I'll have to spend some time thinking through that one-I could see it being a case of the H2 molecules being too small for the blades to "catch" them effectively.
I too have been to some Agilent seminars on using H2, and I'm sold on it although I haven't tried it. The Saturn is a likely candidate if I ever get it going again. Aside from needing a new electron multiplier, its rough pump is currently in service on my 5975 while I wait on our scientific instrument tech to rebuild the pump that came with that instrument. Since the mass spectra from that instrument always have and always will look weird relatively to library spectra(thanks to it being an ion trap and not a traditional quadrupole), I don't think it would matter too much for that instrument.
There again, I'll go back to the fact that I've never dealt with an Agilent MS with a turbo pump, so don't know anything about their reliability. I've actually been keeping my eyes open for a 5970 for a couple of reasons, not the least of which is that they're quite inexpensive these days, although I don't know if it would be a great investment for me unless the price was free or pretty darn close to it. There's an out of service 5890/5971 in the department that I've asked about, but the owner isn't QUITE ready to let it go(and I think it's a diffusion pump-not sure if I've ever seen a 5971 with anything else).
Our MALDI-TOF is a bit of an interesting case. It's closing in on 20 years old, and you could probably count the time it's been open/vented in that time period in days. Even though-in theory-keeping an MS under vacuum is one of the best things you can do for it, that much time does take its tole on an instrument. We actually have two identical units sitting in the room with it-one is PROBABLY good enough that we could actually put it into service(it will pump down to where it should go, and the laser is strong) but hasn't actually been tested since we don't have a spare computer to connect it to and really don't want to disturb the working one. With that said, the top turbo pump(the one attached to the reflectron) has a TERRIBLE whine on the in-service instrument, and one of the PIs who looks after the instrument doesn't want to change it until it dies completely-if it were me I'd rather go ahead and stick a known good one on it since-with the way it current sounds-it's not an "if" but a "when" it goes. That's really outside my jurisdiction, though-I just advise/assist when something does break on it.
Unfortunately too for me, ANY maintenance(scheduled or unscheduled) on the GC-MS is a problem. Some PIs and grad students expect 25/8/366 availability of the instrument and can get really upset if it's down. It was enough of an issue that my predecessor finally told one to buy his own. He bought an identical 7820/5975, but now they STILL want use mine because they can't be bothered to do basic maintenance(they've called me about problems before, and I've pulled out inlet liners that I was halfway tempted to save because I've NEVER one look so bad-and they don't even realize they're there-much less doing things like source maintenance on it). I also have another faculty member who constantly brags about how "wonderful" his Thermo GC-MS is and about how it can "see things you can't see on an Agilent." I suspect that if he ran his samples on MY 5975 and not the other(poorly maintained) one in the department it would do just as well, but that's something not worth fighting.
In any case, where I was going with that I'd rather do service during the week where I can actually monitor it and actively keep people away from it even if I'm dealing with a barrage of "when will it be ready again?" If I did maintenance and then a pump-down on Friday, people would try to use it Friday night or Saturday and then complain about how bad their results were. That's also why I want another instrument that's at least reasonably similar(specifically a 597x instrument)-the spectra should be close enough to the 5975 that they can compare their results, and of course both would have a 30m/.25mm HP-5/DB-5/whatever-5 column.