turning off of MS vacuum pump to conserve gas?

[slentz]

Hi,

I just started at a new lab and they have a practice I haven't encountered before.

Every Friday they power down the Agilient 1100 MSD and turn off the vacuum pump to conserve Nitrogen?

Other then the start up time on Monday morning, is there any reason that this practice may not be good? In the other labs I have worked at the MS pumps were only ever turned off for servicing.

Thanks

[bhuvfe]

I'm not familiar with that instrument but the procedure seems
very strange to me (I would expect the oil of the foreline pump
to contaminate your MS eventually...).

Are you sure that you don't simply switch the N2 of the nebulizer
and not the foreline pump?

[Camisotro]

Seems odd to me as well... how much pumping down under vacuum is needed to get it back into shape? In my lab, if the MS has been shut down I am asked to give it at least 8 hours under vacuum before I start using it.

[lmh]

It's an awfully bad idea. I'd imagine it doesn't do the turbomolecular pumps any good at all. Turning them on and off is the most stressful part of their life, and they are one of the most expensive components in the instrument.

You could just turn off the nitrogen supply. This isn't recommended by Agilent as the instrument will then gently suck air in through the capillary, and your air may not be as clean as your nitrogen - but it's probably less harmful than turning off the entire instrument.

And yes, of course, it does mean you shouldn't be working on Mondays while the instrument recovers its vacuum. Many of us would consider this a beneficial side-effect.

[Tomasz]

I was working in a similar lab a few years ago. The Hewlett Packard 1100 MSD had to be turned off on weekends. However, it was because of safety reasons. And there was only one problem with Monday analyses. I had to start them a few hours later than usually. 1100 needs some time before you can make its calibration. I am not sure but as I remember 2 hours was enough. You can prepare your standards and samples during these 2 hours. Nevertheless, I certainly agree with lmh - it is not a good idea for the turbomolecular pumps.

[sam.pedraglio]

I'm completely agree with Imh regard the stress to the turbo pumps and, if I'm not wrong, the first part of the ion transfer line of the 1100MSD should be similar to our Bruker ITrap, in this case you could avoid to suck air using a septum at the entrance of the capillary.