Elan 9000 High Background

I was looking on the forums because we've been having a problem with high background counts lately on our Elan 9000 ICPMS machine and I came across a few posts that kind of address our problem but don't ever really get right to the point.  Anyway, we've been running aqueous samples that contain trace metals for a little while now and saw that on the Daily Performance Report our background counts slowly started increasing. We're aware that this happens due to cones getting dirty and what not so we cleaned those and reinstalled them and all of the other parameters checked out but our background is still high. We had purchased a new set of cones and have tried to use them twice now but the Daily Performance Reports are always worse than if we just remove the original cones, wash them, and then reinstall them. Is this common?
I run a 1% nitric acid/0.5% hydrochloric acid solution during the 30 min warm up each day so the intro system should be clean and I recently changed out the roughing pump oil and allowed it to pump down over the weekend; still, the background counts are high. Should the nitric solution be run at a different time and is this concentration strong enough? In a couple of different posts on the forums, it was said several times that vacuum issues might be the problem and to check and make sure that there are no leaks. I've only worked on this machine for a few months so I'm still not sure about everything and I really don't know how to check the vacuum system to make sure there are not leaks, but I'd like to eliminate that as a potential source of irregularity. Do any of you guys think this is a possibility? Also, one of the posts said to check the vacuum pressure that is generated before and after the machine is running but I'm not even sure what "normal" readings would be.  Could someone explain to me (in laymen terms) exactly how to check the vacuum system? Any and all help would be greatly appreciated. Thanks for your time.

Mike

This seems to be a rare problem and I had trouble finding help with this problem also. You need to clean/change you DP aperture. This is the disk that sits behind the cones that is held between two plastic pieces, that postition MUST be straight....if you check and it is you could try to clean it and turn it around, but I wouldoder a new one for backup. If you do et it to work, it will only be a matter of time until you need a new one.

Hey, thanks for responding! I looked in the Hardware guide for the Elan 9000 and it goes through how to remove and clean the DPA but it says to unscrew the ion optics chamber lid that houses the DPA and I'm not sure which chamber that is. I could just open up both chambers and see for myself but that introduces more possibility for contamination so I'd rather just open the one that houses the DPA. Thanks for your help.

The DPA is in the same chamber that you would open to clean the lens. You must unscrew the fitting that is directly behind the lens and the dpa, which is a thin metal disk,  it is held in place by a plastic piece. After you clean/replace the dpa make sure you screw it back in perfectly straight.

Thanks sooo much for your help with this. I cleaned both the DPA and the lens yesterday and then reran my Daily Performance Report and the background came down significantly!!! Worked like a charm ;)

Riverbrat can you get me the part number for the differential aperture?  I have clean mine before, but I think it is time for a new one.  Thanks!