Hello Norbert:



When we use the shield plate, sometimes when the instrument won't start we will rotate the torch slightly to help make a better contact.  We have sometimes even bent the strip of the shield plate to ensure a good connection.  Is there any debris such as carbon inside the torch box?  That will cause problems as well as any deposits or corrosion on the polished brass inside.



Jay

-----Original Message-----

From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). [mailto:[log in to unmask]] On Behalf Of Norbert Kandler

Sent: Thursday, December 02, 2010 9:52 AM

To: [log in to unmask]

Subject: persisting plasma fluctation after ignition / Shield plate problem



We currently deal with the folowing problem:

Our ICP-MS is an Agilent 7500ce and we usually operate it with shield plate. Since severals days, it is not possible to ignite the plasma when the shield plate is mounted. The plasma ignits, immediately fluctates and generates noise synchron to the fluctations. We usually switch off the plasma within 10 seconds manually. Shield plate and torch are completely new, but problem persist. Without shield plate, the plasma is fine.



Any suggestions?



Thanks a lot

Norbert