Counts going down ICP-MS 8900 during 2 hours test

Question

Hi everyone. 
 We've been experiencing some trouble with our equipment, as detailed in: Low sensitiviy and change in cps through time ICP-MS 8900 
 We already polished and cleaned lenses, cleaned introduction system, and the sampling and skimer look alright. We also opened the vacuum chamber and closed it (without any further modifications). 
 
 Now remains a different but pre-existan problem The last 2 reports had decent sensitivity but CPS go down all the time. This are the results of a test indicated by Agilent:

Solution is 1 ppb tuning, and is being pumped all the time without an autosampler, like this:

Any ideas, suggestions? Is it a normal behaviour? I don't think so. 
 Thanks

Tom Herzog · Answer

In looking at the report it looks like you have the x-lenses installed. Typically Extract 1 is set to zero on those, only s-lens do we apply voltage to Ext1. Also, extract lens 2 is maxed out at -250. How often do you clean the lenses? When the voltages start going high like that it is time to clean or replace the lens if you cannot get it more positive than the -250V limit. Typically runs around -200V on a well used instrument. 
 Check the condition of the lens contacts in the interface. They may need to be cleaned off with sand paper and polishing paper (blue and yellow sheets that ship with the instrument).

Counts going down ICP-MS 8900 during 2 hours test

Top Replies