Counts going down ICP-MS 8900 during 2 hours test

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).  

Hi! thanks for the answer.

I checked that contacts from a reply what I saw before. maybe it was from you also? They seem ok.

Indeed, the lenses had been cleaned and Extract 2 went to -180 -220 range.

Extact 1 is never 0. Agilent said the same to us, that it should be 0. And their solution was that we needed to "force" it to be 0 during start up, but sadly it needs a newer version of Mass Hunter.

Since we're talking about lenses cleaning: that last clean also lowered the doubly charged considerably, but the oxide ratio keeps being high. Any suggestion about this?

Hello,

No worries for the extract 1 to be tune.  You have a MSMS or 8900 ICPMS so it's normal behavior to tune the extract 1 lenses.  

You counts are low.  So you have intro problem.  What are the counts of mass 56, 80 and 12.  Are they low also.  56 should be in the 50K on screen (0.1 integration) and 80 should be around 200K.  If you can tune EM with mass 80 correctly then your counts level are good.  Seem really the skimmer could be the issue.  It's really simple to try a brand new skimmer.  Shape of plasma ions is critical for higher sensitivity.  But again it's could be other issue with not grounding properly.  And recommend to call the response center for more help. 

Hi, thanks for the answer.

Sorry, in which occation do you mean for counts of 56,80 and 12? You mean while using the 1 ppb tuning solution with peripump 0.1 rpm?

"If you can tune EM with mass 80 correctly then your counts level are good"

What do you mean by that?

Hello,

You can monitor the plasma gas itself.  You don't need tune solution.  The plasma is always composed of Carbon (12), Argon Oxide (56) and Ar2 (80).  You can monitor in tune screen these counts level to see if this is intro issue or other issue.  If these 3 masses are low.  Then you have intro problem or ground problem.

When you perform the EM the default is mass 80.  it needs 200K on screen to tune the EM.  So, it's always a good indication that the plasma gas is going correctly into the system.  

Also make sure after cleaning the cones that you condition them before use.  This will improve stability of counts on the long run. 

Thank you very much.

We actually monitor mass 56 (among with others) at the beginning of each session because mass 56 counts start at around 30-70 K (skipping warm up, just when the plasma lights up) and go down till ~500 counts in around 20-40 minutes. We do that to make sure that the mentioned variation of plasma composition is before the sequence. I think the presence of ArO is a source of air contamination, cylinders of Argon shouldn't have much of it inside.

I'm going to check mass 80 and perform the EM auto setting.

Thank you very much.

We actually monitor mass 56 (among with others) at the beginning of each session because mass 56 counts start at around 30-70 K (skipping warm up, just when the plasma lights up) and go down till ~500 counts in around 20-40 minutes. We do that to make sure that the mentioned variation of plasma composition is before the sequence. I think the presence of ArO is a source of air contamination, cylinders of Argon shouldn't have much of it inside.

I'm going to check mass 80 and perform the EM auto setting.