The ICP-MS 7900 Performance channel counts are constantly fluctuating with the Li count trending down over time before cleaning takes place. What's interesting are the inconsistencies observed with Y and Tl. These results were observed after a service visit. The cones were cleaned with no jagged edges, nebulizer checked, tubing, graphite gasket, torch and shield replaced but I continue to have this problem. Aside from replacing the EM and calling support not sure what else to investigate.
Hello,
For the most part, your counts are very low except for a few flyers. In your message you said you "checked the nebulizer", how did you check it? This is the most common cause of low signal, have you tried a new nebulizer?
What type of sample introduction do you have? Quartz or PFA inert? Do you have an ISIS3?
Which Autosampler are you using?
Do you use the third channel to pump in the internal standard (ISTD) solution? If so, do you leave it in the ISTD solution when you light the plasma? What is pumping through that line when you tune?
With the plasma off, run the lens shortage test. Go to Task Navigator pane on the left side, Hardware/Dashboard. Click the large Icon of the Ion Lenses and select Maintenance. There is an entry above the table that says Start Shortage test, run this and look for errors. If there are some, try a new lens stack. When your remove the lens assembly, check the contacts that are in the interface once you remove the lens stack.
Check the contact on the torch stand where the Pt shield touches when you install the torch.
A bad, missing, or incorrectly installed Pt shield could cause low sensitivity. The shield should wrap around the torch inside the bonnet. There are 2 glass nubs, if installed on the one to locate the torch in the stand it would not be on the torch inside the bonnet, therefore not in the work coil when installed in the stand.
