Sodium counts are increasing.  How to I manage/control this



I am running a 7800 ICP MS for EPA 200.8 method.  I have noticed the pass number of months the sodium counts during my warm-up and shut down are running in the 50,000 to almost 100,000 counts.  After 30 mins to 2 hr  (warm-up or rinsing) the counts drop  very little. Also the last few  EPA tune report shows a large peak next to mass 24  (left side) in the Resolution/Axis section of the report which I'm assuming is mass 23 (Na).    We use ultra pure acids and water (18.2 Mohms).  I understand we can not get rid of Na completely. Are there any suggestion on how to control/decrease the Na counts?


I attached a copy of the EPA Tune Check report to show the large Na peak that runs on the left side of mass 24.


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