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.