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

Hello,

 

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.

Thanks

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  • OK, the Performance tune and two tune checks are from post maintenance.  I normally do pre and post maintenance on batch .

     

    Pre-run Maintenance (before a run):

     

    ·         replace all peri-pump tubing.,

     

    ·         rinse/soak Spray chamber and connector tube in 5% HNO3 for 3-5mins, rinse with lots of water and air dry or switch to clean ones,

     

    ·         sonicate cones in ultra-pure water for 5 mins and dry with Argon gas.  (note: current cone has only been used once in September.  They were conditioned with Ca solution prior to use)

     

    ·         Run 1% HNO3 through sample probe and ISTD lines and monitor for Na, ISTDs, Sb, Mo and other few elements and try to drop down the counts to less than 1000.  However, Na and Sc always >1000 counts

    Post run maintenance:

     

    ·         Run 1% HNO3 for 30 mins to 1hr, until I start seeing the counts drop below 1000 counts (Na & Sc do not drop very much.

     

    ·         Run ultra-pure water for 30mins and then turn off the plasma.

     

     

    I’ll go ahead and sonicate again but will not be able to run until Saturday.  My work schedule is Sat to Wednesday. I will send you an update over the weekend for you to view Monday morning.

     

    Thanks,

    Jackie

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