high silver 7500

Hello,

 

We have been seeing a very high background for silver during analysis. Instrument is a Agilent 7500 ICP-MS with chemstation. The instrument has has a lot of troubleshooting/maintenance and some of the things done include general cleaning ( nebulizer, spray chamber, torch, cones), also put in service new cones, new torch , new o-ring, torch box was replaced, RF generator swapped out a month or so ago (separate issue), thoroughly cleaned the lenses, spent countless hours tuning trying to maximize sensitivity and keep the background low. All the other elements are fine. evening attempted calibrating and analyzing in cool plasma (~ 600 W) versus HOT (1600W). We also have a 7900 series we are planning to swap over to soon and not seeing the same issues. Where could the silver be coming from.

  • Perhaps this tool will help:  https://www.agilent.com/cs/tools/misc/high_background.pdf 

     

    I realize the tool was written for later generation instruments but should mostly be applicable to the 7500.  Some of these items are addressed in the tool, but I would recommend monitoring the Ag counts under the following conditions to see if you can isolate the source:

    • self aspirate using only the nebulizer's tubing, thus removing the peri-pump tubing and autosampler probe if applicable
    • scan for Ag without aspirating (carrier gas = 0 and peri-pump = 0) to see if perhaps Ag is discharging from somewhere beyond the sample introduction
    • check the peak shape for Ag or a close mass while aspirating a standard (preferably single element standard)
    • aspirate the Agilent provided wash solution to rule out any contamination in your sample prep.  Since you mentioned that you don't have the background with your 7900, I presume that your sample prep is not the issue and this won't be very helpful.
    • Try a different sample introduction kit if you have one.

     

    In my experience, older instruments can have elusive and unusual problems.  Hope this helps.

  • Hello!

     

    I had this issue once in an ICP-OES and what had happened in our case was the analyst had accidentally used HCl for the rinse solution instead of HNO3. Caused HUGE Ag issues. Could be something as simple as this, possibly? 

  •   When troubleshooting a high background issue on a particular element the first step is to isolate the sample introduction area from the torch. To do this unclamp the ball joint on the spray chamber and re-clamp it with a square of parafilm. Loosen the spray chamber cap to prevent it from becoming pressurized. Re-light the plasma and then observe the background level of the element in question. At this point the problem either remains or is effectively gone. If it remains it is a Cone/Lens issue. If it is gone it is a sample uptake problem.

       In my experience the uptake side of the system is nearly always the source of the problem. In many cases the ISTD supply has been the cause. Why does this happen? ISTD tubing is often forgotten during the routine replacement of peripump tubing. As long as the ISTD values are stable it is easy to forget that the tubing stretches and ages just like the sample tubing. When the peripump program does a fast uptake, there is a possibility that the CALs STDs can overwhelm the ISTD line and backwards aspirate down the line tainting both the ISTD tubing as well as the ISTD STD itself. Game over!

      The lesson here is to replace ISTD peripump tubing and check its tension frequently to avoid the problem altogether

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