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Source of Zn contamination

carwogill

Hi ICP users.

I have a question about a possible (suspected) source of Zn contamination.

I am using a CEM SPD microwave system for sample prep and I am obliged to use a magnetic stirring bar in every quartz microwave vessel. For a long time now I have problems with random high Zn counts. A duplo measurement (separate prep with different vessels and stirring bars) can vary from <0.05 to 10 ppm Zn.

My question is this: can the material of the magnetic stirring bars be responsible for Zn contamination? I never analyse samples with very high Zn content. My quartz vessels are cleaned an checked. It is a mystery to me.

Hope one of you can give me some advice.

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  • 0

    Chelsea gave a great response and I agree about the source possibly being the autosampler vials/tubes- I would just add the following:

    It's unlikely that the Zn contamination is from the stir bars. We tend to see the following elements from stir bar contamination – Al, Cu, Cr, Fe, Ni. This is because the most common type of stir bar that CEM uses/sells are PTFE coated AlNiCo stirring bars. If you aren't seeing Al, Cu, Cr, Fe or Ni also, then it's not likely coming from the stir bars. I would also note that stir bars should be considered as consumables and should be replaced from time to time. 

  • 0 in reply to Tina Harville

    Hi Tina, thanx for your reply!

    me suspecting the stirring bars was a last resort for me Tired face. I did know that these were so-called AlNiCo magnets. But over the years I really don't know what to check anymore. Maybe the source is to be found, like Chelsea suggested, in indoor environment like ceiling, particles from AC. If that is the case maybe 'low-level' Zn analysis is something I simply can not do.

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  • 0 in reply to Tina Harville

    Hi Tina, thanx for your reply!

    me suspecting the stirring bars was a last resort for me Tired face. I did know that these were so-called AlNiCo magnets. But over the years I really don't know what to check anymore. Maybe the source is to be found, like Chelsea suggested, in indoor environment like ceiling, particles from AC. If that is the case maybe 'low-level' Zn analysis is something I simply can not do.

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