I am trying to view Ca at roughly 1ppb in brine samples on a 7900 using UHMI and Ca40 in H2 mode. Does anyone have experience with this?

I am seeing roughly 20ppb in "clean" samples that should have less than 1ppb Ca in them.  Is there a correction equation for removing interferences (possibly from the high Na content) or some tuning parameters that could be changed to try to accurately report these values?  Thanks for any and all advice on this!

  • Hi Paul, as I understand your brine samples have a lot of Na content and for this reason your are running the Plasma Condition as uHMI, so this means a lot of Argon dilution before your sample reaches the plasma region. This is definitely a good choice as without uHMI your cone/lens system will be very fast covered from your Na content, resulting on extreme drift. As you understand Ca 40 has a known interference from Ar-40 and of course there is plenty of Argon in your system from your plasma. H2 Mode is the best choise as H2 neutralizes the Ar(40)+ interference and leaves the Ca signal almost unaffected. But to be honest it is really difficult to remove 100.0% of the Ar-40 interference and for this reason I would expect a slightly increasing BEC on the Ca-40 calibration. I suppose is close to 20ppb. Can you check please your Ca-40 calibration and the DL and BEC values? That is the limit of your method you cannot report / measure lower concentrations than your BEC. To be honest 20ppb Detection Limit for Ca is a very nice DL, especially in uHMI mode.

    Hope this helped,

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