Doubly charge in High Zn matrix

In our current application in the ICP-MS 7900, we are analyzing zinc electrolyte solutions which contain various levels of Ge.

We run this application 24/4 with samples coming to us every 4 hours, about 100 samples every 24 hours.

We are only interested in the following elements  As, Cd,Co,Cu,Fe,Ga,Ge,Ni,Pb,Sb,Se,Sn,Te, and Tl.

We see a constant increase in our double charge as expected because our samples are high in Zn and various levels of Ge.

I know that Agilent recommends <2%  for doubly charge; we have seen this going up over time without affecting our QC (over 100%).


Is there a way that we can look at doubly charge from other mases that doesn’t require isotope 70? How high is too bad?

I think our system will have a higher than normal residual mass 70 as our matrix is very high Zn.

What study can you recommend for us to see how much doubly charge can we tolerate?

At which point our system have seen so much Zn that we need to look at replacing the octople?

For 24/7 applications, how often do you recommend to be tunning? We have a day/night shift on 4x4 rotation, and the current practice is to tune at the beginning of the shift.

Thanks for any help that can be provided

  • What is the sample matrix?  If you have HCl into your solution that is normal to see a boost in the doubly charge.  This won't affect too much you're reading. Normally we recommend less than 3% without HCl.   

  • Hi Thank you for the answer and help. We don't use HCL in our samples but our Tune 2 does have 3% HCL. I don’t think it is related to the double charge, but we just started to experience issues with the ISTD; see the picture below, only with Tb on both modes (He and H2). We don't see that issue with all the other samples (higher in concentration). I asked the technician to add them to the end of the run to see if there was any improvement, and as you can see, the ISTD recovery jumped again to over 130%, I am noticing a much lower Tl in our QC as Tb is used for Tl 205. Any thoughts? Suggestion?

    Thanks for the help

  • Hi dear JJM,

    Ge has an isotope of 70, so this mean when you are constantly analyzing this element, some residue is on system, e.g. the cones, lenses and some counts are flowing to your ICPMS and for this reason you are seeing an increase on the 70/140 ratio, above 2%. 

    I would not worry about this case. The increase you see on the double charged is coming from your sample and not due to a plasma defect.

    If your QCs are Ok, just continue measuring.

    When you need to clean your system for a maintanance, re-verify the double charged ratio.

    Hope I helped,


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