Why I'm getting the error massage ' CPS RSD value = 7.45 is over the allowed maximum = 5.00' and how does it affect?

Hi,

I'm using Agilent 7700x ICP-MS and analyzed samples containing Cu, Zn, Cd and Gd below 50 ppb. I used standards from 5 - 200 ppb for the calibration curve. For each standard and unknown sample, I've got an error message that CPS RSD is over the allowed maximum = 5.00.

eg: 63 Cu  [ No Gas ] :  CPS RSD value = 7.45 is over the allowed maximum = 5.00

Can someone please give me an answer?

  • Hi  welcome to the Community!  I moved your question to the Atomic Spectroscopy Forum for better visibility.

    Thanks,

    Kristen

  • HI,

    You get the error message because the "standard' three readings of the signal have an RSD value of 7.45. In the masshunter software a maximum allowed RSD of 5 is suggested.

    You can change this in the software and make it higher. However the RSD of 7.45 is an indication that the three readings can have 1 outlier. You should check the three readings and possibly remove the outlier value. You can also edit the method to do more than 3 readings per measurement (e.g 5 or more). This way it is more easy to spot a real outlier.

    You can also try to change the integration time for the problematic elements. When you make this longer it is possible to lower the RSD's in some cases.

    If your CPS of the samples (63 Cu) are very low (<1000) it is more likely that the RSD value becomes a little bit higher than 5.

    An RSD value of 7.45 is not that bad overall.

  • Thank you so much for your answer!..

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