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ICPMS 7900 ISTD recovery bounces

bastacy

I have been having an issue on my 7900 ICPMS where my ISTD recovery will increase or decrease on one sample. It seems to be random and doesn't always fall outside the recovery lines, but sometime will. It is very frustrating when it happens on a calibration point or check standard. We have replaced and cleaned most everything we can (Nebulizer, tubing and lines for autosampler and peripump, ISIS valve head, etc). This issue doesn't occur on our 7800 so I don't believe its something in our samples/standards. It happens sometimes in NoGas mode and other times in He mode. The photos included outline a few instances of it happening. I'm not sure where to look next. I browsed the forum and only saw one thing similar but it was only happening in He mode for them. If anyone has seen this before or has any suggestions, feel free to give them!

Thank you!

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  • 0

    The reason for this from what I can tell are the RSDs. When the I.S. RSDs are poor, you will see it increase or decrease randomly.I have some questions to try and figure out the culprit for the RSD issue.
    Are you using online internal standard addition? Do you have an ISIS valve? What is the acid matrix of your samples and I.S? Are your samples high %TDS? Are you using third party peripump tubing? 

  • 0 in reply to Chelsea Tajc

    We are not using online internal standard addition. 
    We do have an ISIS valve.

    Matrix is 1% HNO3 for standards, samples, and I.S.

    Samples are mostly purified drinking water, so TDS is not very high.

    Peripump tubing is CPI.

  • 0 in reply to bastacy

    Hello, 

    Just to make sure, you are adding I.S to every sample and every standard during prep and not using the peripump to deliver I.S? So the peripump is only being used for carrier and waste correct?

    Are the RSDs for the analytes also high when the I.S RSD is elevated? If I.S is in each solution I would expect the analyte RSDs to also bounce high as well since it's all one solution.

    Can you screenshot your ISIS/Peripump settings in your method and share them? If the ISIS pump is set too fast you might get cavitation happening which causes small air bubble formation and can cause RSD issues.

    Also, what size i.d. ISIS loop are you using? Is the i.d the same outer diameter as the autosampler probe line or is it larger and the same size as the ISIS waste line?

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  • 0 in reply to bastacy

    Hello, 

    Just to make sure, you are adding I.S to every sample and every standard during prep and not using the peripump to deliver I.S? So the peripump is only being used for carrier and waste correct?

    Are the RSDs for the analytes also high when the I.S RSD is elevated? If I.S is in each solution I would expect the analyte RSDs to also bounce high as well since it's all one solution.

    Can you screenshot your ISIS/Peripump settings in your method and share them? If the ISIS pump is set too fast you might get cavitation happening which causes small air bubble formation and can cause RSD issues.

    Also, what size i.d. ISIS loop are you using? Is the i.d the same outer diameter as the autosampler probe line or is it larger and the same size as the ISIS waste line?

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