ICP-MS7900 Accuracy Issues

Hi, we are running samples on our ICP-MS7900 to determine zinc content of samples. Recently we have had issues with some samples coming back with low results (have cross references with another machine, and the sample is not the issue). However, some samples come back fine, whilst others are low, even within the same batch. We have performed maintenance, but are wondering whether there is anything else we could try to improve the accuracy of our machines results?


  • Hi

    What maintenance performed..can you share detail....

  • We did out weekly glassware change/clean and replaced tubing. Have also just cleaned the cones and lenses.

  • Hello ,

    Zinc suffers a lot from contamination. From my experience, sometimes the following occur:

    1) Memory effects - is the rinsing time between the samples enough to clean out remaining Zn from samples in the batch? To check this, you can introduce some blank solutions as BlkVrfy between the samples so you can get a better look.

    2) Check the standards - Zn standard may be contaminated (with more Zn than it should), reflecting in the determination of your samples. Do you have another Zn standard to run as a sample to check the accuracy, or a CRM? Besides, are you using a multielemental standard or are you mixing monoelemental standards to come to a final intermediary multielemental standard? If so, you should check each standard to see if Zn is coming from any monoelemental standard.

    3) Have you tried running the same sample multiple times, and see the RSD between the final reads? This should give you some insight over sample/instrument stability.

    4) Are you running other elements in the same batch? Does the problem occur with other elements?

    5) Have you tried other Zn isotopes? I know they may be not as sensible as the m/z 66, but it is worth the try.

    Hope this helps,

  • Hi Rodolfo,

    Thanks for above suggestion. In my case, I suffer bad zinc linearity for my multielemental std. my std scale is from 0.2ppb to 10 ppb. With more than 10 times injection of each std, my 0.2 and 0.5 std was lower( calibrated as 0.15, 0.43 average). But other elements in the same batch are ok. 

    Also the RSD of each injection is not stable. Sometimes within 5%, sometimes is above, can be 9%. The RSE of the calibration curve is high(19%). I check the intensity of our lowest std 0.2 ppb is five times higher than  blk, so I assume the sensitivity should be enough for calculation?

    Do you know in this case how can I improve the RSE and linearity of the calibration curve?

    Thanks very much.

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