High RSD

I trying to measure 56Fe, I am using Helium mode, and MS/MS scan type. using 5 replicas I am using a 8800 QQQ ICP-MS instrument. The RSD of the Performance report and the Autotune are below 3%. However when I am reading my samples for most of them, the RDS uses to be so high, for example 40 or 60%. If I read those samples again,  usually the RDS goes down. 

Please, could you help me to know what could be happening?

  • Hi,

    i would help, if you could make more detailed statements about you RSDs.

    Is it possible, the always the first replicate is to low (which could be an uptake issue)?

    Or is the first always to high (contamination from rinse solution e.g.)

    Are your sample counts quite low? 

    What is your stabilization time for the Helium Mode?

    Have you tried another Gas Mode (56 is highly interferred by ArO). Hydrogen should give better results in lower levels of Iron.

    Best Regars

    Chris

  • Is it possible that the pre-emptive wash time is to long???

  • Hi,

    There is not a patron, sometimes the first replica has the highest value, sometimes is the middle, and sometimes is the final.

    When I check the CPS file the RSDs are always bellow 5% and the CPS use to be higher than 20,000, the problem with the RSDs comes when I check the concentration (ug/mL).

    The stabilization time for the Helium Mode is setting in 10 seconds.

    I only have tried No gas and Helium mode.

    These are some settings that I am using:

    Plasma robustness: Low matrix

    Preset method: EPA 6020

    Acq Mode: Spectrum

    Q2 Peak Pattern: 3 points

    Sweeps/Replicate: 10

    P/A factor adjustment: On

    Resolution: Narrow Peak

    Scan Type: MS/MS

    Thank you for your help!

    Kindly,

    Catalina A.

  • Hi,

    The pre-emptive wash is off. Should it be on?

    Thank you for your help.

    Kindly,

    Catalina A.

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