ICP-MS replicates and RSD

Why is the number of replcates normally set at 3.  Where does 3 come from?  What RSD is normally applied to these 3 replicates and why?

  • Hi GM!

    I think the number of replicates (3) has to do something with statistics. With three measurements you can, most of the time, determine really quick if there is an outlier, which can than be removed.

    More replicates is possible of course, but then the analysis time becomes longer.

    The RSD of the replicates depends on the measured signals. For counts >1000 cps an RSD of 0- 2% is probably common. Counts< 1000 cps can have much larger RSD's.

  • In my world of environmental analysis official methods (e.g. EPA) tend to all require 3 replicates. I'm not sure about other industries but that may also have been part of the genesis of that default, in addition to the usefulness of seeing a trend in the replicates. i.e. rising or falling replicates indicating issues on the stabilization of the signal. 

    Regards, 

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