What is the typical ISTD Recovery Outlier Setting Range and what do you do when the ISTD is outside that range for one of your samples?

We have currently set the ISTD Recovery % range to 80% to 120% on our ICP-MS.  For some of our samples this range is exceeded.  Should we dilute the sample and rerun it?  Can we switch the ISTD to another that is within our 80% to 120% range, but maybe has an ionization potential that isn't as well matched?  Can we use a wider ISTD Recovery range?  What is the standard practice for this situation?

  • Hi,

     

    If the recovery of the ISTD is exceeded the 80-120% limit you apply the best approach is to dilute the sample and re-measure. To choose another ISTD element isn't the best way, the element of interest is always coupled with the ISTD element what has the same behavior with spectral and physical interferences.

     

    However maybe a recovery of 70-130% of the ISTD and a good combination/choice of ISTD could give acceptable recoveries of the sample. This could be only proven by investigation/validation.

     

    One note, most of the time the ISTD recovery is exceeded the limits due to the Total Dissolved Solids load. Only a more robust setup of the plasma like HMI or diluting the samples can beat this.

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