7800 internal standard ratio keep going up

I am very frustrated about the ISTD recovery ratio keeps going up, I run total around 150 animal tissue samples, I treated samples so matrix all match, but after 70 samples the ISTD keeps going up to 120% and data shows abnormal from ref QC. Machine performance good, Tune good, everything looks good at beginning but all of sudden it goes crazy. Could you give me some idea what is going on? Sometime it it goes down to 75%. Thank you. 

Parents Reply
  • The easiest way to tell is to determine if there are extreme matrix effects when running a sample. This is often seen with significant enhancement or suppression of the I.S on samples but not during calibration or on check samples like QC. When there are too many ions introduced you experience plasma loading (too many ions so poor ionization) and space charge effects (too many positive charges crowded together during focusing).

    That or if you experience significant downwards drift during an analysis as this is indicative there is too much buildup occurring in the sample intro. This occurs on the nebulizer and cones as they become more clogged with buildup so sensitivity decreases.

    HMI is designed to improve plasma robustness for higher matrix samples so choosing the proper settings for a sample matrix is important to achieve stability. 

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