LCMS Standard Addition in matrix

[anastasia.edsell]

I have been working with food matrices for a while using LCMS to quantify targeted pesticides and contaminants. For confirmations we regularly use standard addition (with only 1 level due to needing to save time).

My information has always been that it is recommended to add to the sample at least 2x what the initial concentration approximation is. Can anyone explain to me why this is and how/when it works better than adding the same amount as is seen in the sample?

They do not do the same in GC, is there a reason for this?

[russellb73]

I agree with 2 to 3 x for a couple of reasons

• Major reason (my opinion): Imagine a peak you are going to confirm is analyte "A". If you spike 50/50 or 1x it will be harder to distinguish if there is an unresolved very closely eluting compound. If you use 2x or 3x I believe probably easier to see a shoulder, split peak, see the other compound.
  
  Minor reason: You can tell where compound "A" is and if there is a different compound it will be the shorter peak