I am trying to validate an LCMS instrument with clinical drugs.
When most of my analytes look good, I have a about 8 drugs which does not pass the validation for lower calibrators if I use the corresponding IS.....but they seem to pass if I use an IS from another group of analytes. For example, for cotinine when I use the nicotine IS, the lower calibrators are not passing but if I use 6-MAM-D3 they seem to pass. Similarly, for Methylphenidate, when I use Ritanalic acid IS, lower calibrators do not pass but when I use Desipramine IS they pass.
Any thoughts on this....any recommendations how to correct.
It depends on the way, how you loose sample mass. If loss is during sample pre-treatment, similar chemical behavior in the sample preparation procedure is a must. If you use internal standard component just to learn. what is the volume of injected sample, any component with known concentration will do (or you can even average values, calculated for different components with known concentration).
Hi Chitra,
There are multiple things you might need to investigate here.
1) Are the area counts of your heavy labeled IS (Nicotine in this case) constant throughout the batch (
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