Re: Internal Standards for LCMS
Reply #1 –
If you want to do real quantification then you need an internal standard for each compound you want to measure.
A weaker approach would be external calibration curves with non-labelled standards. This would not take into account the matrix effect. So unless you can validate that this makes some sense with your particular matrix by comparing to an approach with labelled standards first I would not give any validity to such an approach.
For untargeted metabolomics people disagree heavily. Some use a single standard, some try to use a standard for each compound group or possibly group by retention time.
I have yet to see anyone show that internal standards help anything in untargeted studies...
EDIT: I should clarify that my comments regarding untargeted was for the idea that you can use internal standards to quantify in an untargeted setting and the idea that you can use internal standards to correct analytical drifts.
As @stacey.reinke and @romanas chaleckis pointed out they can however be very useful to check the system.