Hello every one
I'm trying to quantitate essential amino acids in serum or DBS by Lc-MSMS(Quadrupole ABsciex 4500 ) .
by searching the net for trusted protocol , all protocols that published employ labeled amino acids internal standard (which I don't have) .
please any one can share a trusted FIA- or LC- MSMS protocol that employ external amino acids standards.
thank for any suggestions
Hi Hayder,
The answer depends on what amino acids you are wanting to analyse. As a general method might not be applicable to all amino acids, if you have found methods that meet most of your needs but it is only the internal standard that you are stuck on then that is different.
I would suggest using a method you have found and using a generic internal standard. Labelled IS can be quite expensive but generally are much better as it goes through the same extraction.
Amino acids are generally polar and a couple of generic ISs that I would suggest are gemcitabine (cas number: 122111-03-9) and indomethacin (cas: 53-86-1). These may be a good starting point but they do come with some drawbacks. I would use a concentration around your mid QC level to start and adjust it from there.
You will need to make sure you perform a matrix effect experiment comparing your IS to all your analytes. This will allow you to check that the IS is suitable. A good IS will pass through an extraction in the same way as your analytes of interest. So this step is crucial to ensure that you dont have excessive variability and problems reproducing data.
I hope this helps
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