Bioequivalence and Bioavailability Forum

Dear Rajendra,

❝ How to Select ISTD for bioanalysis.

That's a wide question !
Gold standard in MS methods: stable-isotope labelled IS. That's your analyte, marked with a stable isotope (usually deuterium, possibly ¹⁵N or others, or a combination) at a few positions (usually 3 to 6), wich will result in a different m/z. The main advantage is that it will normally be extracted the same way as your analyte, and suffer from matrix effect the same way (though a few publications mention differential matrix effects). Problem: expensive, and may not be commercially available.
Silver medal: structural analogue. The same compound as your analyte, just with a methyl-, or any such neutral group, added. Will hopefully be extracted the same way as your analyte. Avoid analogues where the different group includes atoms which may influence recovery, polarity or response (such as O, N, S...). Problem: may not be available. May not compensate matrix effect, if eluted at a different retention time.
Last solution: just any substance you may have in your stock of reference substances, that will hopefully be extracted the same way as your analyte, and be detected with the same polarity. Much cheaper, no availability problem, but you may need to test several substances during method development before you find the right one. First try with substances with common chemical properties (acid or base, common structural groups).

❝ What is role of ISTD in Batch Acceptance and how to tackle the istd

❝ Variation.

Please use the search function of the forum ! Have a look at this thread and that thread for previous discussions on this topic.

❝ Why PPG used in calibration of MS/MS.?

Doesn't your MS/MS instrument come with a manual of some sort ? I'm quite sure there is plenty of information in it, for a start

❝ how many subject can be run with one calibarion curve..?

How many samples can you practically prepare in one batch ? I would recommend not to analyse several batches of samples, prepared independently, under a single curve as you may end with problems and questions in the interpretation of the results of QC samples, and acceptance/rejection of the data (have a look at this thread). And how many samples can you analyse in the period of time for which you have demonstrated on-injector stability ?

Regards
Ohlbe