Bioequivalence and Bioavailability Forum

Dear Raghavendra,

For LC-MS/MS methods the choice of IS is usually, in order of preference:
1. stable isotope labelled analyte
2. structural analogue (for instance in your case, azithromycin could have been an option)
3. any other compound which you expect will have the same behaviour as your analyte during sample preparation, HPLC, ionisation, detection etc.

You opted for option 3. So what made you expect that it would have the same behaviour as your analyte ? I'm afraid I fail to see the rationale when looking at the respective structures of clarithromycin and alprazolam.

Regards
Ohlbe