Bioequivalence and Bioavailability Forum

Hi Ladi,

❝   Cal curve, QC are prepared from 480 uL blank plasma and 20 uL spiking solution (in 50% methanol) before extraction.

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❝ – To analyze study sample pipette 480 uL of the study sample and add 20 uL of 50% methanol before extraction.

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❝ The question people are having is should the drug concentration be calculated base on total volume of 480 uL or 500 uL?

I don't think it is a silly question at all. I bet most of us make mistakes and are in doubt very often when we calculate dilutions and concentrations. It is a serious matter. My own chemistry teacher had to take early retirement because she was so perplexed by my persistent miscalculations.


Late correction - I seem to have goofed it up as usual (yeah, big surprise ).

The way I understand you:
You have xyz ng analyte per 20 uL; you then dilute that entire volume to 500 ul before execution. Now your working conc. is 1/25 of the initial concentration.
And you do not have a vial containing anything that is 1/24 of the initial concentration as would be the case if you had to use 480 uL as the final volume.