About internal standard

[jameslizh]

I have a general question: for clinical samples measured by LC/MS/MS, it is required to have internal standard? Thanks for any input.

[tom jupille]

As far as I know, internal standards are not required so long as you can demonstrate acceptable accuracy and precision when you validate the method.

[JGK]

http://www.fda.gov/downloads/Drugs/Guid ... 070107.pdf

The FDA guidance for industry does not mention the use of IS in assays at all. However, in my experience (20+ years), I have not seen a bioanalytical method for an API that has not been an IS method .

Tom is quite correct in saying that if you can demonstrate acceptable acuracy and precision you don't have to use an IS. However, given the low levels being analyzed and the often complicated extraction procedures associated in exracting the APIs from a biological matrix, an IS method is advisable.