slope and intercept change

[meillid]

Hi, all,

what does slope and intercept changing means for the calibration curve of a method? (r value is always better than 0.9995)

is a method is regarded validated to used if slope and intercept changes along time or fixed only between the instrument maintenance?

Thanks a lot!

[james little]

in my methods, did note a variation in slope if I ran the sets of standards many times over a 24 hour period.

Never understood the systematic drift.

Finally just made sure I met the criteria set for QC samples in the following document..

http://www.fda.gov/cder/guidance/4252fnl.pdf

seemed like high standard deviations to me, but did turn out to be a realistic goal..