By Anonymous on Friday, October 11, 2002 - 01:36 pm:
Someone uses standard deviation of signal at zero concentration to calculate LOD and LOQ. The thing is that one only has a set of linearity data at 80-120% of target sample concentration level. How can you get a standard deviation of signal at zero concentration from this data?
By chris on Friday, October 11, 2002 - 01:49 pm:
Note the following from the USP "Analytical methods for quantitation of major components of bulk drug substances
or active ingredients (including preservatives) in finished pharmaceutical products." If you are only working with something like this, you should not need to worry about LOD and LOQ (USP , Validation of Compendial Methods).
By Anonymous on Friday, October 11, 2002 - 02:04 pm:
But if you want to establish an impurity assay and you have a set of linearity data at 80-120% of the specification level. How to calculate them? Thanks a lot for the help.
By A.Nonymous on Saturday, October 12, 2002 - 02:32 am:
Check this.
By Anonymous on Monday, October 14, 2002 - 12:40 am:
After having obtained your regression line, you can use the standard deviation of the y-intercept or the residual standard deviation (Excel can give them to you). The calculation can be made regardless of the range, but anyway, if you are working with impurities you should prove linearity between LOQ and 120% of the specification.
By Anonymous on Monday, October 14, 2002 - 09:01 pm:
For Impurity assay you are required to carry out your linearity from LOQ to 120 % as per ICH. So in my opinion if you are carrying it from 80-120 for impurities better you rethink.