correct choice for fortify. Help Urgent

[bolivar19]

HI,
i´m work in toxicology lab and yesterday i was reading SWGTOX Standard Practices for Method Validation in Forensic Toxicology Laboratories, seems interesting and i hope to help me for validate all methods for pesticides, drug abuse, volatile, etc...

Now we are validating a method for quantification of Benzoic acid by GC/MS in human plasma. my question is:

For lineal calibration model:

we need to fortify a blank plasma for all six levels in the work range? or

we need to fortify a blank plasma extract?

i need to guarantee accuracy and presicion in all levels,

Which is the best way to fortify?

[tom jupille]

If you fortify the extract, you will be measuring the reproducibility of the *chromatographic* part of the process, ignoring any errors from the sample prep.

If you fortify the blank plasma, you will be measuring the reproducibility of the *total* process (sample prep + chromatography).

If this were my project, I would fortify (spike) the blank plasma. If the reproducibility is inadequate, repeat using fortified extract. The difference (if any) will tell you where the dominant source of error lies.

[bolivar19]

Thank you very much. Mr. Tom jullipe
All my team and me are grateful whit you.
You are right. I was.studied and We have a error source owing matrix effect.
Clarke,s Analysis of Drugs and Poisons say's that biological specimens are very complexs matrixs.
UNDOC and SGWTOX sugget fortified extract for linearity test. But for bias, precision and recovery must be fortified blank sample.
Because we have to guarantee accuracy and precision in all calibration levels.thank you.