LOQ

[tonja79]

I at all,
I need Help please.
Someone can send me a detail example how can I calculate the LOQ (limit of quantitation) on the residual standard deviation of the regression line?
Thanks

Tonja

[NJ1979]

Dear Tonya,

Really the LOQ needs to be determined experimentally, and depending on the quality level you are working to, the criteria for this may vary.
Frequently, the LOD (limit of detection) is determined by running a series of dilutions and set at the point where the analyte response is approx. 3 times higher than the level of the baseline (noise). Then generally the LOQ would another 3.3 times greater than this (approx. 10x noise) and tested by whether the level of analyte at this concentration can be accurately and precisely calculated by running at least 3 control samples, spiked with analyte, at this pre designated LOQ.

I hope this helps,

Best regards,

Nick J.

[fmcleod]

Dear Tonja,
The ICH guidelines give the following formula for calculating the LOQ from the calibration curve

LOQ =10 σ/S

S is the slope of the calibration curve.
σ can be calculated 2 ways - the standard deviation of the regression line, or the standard deviation of the intercept. A modern chromatography system (or Excel) will be able to calculate either of these values for you.
Hope this helps.