sepcificity and LOQ
Posted: Tue Mar 24, 2009 4:12 pm
by VJ
1) What is the difference between forced degradatin and specificity?
2) Is LOQ istrument dependent (is LOQ different on each instument even instument manufacturer model # is same) ?
Posted: Tue Mar 24, 2009 5:42 pm
by pkenny
1) Forced degradation is stressing the sample in order to create likely degradation products. Forced deg is typically performed by stressing with acid, base, heat, oxidation (H2O2), humidity and light - with a goal of 10-20% degradation from each.
From the ICH guidline: "Specificity is the ability to assess unequivocally the analyte in the presence of components which may be expected to be present." (Basically - does anything co-elute with the peaks of interest?)
Forced deg is useful in order to help determine specificity by showing separation of the main peak from potential degradation products.
2) In my opinion the LOQ could differ instrument to instrument, even with the same model numbers. LOQ is typically determined as 10X the signal to noise. Depending on the system the noise can be very different due to lamp life, quality of mobile phase components, instrument environment. It is common to have a LOQ solution as part of the system suitability of a method so that LOQ is verified prior to analyzing samples.