PREDICTION OF LOD AND LOQ

[kalidassa]

Hai
Which is correct method to predict the LOQ and LOD for the solvents. Our practice is injecting some 10% or 5% of specification concentration level based on the signal to noice ratio of that solution we are back calculating and predicting the LOQ and LOD.

Thank you
KALIDASS

[krickos]

Hi

It seems like you are doing residual solvent analysis in pharmaceuticals so, well the ICH Q2R1 guideline simply states that "low" concentrations should be used.

Having a set % level to work at seems "wrong" from several points in generel but if I limit myself to a typical GC-FID analysis:
Response differences, for instance DMF and toluene have almost identical general limits according to ICH Q3C guideline but if you inject 5-10% of limit of those the response will likely be significantly different.

Also if you use headspace injection you must take into account different partionkoefficeints between gas and liquid phase.

Further, limits of solvents especially the class 2 ones are very different from solvent to solvent, for instance you will not likely detect 5-10% of limits for certain low limit solvents, especially if default pharmacopiea methods is used as base for your analysis.

I would rather recommend that you extrapolate from the linearity test and test a few different concentrations from that extrapolation.