my favorite... lod/loq :)

[n-cute]

Dear All,

Does anyone of You make injections to confirm LOD and LOQ calculations? e.g. 10 injections to calculate accuracy and precision for LOQ looks OK, but what to do with LOD? Theoretically it's lower than limit of quantification. Maybe just some injections to confirm retention time or... what?

[JM]

we have a limit of RSD NMT 30 % for LOD replicate , provided all peaks are "visible".

JM

[n-cute]

Thanks for that, it seems OK to me.
Does anyone of You have different approach to this?

[JBush]

I forgot how useful these forums can be. Guess work has gotten the best of me.

It was suggested to me by a co-worker that you run precision (6injections) at decreasing concentrations and measure the %RSD until the %RSD hits some company set specification. Actually as we speak I am currently running a sequence to try this out. I will use 10%RSD for my LOQ, which is in addition to the standard LOQ = signal to noise of 10. This will make me feel more comfortable in reporting a limit of quantitation of an hplc method to vendors and outside departments.

I can't comment on the %RSD of 30% for LOD since I have not yet seen my results.

Anyway I hope this helps. I don't have any documentation to support this but it could provide useful data if questioned in the future

[Dan]

All,

I have never used a precision requirement for the LOD. The requirements we use are: S/N is not less than 3 and that the LOD must be of a certain level. Usually the level should be about half the concentration of the specification limit/LOQ. So if the specification is 0.1% w/w, then the LOD should be 0.05% w/w (or less).

We do use an RSD requirement of not more than 10% for the LOQ.

Reagrds,
Dan

[ntruong]

Hi n-cute, JM, JBush and Dan,
The ICH guidelines specifies the requirement of signal/noise for LOD is 3 and about 10 for LOQ. What is the point of trying to prove precision and accuracy at the low level? As long as you satisfy the requirement of LOD and LOQ during method validation, you don't need to revisit or prove it again in your routine analysis.

[JM]

ntruong,
Please read ICH guidlines carefully, after estabilishment of LOQ , as per ICH,

"The limit should be subsequently validated by the analysis of a suitable number ofsamples known to be near or prepared at the quantitation limit."

In-otherwords you need to prove precision at LOQ. For LOD the general industry practice is to varify the value ( derived from S/N) by replicate RSD.

During the method transfer to another lab you need to verify the LOD and LOQ values as it changes from system to system.



JM