Duplicate standards

[Confused gasman]

How do people interpet the USP suitability requirements on standard RSD's? Do you say that the 5/6 minimum standard injections must come from one standard preparation, or do you use response factors from two standard preparations? ~(I run duplicate standards all the way through the run)
Cheers
Confused Gasman

[krickos]

Hi

hmmm well USP <621> states "replicate injections of a standard.." for me that is one solution and typically a RSD based on area unless the individual monograph states something else.

However USP do not define RSD in the same way (no definition in <621> at least as I recall, perhaps elsewhere?) as Ph Eur (2.2.46): "....individual values expressed as peak area, peak height, or ratio of areas by the internal standardisation method...."

So I would nor recommend responsefactors unless the individual monograph states so.
As you surely know, reproducibility of responsefactors and RSD of replicate injection based on area/height covers different parts of the analytical chain.

[cjwitt]

USP does state "replicate" standard injections to establish suitability as well as bracketing standard use (at the end of USP <621>) The RSD requirements are different for HPLC and GC and it is based on what %RSD is chosen.

HPLC- If the RSD is less than 2, then use 5 injections, and if the RSD is greater than 2, use 6 injections.

GC- Same requirements, just using an RSD of 15% instead of 2%

The standard injections all come from the same standard preparation unless the USP monograph specifically states different.

[jane bench]

Our practice is to have 5 replicates for standard 1 and then just one replicate of standard 2. All that before injecting samples. So, we have two independent standards (always).Then we check out for RSD value of five replicates of standard 1 . For assay tests RSD must be less then 2%, and for residual solvent analysis less then 15%.

[Consumer Products Guy]

The RSD requirements are different for HPLC and GC and it is based on what %RSD is chosen.

HPLC- If the RSD is less than 2, then use 5 injections, and if the RSD is greater than 2, use 6 injections.

GC- Same requirements, just using an RSD of 15% instead of 2%.

We've been using the HPLC guidelines above for both HPLC and GC, stated in our SOP. Right mow, the only cGMP GC assay we do is for alcohol, and we follow <USP 611> which allows RSD < 4 so that's what we use there (but our RSD is way less, less than 2%). I'll need to check on the typical USP GC requirements.