How does reference-standard error propagate into a liraglutide content figure?

I have the report as a PDF with the chromatogram on page two, so I can quote specifics.

I would like the arithmetic checked rather than the conclusion asserted.

I have deliberately not used an online calculator because I want to be able to check the result.

Can someone show the working rather than just the answer?

The relevant detail is that start from the certificate on the standard itself, because that tells you the uncertainty in every result that uses that standard.

Purity of the standard is not the same as traceability of the standard — purity tells you the composition, traceability tells you the standard came from a credible source.

Mechanically, comparing your quantitation result to a standard certificate requires that the sample purity be accounted for — if you measure a 95 per cent pure sample against a 99 per cent pure standard, the content result is biased.

The pharmacopoeial standards specify system suitability requirements for quantitative methods that include replicate injection agreement and that agreement should be tighter than two per cent.

Ask for the standard's purity when you buy it.

The underlying point is that most research work uses in-house standards of unknown provenance, which is exactly the situation where a mistake in the standard produces systematic error in every sample measured against it.

The single highest-value check is verifying that the standard's certificate specifies its purity and gives a traceable source.

Storing a standard in a freezer is better than storing it at room temperature, but how much better depends on the chemical stability of the standard.

Certified reference materials are available from national metrology institutes and carry full documentation of their purity and traceability.

The caveat is that a standard certificate is only as good as the issuing laboratory is reliable, and not all certificates are equally credible.

The practical summary: use a standard of declared purity and verified traceability, and check that the certificate is current.

edited 4 Nov 2024 by kwn_analytical — clarified the distinction between purity and content

A standard should be stored as carefully as the samples you test it against, because a degraded standard skews all of your results in a consistent direction.

System suitability for a standard includes that replicate measurements of the same standard give consistent results, and if they do not, something in the method or the instrument is wrong.

One qualification: using a standard from a reputable source and checking its purity on receipt is worth the effort.

Do not use an in-house standard without independent verification of its purity.

Certified reference materials from national metrology institutes carry a purity statement and a statement of traceability, and both matter.

Blank injections using only the mobile phase should give a clean baseline, and any peak in the blank is a contaminant that will affect your sample result.

The pharmacopoeial standards specify system suitability requirements for quantitative methods that include replicate injection agreement and that agreement should be tighter than two per cent.

Ask for the standard's purity when you buy it.