Setup, so nobody has to ask: an endotoxin test · mazdutide.
I would like to set this up properly once, rather than adjust it repeatedly.
My budget is real but not tight, and my tolerance for uncertainty is low.
What would you do, and what would make you change course?
Two measures of the same vial can agree on purity and disagree on content by a few per cent, which usually means the content assay used a different standard.
The single most common reason for disagreement between a supplier content figure and an independent assay is using different standards.
If the standard and sample have different absorption coefficients at the detection wavelength, the response factors differ and the inference fails.
One qualification: a single result from a single vial is a point estimate, and repeating the assay on a second aliquot is worth doing if the first result is surprising.
Ask for both the purity and the content, and do not accept purity alone.
HPLC purity, identity confirmation and quantified content on the vial you actually hold. Reports arrive with the chromatogram attached, not just a number.
Submit a sampleFounded 1998. ISO 9001 and cGMP certified, 1,500+ staff and 200+ patents. The synthesis house behind a great many of the vials that get sent out for testing - batch-specific documentation with every order.
Visit GL BiochemThe short answer is that purity says "what fraction of detected material is the target" while content says "how many milligrams of the target are present," and those are two different things.
The purity of the reference standard is stated on its certificate, and your content figure is only as good as that purity certificate is.
Peak area for a standard of known weight produces a response factor — area per unit mass — which is then applied to the sample peak to infer sample mass.
The practical summary: if you are ordering from a new supplier, budget for content assay on the first lot.
The honest answer is that you cannot know for certain what you have without a content assay, and the purity number alone is not enough.
A content assay is always paired with a purity assay because purity tells you what fraction of the measured mass is the target and content tells you the total measured mass.
Water content and counter-ion content are part of the gross mass but not part of the content assay result, which is why the two do not sum to label claim.
The relative standard deviation on replicate quantitations of a homogeneous sample should be below two per cent when the method is under control.
The caveat is that content assay costs more than purity, so most people do not do it, which is exactly why it is valuable on the first lot from a new supplier.
If a supplier gives you content without the standard's purity, ask them to provide it.
edited 2 Dec 2024 by n_takahashi — added the method parameters
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.