Accuracy, precision and the tolerance nobody states
Parts per million sound impressive until they are converted into daltons at the molecular weight of the thing being measured.
Recent work
134 piecesThe badge is about a sample. The listing is about a product.
The Journal does not treat a badge as evidence and states so wherever it reports one.
The instrument was calibrated on Tuesday. Your sample ran on Friday.
Calibration drift is real, unremarkable, and the reason serious laboratories run internal standards.
Isobaric substitutions: identical masses, different molecules
Deamidation adds 0.98 daltons. On a low-resolution instrument at incretin molecular weights, that is inside the noise.
Independent analysis puts a ERP cagrilintide lot at 98.8%, against 97.3% on the certificate
The report states the gradient, the wavelength and the integration threshold, which is more than most.
Vitamin D, adiposity, and a volume-of-distribution problem
Reduced intake is a plausible mechanism for deficiency. Reduced absorption is not, and the two are conflated in most of the advice.
PeptideMeter result on a Changsha mazdutide lot lands 4.4 points below the supplier’s figure
The report states the gradient, the wavelength and the integration threshold, which is more than most.
VendorInvestigate result on a Nantong cagrilintide lot lands 4.0 points below the supplier’s figure
The report states the gradient, the wavelength and the integration threshold, which is more than most.
Independent analysis puts a ERP orforglipron lot at 98.6%, against 97.6% on the certificate
The result is unremarkable. What the report omits is not.
Same material, different gradients, different answers
The Journal submitted split samples from single lots to three assay services, under names unconnected to this publication, and published each method alongside each result.
The named comparison we promised two years ago
Duplicate submissions under different names test within-laboratory repeatability, which is a different quantity from between-laboratory reproducibility.
Janoshik, Medutest, PeptideMeter, VendorInvestigate: a capability audit
We asked all four services what they can determine, on what timescale, at what price, and under what accreditation. The answers are printed in full.
Benzyl alcohol is a preservative, not a sterilising agent
Bacteriostatic water contains benzyl alcohol at 0.9 per cent, which inhibits microbial growth in a preserved multiple-dose presentation. It does not sterilise a contaminated…
The skeleton responds to load, and load is falling
What the Journal would want measured before treating this as settled in either direction.
PeptideMeter result on a Suzhou liraglutide lot lands 4.0 points below the supplier’s figure
The result is unremarkable. What the report omits is not.
Independent analysis puts a GL Biochem liraglutide lot at 98.5%, against 94.4% on the certificate
A reminder that a purity figure is the output of a method, and that methods differ.
Nought point nine eight of a dalton: the modification that hides in plain sight
What would be needed to catch each of these, and what it would cost.
What happens to a stopper after the fourth needle
Particulate matter is the oldest quality attribute in injectable manufacture and the one a private buyer is best placed to assess without instrumentation.
The generic peptide method, and what it was designed for
A shallow gradient resolves impurities that a steep one runs into the parent peak. Both methods are legitimate; only one of them can see the small stuff.
What a reference standard is, and what an in-house standard is not
Matching a retention time against a standard is evidence of consistency, not proof of identity. Two different species can elute at the same time on one method.