Five things a purity figure cannot tell you
An orthogonal method separates on a different physical principle, so that species co-eluting in the first are likely to resolve in the second. Two runs of the same method at…
Laboratory Notebook
Page 7 of 12 of this archive, newest first.
Page 7
A spectrum is a photograph of an ion, not of a molecule
The two ionisation techniques in general use produce different charge distributions, different adducts and different failure modes. Certificates almost never say which was…
Deamidation, oxidation, and the two shifts worth memorising
What would be needed to catch each of these, and what it would cost.
Why Janoshik may run electrospray where another laboratory runs MALDI
The two ionisation techniques in general use produce different charge distributions, different adducts and different failure modes. Certificates almost never say which was…
A few hundred participants carry the whole body-composition argument
A substudy powered to describe a mean is not a substudy powered to detect a clinically meaningful individual change.
Before anything is weighed, the peptide has to be charged
A brief and unromantic tour of the interface between a liquid sample and a vacuum.
Five lines that would change what a certificate is worth
A reader holding a certificate can work out what it does not cover in about ninety seconds, and that is a useful ninety seconds.
Bacteriostatic water, sterile water, and the 0.9 per cent that makes the difference
Every degradation pathway accelerates by orders of magnitude on reconstitution, because the solvent that lyophilisation removed is the reagent most of them need.
What the outcome trials measured in the kidney
Asymptomatic pancreatic enzyme elevation is common on treatment and is not pancreatitis. The distinction is clinical, not biochemical.
Resolution, tailing, repeatability: the arithmetic before the result
System suitability is the set of checks demonstrating that the instrument and method were performing adequately when your sample was injected. It is recorded as a matter of…
Why the compendial sterility test is a rejection test and nothing more
The compendial sterility test cannot demonstrate that a batch is sterile. It can only fail a batch that is grossly contaminated. Everything else is process validation.
The last mile is the warmest mile
The honest finding is more nuanced than the alarm: a lyophilised cake tolerates a brief warm excursion far better than a reconstituted solution does, and the trade’s real…
At 214 nanometres you see every peptide bond. At 280 you see three residues.
Area per cent silently assumes that every species in the sample absorbs as strongly per unit mass as the parent. For peptide impurities that assumption is usually wrong, and…
The change that weighs nothing at all
Deamidation adds 0.98 daltons. On a low-resolution instrument at incretin molecular weights, that is inside the noise.
The arithmetic behind every identity confirmation, worked in full
A peptide has a monoisotopic mass and an average mass, they differ by several daltons at this molecular size, and a certificate that does not say which it quotes cannot be…
The arithmetic behind every identity confirmation, worked in full
A peptide has a monoisotopic mass and an average mass, they differ by several daltons at this molecular size, and a certificate that does not say which it quotes cannot be…
The specification sheet says 500,000. The report says conforms.
Every instrument specification quoted in an advertisement is a best case obtained on a calibration mixture, not on a submitted vial.
HbA1c and its lag: what a result three months old is telling you
What the SURPASS and STEP programmes reported, with the estimands and the baseline values stated.
Errors ranked by how much dose they move
A pharmacist catches most of these in licensed practice. In this market there is no pharmacist, so the checks have to be structural.
A reference interval is not a target, and a result outside one is not a diagnosis
The arithmetic of the reference change value, worked for the analytes that matter here.