The figure of merit this trade chose, and the four it did not
A market that competes on one measurement will optimise that measurement. There are legitimate ways to raise a purity figure that involve no change to the product at all.
Mass spectrometry
Page 3 of 6 of this archive, newest first.
One measurement, twenty companies, forty compounds
The Journal has read several hundred certificates from twenty companies. The number is almost always there; the method behind it almost never is.
The instrument was calibrated on Tuesday. Your sample ran on Friday.
Parts per million sound impressive until they are converted into daltons at the molecular weight of the thing being measured.
The impurity hiding underneath the parent peak
Where two methods disagree, the conservative convention is to report the lower figure. It is not universal, and whether a laboratory follows it belongs on the report.
Nought point nine eight of a dalton: the modification that hides in plain sight
Stereochemical inversion changes the molecule, changes its biology, and changes its mass by exactly nothing.
Why purity is the cheapest number to flatter
The Journal has read several hundred certificates from twenty companies. The number is almost always there; the method behind it almost never is.
Mass spectrometry answers a different question, properly
The most useful single addition to any purity determination is a second separation under a different pH or on a different stationary phase, and the second-most useful is a…
Calibrated, qualified, accredited: three words that are not synonyms
An assay against a quantitative reference standard measures how much is present. Area per cent measures what proportion of the visible material is the parent. Only the first…
Where the solvent front ends is a decision, not a fact
Regulated pharmaceutical practice has explicit reporting, identification and qualification thresholds. This trade has none, which is why a purity figure carries no…
Leucine, isoleucine, and a difference no balance can measure
Stereochemical inversion changes the molecule, changes its biology, and changes its mass by exactly nothing.
The conservative convention: report the lower of two numbers
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…
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…
A method is a set of numbers. All of them belong on the certificate.
Column chemistry, particle size and pore diameter determine what the separation is capable of before the gradient is even programmed.
The change that weighs nothing at all
What would be needed to catch each of these, and what it would cost.
A number without a suitability record is a number from an unknown instrument
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…
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.
One measurement, twenty companies, forty compounds
A market that competes on one measurement will optimise that measurement. There are legitimate ways to raise a purity figure that involve no change to the product at all.
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.
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…