Chain of custody, and where it begins
What a laboratory can and cannot know about the provenance, storage history and representativeness of what lands on its bench.
PeptideMeter
Page 5 of 8 of this archive, newest first.
Three services, one lot, and a spread of two and a half points
Duplicate submissions under different names test within-laboratory repeatability, which is a different quantity from between-laboratory reproducibility.
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…
Reproducibility, measured rather than assumed
Duplicate submissions under different names test within-laboratory repeatability, which is a different quantity from between-laboratory reproducibility.
Six words a verification badge would need to mean anything
What a verification mark would have to carry to be checkable: a date, a lot, a method, a submitter and a link to the report.
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.
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…
Reproducibility, measured rather than assumed
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.
Why a result on one vial says less than the trade needs it to
A result on one vial generalises to a batch only if the vial was drawn in a way that makes it representative — and nobody records how it was drawn.
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…
Counter-ion, water, salt: three masses with no chromatogram
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…
Why a result on one vial says less than the trade needs it to
What a laboratory can and cannot know about the provenance, storage history and representativeness of what lands on its bench.
Sending the same vial twice, under two names
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 badge economy, and what it is actually certifying
What a verification mark would have to carry to be checkable: a date, a lot, a method, a submitter and a link to the report.
We split six vials four ways and posted them
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.
What a split-sample exercise can establish, and what it cannot
Two years ago we ran an anonymised version of this comparison and promised a named one. This is it, with every method printed in full.
Disregard limits: what a regulated laboratory does with a tiny peak
Chromatographic software does not integrate every fluctuation in the baseline. It applies a threshold, and the threshold changes the reported purity by amounts that matter…
Why a result on one vial says less than the trade needs it to
A result on one vial generalises to a batch only if the vial was drawn in a way that makes it representative — and nobody records how it was drawn.
Reproducibility, measured rather than assumed
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 conservative convention: report the lower of two numbers
Aggregates dissociate in the mobile phase and are recorded as monomer. Only a size-based separation reports them.