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.
PeptideMeter
Page 2 of 8 of this archive, newest first.
Chain of custody, and where it begins
Chain of custody, in a regulated setting, begins at sampling. Here it begins when the package arrives.
An interlaboratory comparison nobody had run
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.
Counter-ion, water, salt: three masses with no chromatogram
Aggregates dissociate in the mobile phase and are recorded as monomer. Only a size-based separation reports them.
The badge is about a sample. The listing is about a product.
A badge asserts that something was tested. It does not assert what, when, on whose sample, by what method, or whether the lot on sale is the lot that was tested.
A percentage is not a specification
This piece takes the measurement apart into the decisions it is made of, because each decision moves the answer.
Why a result on one vial says less than the trade needs it to
The condition on arrival is recorded by some services and not others, and it is one of the more informative lines in a report.
The badge economy, and what it is actually certifying
A badge asserts that something was tested. It does not assert what, when, on whose sample, by what method, or whether the lot on sale is the lot that was tested.
Reproducibility, measured rather than assumed
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.
Five things a purity figure cannot tell you
A chromatogram is silent on everything that does not absorb: counter-ions, water, inorganic salts and non-chromophoric excipients all contribute mass to the vial and nothing…
What a laboratory knows about the material it receives
Every third-party report in this market describes a sample somebody chose to send. That choice is outside the laboratory’s control and outside its records.
Custody, condition and the temperature nobody logged
Chain of custody, in a regulated setting, begins at sampling. Here it begins when the package arrives.
The badge is about a sample. The listing is about a product.
Lot-level verification with a public report is a real and achievable thing. It exists in this market, on a minority of listings.
Counter-ion, water, salt: three masses with no chromatogram
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…
The submitted sample: the weakest link in the whole system
Every third-party report in this market describes a sample somebody chose to send. That choice is outside the laboratory’s control and outside its records.
Custody, condition and the temperature nobody logged
The condition on arrival is recorded by some services and not others, and it is one of the more informative lines in a report.
Baseline construction, and the area that depends on where you draw the line
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…
The badge is about a sample. The listing is about a product.
Every step between the laboratory report and the product page removes information, and the badge is the last step.
The wavelength decides which impurities exist
Peptide bonds absorb strongly near 214 nm; aromatic side chains absorb near 280 nm. A method reading at 280 is blind to any fragment lacking an aromatic residue.
Pore size, particle size, and why peptides need the wide pores
Ion-pairing additives sharpen peptide peaks and suppress ionisation in the mass spectrometer, which is why the purity method and the identity method are often not the same…