Every letter we have printed

The table showing what each method can detect is valuable but incomplete. You show no row for C-terminal truncation or N-terminal truncation as distinct phenomena. These are not rare, and they often elute differently depending on which end is missing. A generic gradient might resolve them; an improperly designed orthogonal method might not. The capability matrix should separate these cases.

You list five things a purity figure cannot tell you and then say the list is not an indictment of the technique. It reads like one. If a measurement is silent on content, aggregation, sequence, isomers and microbiology, why is it the measurement this market uses at all?

Cyclisation at an N-terminal residue produces a mass change of a few daltons and a chromatographic shift, and it is entirely benign to look at. It is the pathway most likely to be integrated as part of the main peak.

Degradation products are not inert and the literature on them is thin for most sequences in this market. A discussion of purity that only counts what is lost, and never asks what it became, is half a discussion.

Retest date and expiry date are different concepts and the trade uses them interchangeably. A retest date says the material may be re-examined and used if it still conforms; an expiry says it may not. Printing one and meaning the other is a small dishonesty that has become a convention.

Parcel 7 reached thirty-eight degrees for nearly four hours and you then tell readers not to worry unduly. I accept the solid-state argument. I would still like to know what the material looked like on analysis, and your article does not say.

Container closure integrity is the quiet half of this subject. A perfectly filled vial with a poorly seated stopper is not a sterile product a month later, and nothing on any document describes the seal. A crimp that turns under finger pressure is a finding a buyer can make without any instrument at all.

Vacuum in a lyophilised vial is a useful and under-used indicator. A vial stoppered under partial vacuum draws diluent in when the needle is inserted; one that does not has either lost its seal or was never stoppered under vacuum. Either answer is worth knowing before you use the contents.

Price competition selects against anything that adds cost without being visible to the buyer at the point of decision. Everything discussed in this piece falls into that category, which is why none of it is offered.

Naming an absence without implying a hazard is a difficult editorial line and your department walks it more carefully than most. Saying that something is unmeasured is a statement about measurement, not about risk.

The monoisotopic against average distinction is the one I spend most time explaining. Below about two kilodaltons the monoisotopic peak is the one you can see and the one you should quote. Above it the isotope envelope broadens until the average is the honest description, and a certificate quoting a monoisotopic mass for a large peptide is quoting a peak nobody resolved.

Monoisotopic and average mass differ by enough at peptide scale to matter, and the two are quoted interchangeably in supplier literature. For a forty-residue sequence the gap is a couple of daltons, which is exactly the size of the modification a buyer might be trying to exclude.

Sixteen years in a peptide plant and I have never once been asked by a customer which ionisation source we used. I have been asked hundreds of times for a purity figure to one more decimal place.

Please keep printing the arithmetic. Readers do the sum wrong far more often than they misunderstand the pharmacology, and a worked example with the numbers visible is worth three paragraphs of explanation.

Extending an interval beyond the printed one is the departure nobody objects to and it deserves the same scrutiny as shortening it. A longer interval is safer with respect to tolerability and it also means a longer period at a dose that may not be doing much. There is a cost on both sides.

Cost is the maintenance variable that never appears in a trial protocol and dominates every real decision. An indefinite commitment priced monthly is a different proposition from a course of treatment, and the literature is written as though the two were the same shape.

The follow-up periods in this literature are shorter than the periods people are planning for by a factor of several, and that ratio deserves to be printed rather than described. Two years of evidence against a ten-year intention is a number, not an impression.

Where a reason is recorded by a clinician rather than by the person, the categories reflect what the clinician was listening for. That is not a criticism of clinicians; it is a property of any coded record, and it is rarely acknowledged in the resulting statistics.

A methodological complaint. Asking somebody for their reason implies there was one. Several of the most honest accounts I have read describe a drift rather than a decision, and a questionnaire with a list of reasons will never capture that.

A modest suggestion for the reference desk: a table of every composition substudy with its sample size, method, duration and population beside the headline ratio. It would settle a great many arguments by making the basis of each number visible at once.

Percentage of loss and absolute loss give different impressions of the same result, and writers choose between them according to the argument. Printing both is trivial and would end most of the disagreement I read.

The economics are the whole explanation. A determination costs a fraction of what a purity run costs, and it is absent because buyers do not ask for it, and buyers do not ask because they have not been told it exists.

Endotoxin is not a sterility question and the two are treated as one throughout this market. A preparation can be sterile and carry endotoxin, because the material is a fragment of a cell wall and survives the process that killed the organism.

Stopper choice belongs in this section. A stopper that has not been properly dried will release water into the headspace over months, and a cake that left the plant at one per cent moisture will not still be at one per cent when it arrives. The container is part of the formulation.

The residual moisture point is the one I would put in bold. A cake dried to one per cent water and a cake dried to four behave entirely differently over a year at the same temperature, and the certificate reports neither. Of every determination available to this trade, water content is the cheapest and the most predictive of shelf life.

The comparison your readers want is between an excursion and the stability data that would justify tolerating it. Without accelerated stability figures for the specific formulation, an excursion assessment is judgement dressed as calculation. Very few suppliers in this trade hold those figures.

On amber glass: it is not merely cheap, it is standard in the wider chemical supply trade for anything with a chromophore. The fact that this market ships peptides in clear glass is a sign of who is doing the filling more than of any decision about photostability.

The buyer-submitted result and the seller-submitted result are not the same evidence and should not be printed in the same column. Your tables do distinguish them, which I appreciate; most listings do not, and a reader comparing across sources is comparing two different experiments.

The service could close half this gap by publishing a submission protocol and refusing samples that do not follow it. Refusal is the mechanism nobody wants to use, and it is the only one that changes behaviour.

You describe blind purchasing as the gold standard. It is the minimum standard. The gold standard is blind purchasing, repeated, with retained samples, published in full including the dull results, and nothing in this market comes close to that.

As a buyer I found the section on who chose the vial genuinely clarifying and slightly deflating. I have been treating vendor-published reports as equivalent to my own submissions for two years, and on your account they are not equivalent by an amount that cannot be measured.

I have written to correct this department twice and both letters were printed with a reply that conceded the point. That is rarer than it should be and it is why I keep reading.

A withdrawal design also measures the effect of the surrounding programme falling away. Participants lose the visits, the monitoring and the contact at the same moment they lose the drug, and no published design separates those.

Where a study offered continued support to both arms, the comparison is between two managed groups rather than between management and nothing. That is a better design and a narrower question, and coverage rarely notes which was run.

Supply is a reason in this market that has no analogue in the trial literature. A source that becomes unavailable ends an arrangement as effectively as an adverse effect, and no clinical taxonomy has a category for it.

Your taxonomy would benefit from a category for external events with no relation to the arrangement at all — a house move, a family illness, a period of travel. They are common, they are not failures of anything, and they are currently distributed across every other category.

The section on who stands behind the page should mention the second signature. In a quality system the analyst performs and a reviewer approves, and the two are different people for a reason. A certificate carrying one name is a record; a certificate carrying two is a record that has been checked.

Laboratories are accountable to whoever pays them, which is ordinary commercial life. What is unusual here is that the person relying on the report is almost never that person, and there is no mechanism by which they become one.

On the recycling of a genuine document across later lots: this is the failure mode I meet most often in the wider market, and it is the hardest to characterise, because nothing on the page is false. The determination happened. It simply happened to a different batch than the one in the parcel.

On the accreditation-scope point: most private buyers will not know which accreditation body to search. It would be more useful to publish the four or five registers that cover the laboratories this market actually uses than to tell readers the registers exist.