Two decimal places, one injection, no procedure
This piece takes the measurement apart into the decisions it is made of, because each decision moves the answer.
Laboratory Notebook — 2025
Bench methods, bloodwork, stability, sterility.
Oxidation, and the peroxide that came in with the surfactant
Deamidation, oxidation, aggregation and hydrolysis account for nearly all of what happens to a peptide over time. Each has a characteristic residue, a characteristic…
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…
Mean kinetic temperature is not the average temperature
A single-use logger records the air adjacent to itself at a fixed interval. Where it sits in the package, and how often it samples, determine what it can possibly detect.
Why the theoretical mass on the certificate might be the wrong theoretical mass
A worked example: one peptide, five charge states, five mass-to-charge ratios, one molecular weight.
The pyrogen question has a price, and it is not the price of a purity run
A compendial sterility test takes fourteen days of incubation and consumes the containers tested. That timescale is incompatible with the business model that made…
A calculation you should do twice and write down once
Every time a vial changes, the conversion must be recalculated. Carrying forward a unit count from the last vial is the single most reliable way to give the wrong dose.
The out-of-range flag is a statistical convention with a printer attached
A flag is a probability statement about a population. It is not a statement about the person holding the printout.
How much of exenatide weight loss can any instrument actually attribute?
A body-composition report gives four decimal places and no confidence interval. That is the whole difficulty in one sentence.
The cleanroom grade nobody names on the paperwork
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.
Why your laboratory interval differs from the one in the textbook
A flag is a probability statement about a population. It is not a statement about the person holding the printout.
Why the bone question is harder than the muscle question
A plausible mechanism, a measurable change, and no outcome data. This is what an open question looks like.
HbA1c and its lag: what a result three months old is telling you
HbA1c integrates roughly three months of glycaemia with the most recent weeks weighted most heavily. Almost every misreading of it is a misreading of that weighting.
Why "muscle-sparing" is a marketing term and not a measurement
Grading six widely repeated claims against the studies actually behind them.
Why the independent testing market grew a chemistry arm and not a microbiology one
The absence of microbiological capability in this market is a commercial fact with a straightforward explanation, and it is worth understanding before blaming anybody for it.
Mean kinetic temperature is not the average temperature
The compendial definitions of cold, controlled cold and controlled room temperature permit specified excursions, and knowing the permitted band is the difference between an…
Two sessions a week, and the evidence behind the prescription
Mass and function are different endpoints and training affects them differently. Most coverage treats them as one.
Freezing a reconstituted vial: the ice-water interface problem
Bacteriostatic water contains benzyl alcohol at 0.9 per cent, which inhibits microbial growth in a preserved multiple-dose presentation. It does not sterilise a contaminated…
Tandem mass spectrometry, and the difference between weighing and reading
The Journal’s standing position: a mass that matches is necessary evidence of identity and nowhere near sufficient.
Leucine, isoleucine, and a difference no balance can measure
Deamidation adds 0.98 daltons. On a low-resolution instrument at incretin molecular weights, that is inside the noise.