units_pedant

Half of all mass disputes are unit errors. Daltons against atomic mass units, average against monoisotopic, ppm against millidaltons: check which pair is on the report before reading -36.5 ppm as a discrepancy.

Reported as signed ppm, which is the right convention: direction carries information about calibration that a modulus discards.

A closed balance is what converts a purity figure into a mass. 87.70 %w/w target content on a 0.1 mg claim gives 0.09 mg recovered, and every step of that is on the record.

Percent by weight of the cake throughout, stated once and applied consistently. Mixing bases across the four slots is the commonest way a balance fails to close.

Purity 97.89 % describes what fraction of the eluted material is the target. Content describes what fraction of the cake is peptide at all. Both are on this record and neither substitutes for the other.

Minutes against column volumes. Two laboratories reporting in different units and a reader assuming one of them produces an apparent drift that is purely arithmetic.

The comparison that matters is cost per milligram of recovered peptide, not cost per vial. On this lot the two differ by about a sixth.

Anhydrous salt-free content is the basis most laboratories default to and the basis fewest certificates state. Where it is stated, everything downstream becomes arithmetic.

Ion suppression from a co-eluting counter-ion at 4.00 % acetate can shift an apparent mass in a time-of-flight measurement. Desalting the injection before the mass determination removes the possibility.

Half of all mass disputes are unit errors. Daltons against atomic mass units, average against monoisotopic, ppm against millidaltons: check which pair is on the report before reading +12.3 ppm as a discrepancy.

Noted. Logged against the batch rollup.

A closed balance is what converts a purity figure into a mass. 85.35 %w/w target content on a 20 mg claim gives 19.64 mg recovered, and every step of that is on the record.