Sixteen daltons: methionine, and the easiest degradation to find
Deamidation adds 0.98 daltons. On a low-resolution instrument at incretin molecular weights, that is inside the noise.
HPLC
Page 5 of 5 of this archive, newest first.
What “LC-MS: conforms” tells a reader, which is almost nothing
None of what a checkable identity statement requires is commercially sensitive, and all of it is known to whoever produced the document.
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.
The impurity hiding underneath the parent peak
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…
A percentage is not a specification
Chromatographic purity is cheap, fast and comparable-looking. Those three properties, and not its usefulness, explain why it became the industry’s single figure of merit.
What orthogonal actually means, and what it does not
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…
D-amino acids are invisible to mass spectrometry, and that is the whole problem
Stereochemical inversion changes the molecule, changes its biology, and changes its mass by exactly nothing.
Why PeptideMeter may run electrospray where another laboratory runs MALDI
A brief and unromantic tour of the interface between a liquid sample and a vacuum.