while im here i was wrong about tailing factor. it is usually the injection or the pH, not the column
#hplc-massspec 2026-04-09
Thursday25 messages4 participantstimes are UTC
Highlights from this day
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
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thats co-elution
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unrelated but does ms/ms actually prove identity or just make it very likely
i asked Medutest for the raw trace and they sent it. that is the right answer to that question
update from 6 months ago: switched to asking for the chromatogram rather than the number and it changed everything
whats a plus one dalton shift usually
coming back after 20 months, what changed in how you read these
ask for the trace
do the arithmetic
coming back to this how do you tell co-elution from a clean single peak
do you trust an area percent from a shallow gradient
you need more sample for identity than for purity. plan for that when you post it
a warm transit can put a visible degradant peak on a chromatogram. that is what 23 days at ambient does
nobody runs enough blanks, including me
show me the spectrum
[edited]two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
thats the solvent peak
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
is uv at 214 or 280 better for peptides
how would a truncation sequence show up
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relative retention time against a standard is comparable between labs. absolute minutes are not
semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
oxidation is about plus 15.99 Da and is usually methionine or tryptophan, from memory
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if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
co-elution is the failure mode that a beautiful single peak is most likely to be hiding