#hplc-massspec 2025-02-15

Saturday20 messages4 participantstimes are UTC

Highlights from this day

quiet.hours — deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant, happy to be corrected 15:49
void_volume — you need more sample for identity than for purity. plan for that when you post it tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5 15:54
void_volume — whats a normal gradient for a peptide this size 17:11
two_lifts_a_week — my peak has a shoulder on it, what does that usually mean 17:16
two_lifts_a_week — how do you spot a deletion in a sequence from mass alone you need more sample for identity than for purity. plan for that when you post it 19:33

thats co-elution

right so if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic

is there any point running a blank if the sample is the question

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quiet.hoursmod15:36

a warm transit can put a visible degradant peak on a chromatogram. that is what 5 days at ambient does

quiet.hoursmod15:49

deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant, happy to be corrected

peak   RRT    area%    note
  1   0.42     0.31    solvent front
  2   0.88     0.44    related substance
  3   1.00    98.72    main
  4   1.14     0.53    related substance

i asked Janoshik for the raw trace and they sent it. that is the right answer to that question

*that should say weekly

void_volumelab15:54

you need more sample for identity than for purity. plan for that when you post it
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5

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two_lifts_a_week 16:34

is monoisotopic or average mass the one on most certificates

plus_sixteen 16:35

do you trust an area percent from a shallow gradient

coming back to this does retention time on its own tell you what the compound is

void_volumelab16:38

a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you

void_volumelab17:10

integration choices move the number by a few tenths easily. that is most of your inter-lab variance

whats a normal gradient for a peptide this size

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right so plus sixteen, is that always oxidation

retention time is a hint

two_lifts_a_week 17:16

my peak has a shoulder on it, what does that usually mean

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two_lifts_a_week 19:30

genuine question why do two labs integrate the same peak differently

baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column

how do you spot a deletion in a sequence from mass alone
you need more sample for identity than for purity. plan for that when you post it