#hplc-massspec 2026-05-08

Friday16 messages3 participantstimes are UTC

Highlights from this day

LC_MS_Lena — semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2 22:14
LC_MS_Lena — shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly 22:27
LC_MS_Lena — a warm transit can put a visible degradant peak on a chromatogram. that is what 5 days at ambient does 22:30
LC_MS_Lena — follow up i was wrong about tailing factor. it is usually the injection or the pH, not the column 22:59
HPLC_Hank — co-elution is the failure mode that a beautiful single peak is most likely to be hiding 23:15

tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5

semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2

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shallow gradient

do you trust an area percent from a shallow gradient

shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly

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

plus 0.98 is deamidation

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integration difference

[edited]

monoisotopic and average diverge more the bigger the molecule. say which one you are quoting

why does integration change the number so much

[edited]

follow up i was wrong about tailing factor. it is usually the injection or the pH, not the column

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thats a charge state

co-elution is the failure mode that a beautiful single peak is most likely to be hiding

M      = 4113.6
[M+2H]2+ = (4113.6 + 2.02) / 2 = 2057.8
[M+3H]3+ = (4113.6 + 3.02) / 3 = 1372.2
observed 1372.3 -> consistent

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you need more sample for identity than for purity. plan for that when you post it

ask for the trace

do the arithmetic