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Single comment threadYou are looking at one branch of two labs, same vial, 98.1 and 96.4. both right? — 18 comments in the full submission. View in context.
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c/hplc·submitted 3 days ago by u/sig_figs_sam

two labs, same vial, 98.1 and 96.4. both right?

Explainerbranch of 6 comments

Yes, probably, and this thread exists so I can link it instead of retyping it. Sources of legitimate disagreement on the same physical sample, roughly in order of how much they contribute: Integration. Where the analyst draws the baseline and where they cut a shoulder. On a trace with a des-amido form eluting 0.4 min…

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This branch

6 comments, started 2 days ago
u/baseline_drifteranalytical341 points·2 days ago

Integration being first on that list is correct and under-appreciated. Two competent analysts given the same raw trace will produce different numbers, and the difference is not error, it is judgement.

Somebody should run a round-robin: one trace, twenty people, publish the spread. I suspect it would be wider than most of the vendor disputes this site has had.

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u/hplc_hobbyistruns their own column187 points·2 days ago

i said the same thing in a c/coa thread yesterday. i will post a raw trace this week if you organise it.

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u/sig_figs_samOPMOD154 points·2 days ago

Organising it. Post the trace with the method and no interpretation, I will collect submissions by modmail and publish the distribution with nobody named.

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u/peak_area_peteanalytical121 points·2 days ago

put a deliberately ambiguous shoulder in it. that is where the variance lives and a clean trace will just show everyone agreeing.

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u/hplc_hobbyistruns their own column96 points·1 days ago

i have exactly the trace for that. 97.9 with an enormous shoulder that i still cannot confidently call.

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u/rt_shift_reggie78 points·1 days ago

that is the one from the ERP thread? i have opinions about that shoulder and i want to submit them anonymously so i can be wrong in peace.

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About c/hplc

The analytical deep end: RP-HPLC methods, gradient design, integration decisions, LC-MS confirmation, amino-acid analysis, water content, and why two labs can report 98.1% and 96.4% on the same vial and both be right. Post the chromatogram, not the summary line.

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