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c/hplc·posted 2 years ago by u/medutest_mel

[Lab] 14th independent test on WWB — 99.6% on a claimed 99.0%, and the trend is the interesting part

Lab The Quiet One ×3

Posting this because the title is the whole finding — 14th independent test on WWB — 99.6% on a claimed 99.0%, and the trend is the interesting part — and a number without its method is a rumour.

The relevant figures are 99.6% and 99.0%, and they come from the same log I have kept the whole time.

Area percent is the integrated area of your peak over the total integrated area at one wavelength on one gradient. Change any of those and the number changes without the sample changing.

Resolution between two peaks depends on retention, selectivity and efficiency. A shallower gradient buys retention and usually resolution, at the cost of peak width and run time.

Sceptical readings welcome. The confident ones are the ones I distrust.

0 up / 0 down49% upvoted8 commentsid sxv50626 Jun 2024
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8 comments

8 in this archive, depth 3

best — the order this archive was captured in

u/ewan_zielinski1 point·2 years ago

Carryover from a previous high-concentration injection looks exactly like a small impurity. The blank injection is four minutes and it removes the ambiguity entirely.

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u/anya_erdogan1 point·2 years ago

Started reporting my own integrations with the baseline choice stated. Arguments in my threads dropped by about half.

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u/cormac_roos1 point·2 years ago

ghost peak, check the plumbing first, it is always the plumbing

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u/nora_lundgren1 point·2 years ago

Yes — system suitability first. Without it the number is an assertion about the instrument, not the sample.

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u/sig_figs_samMOD1 point·2 years ago

Left up. The integration disagreement in this thread is the most useful thing on the board this week.

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u/ewan_zielinski1 point·2 years ago

Agreed. Two analysts, one trace, two integration choices, and a spread that has nothing to do with the vial.

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u/nora_lundgren1 point·2 years ago

Left up.

Disagreeing with this bit: that spread is ordinary inter-lab variance, not a disagreement about the material.

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u/clara_danquah1 point·2 years ago·edited

Do you have the mass, or only the UV trace?

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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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