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c/hplc·submitted 2 months ago by u/dilara_nyberg

someone explain purity to me like I have not read a paper in years

Questionbranch of 9 comments

Slightly embarrassed to be asking this, but: someone explain purity to me like I have not read a paper in years. Sent the same vial to Janoshik and VendorInvestigate. 99.2% against a claimed 98.5%. The difference was the gradient, not the material. Why two honest labs report different numbers on the same vial. Start…

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9 comments, started 2 months ago
u/mateusz_mensah121 points·2 months ago

What wavelength, and what was the gradient?

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u/freya_baptista98 points·2 months ago

you cannot report to two decimals off that baseline

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u/phase_two_pete68 points·2 months ago

Cosigning the wavelength point. Half the disagreements in this board are two people looking at different detectors.

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u/dilara_nybergOP55 points·2 months ago

reproducibility beats resolution if you only get one of them

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u/quiet_reader_9933 points·2 months 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/sofia_petrescu11 points·2 months ago

the column has a history and it shows in the peak shape

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u/georgi_tamm2 points·2 months ago

I would not blame the sample yet. Everything you have described is consistent with the column rather than the vial.

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u/dilara_nybergOP1 point·2 months ago

a blank injection between samples costs four minutes and settles most arguments

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u/cagrilintide_enthusiast1 point·2 months ago

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

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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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