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

the gradient question that gets asked weekly, answered properly

Questionbranch of 11 comments

the gradient question that gets asked weekly, answered properly. Making the case below, and I expect to lose some of it in the comments. Sent the same vial to PeptideMeter and Medutest. 98.2% against a claimed 97.5%. The difference was the gradient, not the material. Bought a second-hand instrument and learned more…

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11 comments, started 2 months ago
u/fatima_yildiz19 points·2 months ago

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.

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u/hplc_hobbyistMOD7 points·2 months ago

Method questions stay here; supplier claims go to c/vendorvetting with a document attached.

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u/marit_mwangi6 points·2 months ago

Ran a blank after a high-concentration injection and found the carryover I had been calling an impurity.

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u/hamza_weissOP5 points·2 months ago

system suitability before you believe any number on the run

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u/ravi_bergstrom2 points·2 months ago

integration decisions move the number more than the sample does

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u/zeynep_zielinski1 point·2 months ago·edited

integration decisions move the number more than the sample does

This is the whole methodological point of the board in one line.

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u/clara_danquah1 point·2 months ago

LC-MS for identity, UV for relative quantity

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u/hamza_weissOP2 points·2 months ago

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

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u/marit_mensa16 points·2 months ago

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

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u/dead_space_doug9 points·2 months ago

Small fix — 214nm, not 210. It matters for the comparison you are making with the other run.

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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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