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c/hplc·posted 2 months ago by u/ewan_tulloch

[Lab] SGN cagri — VendorInvestigate came back 93.7% against a claimed 98.6%

Lab Clean Column ×8 The Quiet One ×1 Slow Clap ×3

Confession thread, sort of.

I went from 0.25mg to 10mg much faster than I should have because the scale had stalled and I got impatient. The stall broke about 22 weeks later, at which point I had no way of knowing whether the dose increase did anything or whether it would have broken anyway.

So now I have injection-site soreness I did not need and a data point I cannot interpret. Two lessons in one.

Posting it in the hope that somebody at week 4 reads it before doing the same thing.

5,657 up / 416 down93% upvoted28 commentsid xkjfz94 May 2026

28 comments

18 in this archive, depth 4

best — the order this archive was captured in

u/saskia_bakker718 points·2 months ago

The practical rule people converge on is 28 days at fridge temperature after first puncture, and that comes from the preservative, not the peptide.

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u/naomi_antonsen606 points·2 months ago
i do not know. that is the honest answer.
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u/alcohol_aversion440 points·2 months ago

instrument quality is less important than analyst consistency

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u/peak_area_peteMOD271 points·2 months ago

Retitled to remove editorialising. Put the evidence in the body.

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[removed]175 points·2 months ago

[removed by moderator]

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u/ewan_tullochOP198 points·2 months ago

A shoulder on the main peak that 18 analysts integrated 25 different ways. Same trace, 99.3 spread.

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u/ewan_tullochOP88 points·2 months ago

axis labels included, always

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u/egfr_watcher637 points·2 months ago

a round-robin on baseline integration would be genuinely useful

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u/careful_gradient277 points·2 months ago·edited

Yeah, the chromatogram profile matters more than the headline number.

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u/rina_bergstrom435 points·2 months ago

co-elution is real and HPLC is usually not enough to resolve it

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u/matias_salgado210 points·2 months ago

Yeah, the chromatogram profile matters more than the headline number.

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u/mateusz_mensah308 points·2 months ago
i wish i had read this 24 months ago
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u/freya_baptista249 points·2 months ago

state the method: column, gradient, detection wavelength, injection volume

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u/matias_salgado200 points·2 months ago

two labs, two different baselines, two different purity numbers, both honest

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u/ewan_tulloch212 points·2 months ago

two labs, two different baselines, two different purity numbers, both honest

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u/insulin_syringe_ian118 points·2 months ago

two labs, two different baselines, two different purity numbers, both honest

Counter-anecdote: opposite result, same dose. Which mostly tells us the variance is huge.

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u/zeynep_zielinski172 points·2 months ago

two labs, two different baselines, two different purity numbers, both honest

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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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