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ForumsCOA & Analytical TestingLC-MS/MS vs HPLC for peptide analysis — November 2025

LC-MS/MS vs HPLC for peptide analysis — November 2025

HealthEcon_DC Tue, Nov 18, 2025 at 8:01 PM 29 replies 1,356 viewsPage 1 of 6
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HealthEcon_DC
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Apr 2024
Washington, DC
Nov 18, 2025 at 8:01 PM#1
Got my latest Janoshik results back and I realized a lot of people in this community don't actually know how to read an HPLC report. I work in analytical chemistry (pharma sector) so let me break this down. What you'll see on a Janoshik HPLC report: 1. Chromatogram — the actual graph with peaks. X-axis is retention time (minutes), Y-axis is signal intensity (mAU) 2. Peak table — lists each detected peak, its retention time, area, and area % 3. Purity percentage — the main peak area as a % of total peak area 4. Identity confirmation — whether the main peak's retention time matches the reference standard What "good" results look like for GLP-1 peptides: - Purity ≥ 95% = excellent, pharmaceutical grade territory - Purity 90-95% = acceptable for research peptides - Purity 85-90% = borderline, I'd want to know what the impurities are - Purity < 85% = return/discard, not worth the risk The purity number is the single most important figure. But don't ignore the rest of the data. 📊
35 5NeuroNate, JessicaH_TX, KevinCompounds and 32 others
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sophie_paris
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Nov 2024
Paris, FR
Nov 18, 2025 at 8:24 PM#2
This is so helpful. I just got my first result back — tirzepatide from [vendor]. Report says 97.3% purity with a main peak at retention time 12.4 min. There are two small impurity peaks at 8.2 min (1.1%) and 14.7 min (1.6%). Is this good? Should I be worried about those impurity peaks?
34 4CryptoCarl, MariaRD, AussieAnna and 31 others
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CarlaRPh_TPA
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Jan 2024
Tampa, FL
Nov 18, 2025 at 8:47 PM#3
97.3% is excellent — that's genuinely pharmaceutical grade purity. For context, the FDA approval for Mounjaro (brand tirzepatide) requires ≥95% purity. Those small impurity peaks at 1.1% and 1.6% are completely normal and expected in peptide synthesis. They're most likely: - Truncated sequences — shorter versions of the peptide that didn't fully synthesize - Oxidized forms — the peptide with a slightly modified amino acid - Deletion peptides — missing one amino acid in the chain None of these are dangerous at those levels. They're just inactive or minimally active fragments. You'd need impurities above 5% before I'd start asking questions about what they actually are. Your vendor did well on this batch. 👍
Last edited: Nov 19, 2025 at 12:47 AM
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Dr.ReproEndo
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Scottsdale, AZ
Nov 18, 2025 at 9:10 PM#4
Good breakdown. Let me add something about retention time because this is how identity is confirmed. Every compound has a characteristic retention time on a given HPLC column under specific conditions. Janoshik runs reference standards alongside your sample. If your sample's main peak elutes at the same time (±0.2 min typically) as the reference standard, that confirms identity. > If the purity is 98% but the retention time doesn't match the reference standard, you have a very pure sample of the wrong compound. This has happened. I've seen a result where someone sent in "semaglutide" and it came back 96% pure — but the retention time matched BPC-157, not semaglutide. The vendor had mislabeled the vials. Without the identity confirmation, you'd think everything was fine. Always check the identity match, not just the purity number.
32 2GraceAZ_72, carl_compliance, DanielChem_CHI and 29 others
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alex_tucson
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May 2024
Tucson, AZ
Nov 18, 2025 at 11:16 PM#5
Wow, that's terrifying. So a bad actor could sell literally anything and if you only looked at purity %, you'd never know?
31 1FDA_TrackerJim, ricardo_MIA, BrianDallas92 and 28 others
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