Supplier COA consistency: 4 batches, 2.4% purity spread — normal?

A 2.4% spread on HPLC is normal if the method or column changed. The 41-day COA lag is the part I'd flag.

What assay method though? Area % versus weight % can make the same batch look worse than it is.

This. I watched a supplier switch from HPLC-UV to LC-MS and purity numbers dropped 1.5% overnight. Not necessarily worse, just different.

Exactly. I care more about whether the same question gets the same answer twice. Inconsistent answers are the tell.

Public COAs are useful but incomplete. I'd track whether batch numbers, test dates, and lab names stay consistent across pages. A 2.4% spread isn't scary alone; a COA that changes after people ask questions is. The 41-day lag plus silence would make me wait, not write them off. What I've seen is that the reliable ones are boring: same lab, same format, dates that line up, and answers that don't drift. The sketchy ones get vague when you ask for a method or a raw chromatogram. Anyone keep a simple spreadsheet of those fields? That seems more useful than vibes.

I keep a boring sheet tracking COA date, batch ID, lab, purity, reply time. Two months in, the only vendor improving had slow replies but zero contradictions.

Four batches in six weeks is a ton of churn to try to read meaning into. I went the other way and stopped tracking supplier numbers entirely — now it's a 7-day rolling scale average plus a waist tape at the navel, same time every Sunday, 14 weeks running. My week-to-week scale noise runs about ±1.6 lb and the waist moves in 0.25" steps, and the biggest jumps I've logged had nothing to do with batch changes: five nights of 5-hour sleep plus a takeout-heavy weekend gave me a 2.4 lb blip that took six days to flatten out. Same size as the spread you're eyeballing, except I could actually explain where mine came from. The genuinely weird part is that my worst-feeling weeks were often my best scale weeks, which is what finally made me stop trusting a single number as the whole story. Do you have your own trend line running alongside those batches, or is it all supplier data right now?

Counterintuitive take from someone who's been burned by over-tracking: I quit logging COAs and started logging my own body with the same obsessive format — same scale, same time, same jeans — and my 7-day weight range last month was 3.4 lbs while my waist tape swung 0.75 in with literally nothing changed. A 2.4-point purity spread across four lots is smaller than the

I'm the opposite of a meticulous logger — didn't even take start photos, just one miserable mirror shot. But I do measure my waist every Sunday morning, same spot, and here's the weird part: weeks 3 through 6 the scale didn't budge more than half a pound, yet my waist went down almost two inches. If I'd bailed at week 6 based on the scale I'd have missed the whole point. So my honest take is stop auditing their spreadsheet and start logging your own boring weekly numbers, because 2.4 points of somebody else's lab variance won't tell you half as much as your own waist tape will.

Honestly the lag would bug me more than the spread — like last week’s weather report.

I log method details alongside lot numbers: column, wavelength, integration threshold, same lab or not. HPLC area % purity is relative; it won’t capture counterions, water, or net peptide content. A 2.4-point spread across different methods is mostly noise. Same lab/method? Then I’d want raw chromatograms and mass balance, not just the summary COA. Are your three suppliers using one third-party lab or three?

One thing I’ve started noting is arrival temp and whether the powder/cake looked intact versus collapsed, plus how it mixed. Won’t explain a 2.4% HPLC spread, but it gives me a tangible batch fingerprint alongside the COA numbers. Did your four batches differ at all visually or in how they mixed, or were they indistinguishable? I’m trying to figure out whether I’m tracking meaningful signals or just creating anxiety with more columns.

one thing I’d add: HPLC area % isn’t the same as peptide content. If the COAs don’t also list water/Karl Fischer, residual solvents, counterion/acetate or TFA, and net peptide content, a 2.4-point purity spread can partly be moisture or salt-form variance rather than synthesis quality. I track those columns separately and only compare same-lab lots. Do yours report mass balance or just the main peak? That’d tell you whether the spread is real batch variance or just the assay’s blind spot.

Sharp question: is the 2.4-point spread within one supplier’s consecutive lots, or are you pooling all three? That’s the difference between analytical noise and actual process drift. I’d track impurity profile, not just headline purity. Two lots can both read 98%; one’s a clean peak, the other is a family reunion at a different retention time. If they won’t send the chromatogram, I file the COA under “summary, unverified.” The spread matters less than whether the same shoulder keeps showing up.

The silence would bug me more than the spread, honestly.

I run a cafe, so I’m weirdly into lot codes. One thing I’d ask for: do the COAs list the same method file/analyst ID or chromatogram date across those four lots? If it’s just a new purity number but the raw data trail is copy-paste, that tells me mre than the spread. Also, are batch dates manufacture/fill dates or just

For what it's worth, i run a cafe and still get twitchy when suppliers go quiet — just tell me, lol.

That 41-day COA lag would have me refreshing my inbox like a teenager.