SS31 peptide purity is the number everybody quotes and hardly anybody checks. Ninety-eight percent. Ninety-nine. Ninety-nine point five. It gets printed on labels and product pages as if it settled the matter. It does not, not on its own, and we say that as people who print those numbers ourselves.
A purity figure only means something if you know how it was measured, on which lot, and what it leaves out. This article walks through six ways to check, starting with the ones that cost nothing and ending with the ones that need an instrument. You do not have to do all six. But you should know what each can and cannot tell you.
Table of Contents
Table of Contents
What purity means for SS31 peptide, and what it does not
When a supplier says a vial of SS31 peptide is 99 percent pure, they almost always mean one specific thing. A sample was run through an HPLC with a UV detector, and 99 percent of the light absorbed came from one peak. That is it.
This is a useful measurement. It is also narrower than it sounds. Three things it does not tell you:
It does not tell you what the main peak is. A sample could be 99 percent of some other peptide entirely. Purity is not identity.
It does not count things the detector cannot see. Water, salts and counter-ions do not absorb UV at the wavelength used. A vial can be 99 percent pure by HPLC and still be a fifth water and acetate by weight.
It does not tell you how much peptide is in the vial. That is a separate measurement called net peptide content, and most suppliers do not report it unless asked.
None of this is a scandal. It is simply how the measurement works. The trouble comes when a single number is treated as the whole answer.
Where the impurities in SS31 peptide come from
It helps to know what you are looking for. SS31 peptide is made by solid-phase peptide synthesis. The chain is built one amino acid at a time on a resin bead, then cut off and purified.
Each step is very efficient but never perfect. The usual by-products are these.
- Deletion sequences. A coupling step fails on some chains, so you get a three-residue peptide missing one amino acid.
- Truncated sequences. The chain stops growing early.
- Incompletely deprotected peptide. A protecting group that should have come off stays on, most often on the arginine.
- Racemised product. One amino acid flips to its mirror image. With a D-arginine already in the sequence by design, this one needs care to detect.
- Oxidised product. The dimethyltyrosine is electron-rich and can pick up an oxygen.
Because the SS31 peptide is only four residues long, there are fewer steps and fewer chances for these to build up. That is the main reason high purity is realistic for this compound. A good synthesis followed by a good preparative HPLC run will get you past 99 percent without heroics.
Way 1: Read the Certificate of Analysis line by line
This is free and takes five minutes. Every order of SS31 peptide from us ships with a COA, and you can ask for it before you buy.
Go through it like this.
The lot number
Find it. Then find the lot number on your vial. They must match. If the COA has no lot number, it is not a certificate of anything.
The date
A COA should be dated within a sensible time of manufacture. A certificate that is years older than the stock it is supposed to describe deserves a question.
The HPLC result
Look for the purity percentage and the method: column type, mobile phase, gradient, detection wavelength. Peptides are usually read at 214 or 220 nanometres, where the peptide bond absorbs. A chromatogram should be attached or available on request.
The mass spec result
The expected mass for the free base is 639.8. You should see a signal at 640.8 for the singly charged ion, or at 320.9 for the doubly charged one, depending on the instrument. If mass spec is missing, identity has not been confirmed.
Appearance and storage
White to off-white powder. Store at minus 20. If the certificate describes something different from what is in your hand, stop and ask.
Way 2: Learn to read the chromatogram
Most buyers skip the picture and look only at the number. The picture is where the information is.
A chromatogram is a line that runs flat along the bottom and jumps up into peaks. Time runs along the horizontal axis. Each peak is something coming off the column. For a clean lot of SS31 peptide you want to see one tall, narrow, symmetrical peak and very little else.
Things to look for:
- A shoulder on the main peak. This suggests an impurity that almost co-elutes, often a deletion sequence or a racemised form. The purity figure may be flattering.
- A wide, lumpy main peak. Either the column is tired or there is more than one thing under there.
- A baseline that has been cut off just above zero. Zooming the vertical axis out makes small peaks vanish. Ask for the full scale.
- A very short run. If the gradient is over in five minutes, closely related impurities may not have had time to separate.
You do not need to be an analytical chemist to spot these. You only need to have looked at a few good traces so that a bad one stands out. We are happy to talk through the trace for any lot we sell. Write to us through the contact page.
Way 3: Check identity, not only purity
We keep returning to this because it is the gap people fall into. HPLC with a UV detector tells you how many things are in the sample and in what proportion. It does not tell you what they are.
Mass spectrometry does. It weighs the molecules. SS31 peptide has a monoisotopic mass that no common by-product shares, so a clean mass spectrum with the right signal is strong evidence that the main peak is what it should be.
The best arrangement is LC-MS, where the HPLC feeds directly into the mass spectrometer and every peak gets weighed as it comes off. That way you learn not just that there is a one percent impurity but what its mass is, which usually tells you what went wrong in synthesis.
Our Ultra-Pure Research Grade and Bulk Research Grade are verified by both HPLC and mass spectrometry as a matter of course. For the other grades, mass spec data is available on request.
Way 4: Ask about net peptide content and counter-ion
If you are calculating concentrations, this matters more than the difference between 99.0 and 99.5 percent purity.
A freeze-dried peptide is a salt. The positively charged groups on SS31 peptide, and there are three of them, are each paired with a negative counter-ion. After a standard purification that counter-ion is trifluoroacetate. Many suppliers exchange it for acetate or chloride, because TFA can interfere with cell-based assays at high enough concentrations.
Three counter-ions on a molecule this small add up. Three TFA ions weigh 342, against 640 for the SS31 peptide. Add a few percent residual water, and the actual peptide in a vial of TFA salt might be only 60 to 65 percent of the powder weight. For an acetate salt it is higher, roughly 75 to 80 percent.
So ask two things. What is the counter-ion? And is the weight on the label the net peptide or the gross powder? Both ways of labelling are legitimate. You just need to know which you have. Our article on elamipretide peptide chemistry goes further into salt forms and why they matter.
Way 5: Run your own HPLC
If your lab or a core facility down the corridor has an HPLC, use it. Nothing beats your own data, and a supplier who objects to being checked is telling you something.
A basic reverse-phase method is enough.
- Column: C18, analytical scale.
- Mobile phase A: water with 0.1 percent TFA.
- Mobile phase B: acetonitrile with 0.1 percent TFA.
- Gradient: something like 5 to 60 percent B over 20 to 30 minutes.
- Detection: 214 or 220 nanometres.
SS31 peptide is quite polar, so it comes off early. If your gradient starts too high in organic solvent it will shoot through with the solvent front and you will see nothing useful. Start low.
Dissolve a small amount in water, inject, and compare your trace to the one on the COA. Retention times will differ because your system is not the supplier's. What should agree is the overall picture: one dominant peak, and impurities at about the same relative positions and sizes.
If your result is far from the certificate, do not jump to conclusions. Check your column, your sample prep and your integration settings, then contact the supplier with your data. Disagreements are usually about method differences and can be sorted out in a couple of emails.
Way 6: Send a sample for third-party testing
For work that will be audited, or for a large order where a lot depends on the outcome, an independent lab removes any doubt. You send a vial, they run HPLC and mass spec, sometimes amino acid analysis for net peptide content, and they send you a report with their own letterhead on it.
It costs money and takes a week or two. It is not something to do for every order. It makes sense in these situations:
- You are qualifying a new supplier.
- You are about to commit to a long study with a single lot.
- Your institution or a regulator requires independent verification.
- You got a strange result and want to rule the material in or out.
We support this. Third-party lot testing is available on request for our Ultra-Pure grade, and institutional buyers can ask for lot-specific documentation before purchase on bulk orders.
What the grades of SS31 peptide mean in practice
Putting this together with what we actually sell.
Standard Grade is 98 percent or better by HPLC, with a COA for every batch. Up to two percent of the UV-absorbing material is something other than the target. For screening and method work, that is fine.
High Purity Grade tightens the specification and is the one most cell culture labs use day to day.
Ultra-Pure Research Grade is 99.5 percent or better, dual verified, with full batch traceability. Half a percent or less of impurities. This is the grade to buy when the material itself might be questioned.
Bulk Research Grade is 99 percent or better, HPLC and MS verified per production lot, in vials up to 500 mg.
Which to choose is a question about the experiment, not about which number is biggest. We go through that decision in the SS31 buying guide.
Purity changes after the vial leaves us
A certificate describes the material on the day it was tested. What happens after that is up to storage and handling.
Dry SS31 peptide at minus 20 holds its purity very well. The same material left open on a bench, or dissolved and thawed ten times, does not. If you test a vial that has been badly stored and find it below specification, the synthesis is not what failed.
This is worth remembering before raising a complaint, and worth remembering when planning a long project. The eight habits that keep a lot stable are in our SS-31 peptide storage guide.
Red flags when buying SS31 peptide
We see the same warning signs often enough to list them.
- No COA, or a COA only after you have paid.
- One generic certificate for every lot.
- Purity claimed with no method stated.
- No mass spec at all.
- A chromatogram that looks like a screenshot of a screenshot, with unreadable axes.
- Prices far below the rest of the market.
- Health claims or dosing advice on the product page. A real research supplier does not give either.
One of these might be carelessness. Several together are a pattern.
How to order tested SS31 peptide from us
We sell wholesale, from a minimum of 50 units, with no upper limit. You can mix grades and sizes within an order, and other compounds such as BPC-157, GHK-Cu, TB-500 and Retatrutide count toward the minimum.
Press Order next to any size on the SS-31 peptide page. The form opens with that item filled in. Add the number of units, your delivery address and preferred payment method, and if you want to see the COA first, say so in the message. We reply by email, usually the same day, with the total, the payment details and the certificate.
Payment is by Apple Pay, Zelle, Chime, Cash App, USDT or Bitcoin. The order ships with its paperwork.
A worked example: checking one lot of SS31 peptide
Theory is easier with a case in front of you. Imagine a box of fifty 10 mg vials has just arrived, and here is what the certificate says.
Lot number: a string of letters and digits. Date of analysis: last month. Appearance: white lyophilized powder. Purity by HPLC at 220 nm: 99.6 percent. Mass by ESI-MS: found 640.4, expected 640.4 for the singly charged ion. Storage: minus 20.
Step one. Pick up a vial and read its label. Same lot number? Good. If not, stop here and write to the supplier.
Step two. Look at the chromatogram. There is one tall peak at about nine minutes. Either side of it, two or three small bumps, each well under half a percent. The baseline is flat and the scale has not been cropped. The run lasts twenty-five minutes, which is long enough for close relatives to separate. That is what a clean lot of SS31 peptide looks like.
Step three. Check the mass. 640.4 is right for the molecule plus one proton. If the spectrum is attached, you may also see a larger signal near 320.7. That is the same molecule carrying two protons, and it is normal.
Step four. Look for what is not there. This certificate does not state net peptide content or the counter-ion. So you ask. The answer comes back: acetate salt, vials filled by gross weight. Now you know that each 10 mg vial holds roughly 7.5 to 8 mg of SS31 peptide itself, and you can calculate concentrations properly.
Step five, if you have the equipment. Dissolve the contents of one vial, inject, and see whether your trace resembles the supplier's. One dominant peak, small impurities in about the same places. Done.
The whole exercise takes under an hour, most of it the HPLC run, and at the end you know more about that lot than most buyers ever find out.
Amino acid analysis, the test people forget
HPLC and mass spec get the attention. There is a third method worth knowing about, because it answers the question the other two cannot: how much peptide is actually in the powder.
In amino acid analysis, a weighed sample is broken down completely into its individual amino acids with strong acid. Those are then separated and measured. From the amounts recovered, you can work back to how much peptide was in the sample you weighed.
For SS31 peptide there is a wrinkle. Dimethyltyrosine is not a standard amino acid, so it is not in the usual calibration set, and D-arginine reads the same as ordinary arginine in a method that does not distinguish mirror images. In practice the calculation is done from arginine, lysine and phenylalanine, which is perfectly adequate.
You will not get amino acid analysis on every certificate. It is slower and dearer than HPLC. But if net peptide content matters to your work, it is the method to ask for, and an outside lab can run it for you.
Keeping purity records that will survive an audit
If your work may ever be inspected, by a funder, a journal, a quality department or a regulator, what you keep matters as much as what you test.
For each lot of SS31 peptide, hold on to these.
- The supplier's certificate, as received.
- The order confirmation showing grade, size and quantity.
- A photo or note of the vial label with its lot number.
- Your own test results, if you ran any, with the raw data files.
- The dates the lot arrived, was first opened and was used up.
- Which experiments used it.
A folder per lot, paper or electronic, is enough. The aim is that someone who was not there can trace any result back to the material that produced it. It is dull work. It is also the difference between a finding that stands and one that gets a question mark put next to it.
A note on comparing suppliers of SS31 peptide
If you are weighing two sources of SS31 peptide, ask both for the certificate of the lot they would ship today, and put the two side by side. Do not compare the headline purity. Compare the chromatograms, the run lengths, whether mass was confirmed and whether the lot numbers look real. The better SS31 peptide is usually obvious within a minute, and it is not always the one with the bigger number on the label.
Questions about SS31 peptide purity
Is 98 percent SS31 peptide good enough?
For many purposes, yes. It depends on whether two percent of related peptide impurities could affect your readout. For a first look at whether an assay responds, it rarely does.
Why is HPLC purity not the same as the amount in the vial?
Because HPLC only sees what absorbs UV. Water and counter-ions are invisible to it but still have weight. Net peptide content is the figure that accounts for them.
Can you send the COA before I order?
Yes. Ask through the contact form and name the grade and size.
What if my own test disagrees with your COA?
Send us your chromatogram and method. Most differences come down to gradient, column or integration, and we can usually work out which. If the material is at fault, we put it right.
Does higher purity SS31 peptide work better?
Not in the sense of being stronger. It contains less of other things. Whether that matters depends on how sensitive your experiment is to those other things.
Bottom line
A purity number is a starting point. Check the lot number. Look at the trace, not just the figure. Make sure identity was confirmed by mass. Ask about counter-ion and net content. Test it yourself if you can. Use an outside lab when the stakes justify it.
For a general introduction to the compound, see our essential facts about SS-31. When you are ready to order, the grades and prices are on the SS-31 peptide page.