Quick answer
AOD-9604 purity testing combines reversed-phase HPLC (purity as peak-area %) with mass spectrometry (identity) on a lot-specific certificate.
- Molecule: 16-residue hGH 177–191 fragment plus an N-terminal Tyr, with one internal Cys–Cys disulfide; about 1,815–1,817 Da
- HPLC: separates deletion products, the reduced open-chain form and dimers from the folded monomer
- Mass spec flags: about 163 Da low = missing Tyr; +2 Da = unformed disulfide
- Limits: area % says nothing about counter-ion or water content; see net peptide content
- Records: match batch number to the vial and the CoA page; calculate stock with the calculator
For laboratory research use only; not for human consumption.
What a purity and identity test has to establish for AOD-9604
AOD-9604 is a modified 16-residue fragment of human growth hormone. The sequence corresponds to residues 177–191 of hGH with one extra tyrosine added at the N-terminus (the AOD-9604 research vial lists it as Tyr-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe, with a molecular formula of C78H123N23O23S2). Two cysteines within the chain form an internal disulfide bridge. Confirming that a lot matches that exact molecule is the analytical basis for attributing a study's results to the compound itself rather than to something else in the vial.
Each structural feature maps onto a specific analytical question, which is a useful way to think about what a certificate of analysis should answer:
| Structural feature | What can go wrong | Which test reveals it |
|---|---|---|
| 16-residue chain, fixed fragment boundaries | Deletion or truncation products from incomplete coupling | HPLC (extra peaks) and mass spectrometry (lower mass) |
| Added N-terminal tyrosine | Missing tyrosine (a 177–191 fragment instead) | Mass spectrometry (about 163 Da lower) |
| Cys–Cys disulfide bridge | Reduced open-chain form; disulfide-linked dimers | Mass spectrometry (about 2 Da higher for the reduced form; roughly doubled mass for dimers) and HPLC retention |
| Intact side chains | Oxidation of the sulfur-containing groups, residual protecting groups | High-resolution mass spectrometry; HPLC pre-peaks |
Reversed-phase HPLC for AOD-9604
HPLC separates the target fragment from truncated sequences and other solid-phase-synthesis byproducts, and the resulting purity is read as described in understanding HPLC purity. For AOD-9604 specifically, the species most likely to sit close to the main peak are deletion sequences missing a single residue, the reduced (open-chain) form in which the disulfide has not closed, and disulfide-linked dimers formed when two chains pair with each other. A well-developed gradient on a C18 column resolves these from the correctly folded monomer.
The disulfide is the feature that makes this peptide more demanding than a simple linear one. A chain with two free cysteines can close intramolecularly, or it can pair intermolecularly with another chain; the second route gives a dimer that is chemically distinct but can elute near the target in a poorly optimized method. Cyclization is usually done in dilute solution to favor the intramolecular product, and a lot made at too high a concentration can carry more dimer. This is why a report that shows only a single typed percentage is much less informative than the trace behind it.
Reading the AOD-9604 chromatogram
A purity percentage is a ratio of peak areas: the area under the main AOD-9604 peak divided by the total area of every integrated peak at the detection wavelength, usually 214–220 nm, where the peptide bond absorbs. The figure therefore depends on method conditions. A shallow gradient on a C18 column resolves closely related impurities that a steep, fast gradient would fold into the main peak, so two reports quoting the same percentage are only comparable when column, gradient and wavelength are stated.
On the trace itself, look for:
- a flat baseline that returns to zero between peaks;
- a symmetrical main peak without shoulders or a split top (a shoulder often hides a co-eluting isomer);
- an integration table that lists minor peaks instead of omitting them;
- a stated sample load that keeps the main peak on scale rather than saturated, since a saturated detector under-reports the main peak's area and inflates the apparent impurity share.
Because the molecule contains tyrosine, a secondary wavelength near 280 nm gives a useful cross-check: peaks that absorb at 214 nm but not at 280 nm are less likely to be tyrosine-containing species, which helps in interpreting unknown minor peaks.
Mass spectrometry for identity
Because AOD-9604 is a fragment rather than a full-length protein, mass spectrometry is particularly useful for confirming that the fragment boundary and the added N-terminal tyrosine described in the AOD-9604 research overview are both correct. General background is in HPLC vs. mass spectrometry.
The theoretical average mass of AOD-9604 is about 1,815–1,817 Da, depending on how the formula is rounded. Electrospray instruments usually report multiply charged ions, which the software deconvolutes to a single neutral mass. A result roughly 163 Da low would point to a missing tyrosine, while a 2 Da increase is the signature of an unformed disulfide. A mass close to double the expected value points to a dimer. Observed and theoretical masses should both be printed on the report so that the difference can be checked directly.
It is worth knowing what mass spectrometry cannot do here. Isomers of the same mass, including a disulfide that is mis-paired in a different arrangement, give the same mass, so chromatographic behavior still has to carry that part of the argument.
Why it matters for isolating a metabolic-signaling readout
AOD-9604's research premise is that it isolates a specific metabolic-signaling fragment from growth hormone's broader activity (see the compound's mechanism overview). An impure lot risks reintroducing exactly the confounding activity the fragment was designed to avoid. In receptor-binding or adipocyte-culture assays, even a small percentage of an off-target species can matter if that species is more active than the fragment at the pathway being measured. Lot verification is what lets a lab state that a lipolysis-related readout came from the fragment and not from a contaminant. For a plain-language introduction to the compound, see AOD-9604 explained.
What an HPLC percentage leaves out
HPLC purity describes the peptide fraction only. A lyophilized vial also contains counter-ions left from purification, commonly trifluoroacetate or acetate, plus residual moisture, and neither appears in a UV chromatogram. Net peptide content can therefore be lower than gross powder mass even in a high-purity lot. Labs preparing quantitative stock solutions should account for this. Once the working mass is settled, the peptide calculator converts vial contents and diluent volume into a concentration in mg/mL; for a 5 mg vial reconstituted in 2 mL, for instance, the nominal concentration is 2.5 mg/mL before any net-content correction.
| Quantity | What it describes | Where it appears |
|---|---|---|
| HPLC purity (area %) | Share of the peptide signal that is the target peptide | Chromatogram and integration table |
| Identity (mass) | Whether the molecule has the expected mass | Mass spectrum, observed vs. theoretical |
| Net peptide content | Share of the powder that is peptide (rest is counter-ion and water) | Amino acid analysis or nitrogen content, if reported |
| Water content | Residual moisture in the cake | Karl Fischer titration, if reported |
Documentation to expect
A lot-specific certificate of analysis with HPLC purity and mass-spec identity is the baseline; see how to read a CoA and third-party testing explained for what separates a complete document from a summary. In practice, a complete record for an AOD-9604 lot includes:
- a lot or batch number matching the vial label;
- the HPLC chromatogram with method conditions and integrated purity;
- a mass spectrum showing observed versus theoretical mass;
- the test date and the laboratory that performed the analysis.
Batch documents are published on the certificate of analysis page. The AOD-9604 product page lists a 5 mg vial with ≥98% HPLC purity; check the CoA page for what has been published for the lot you hold, and compare its batch number against your vial.
Keeping a verified lot verified
A certificate describes a lot at the moment it was tested. The product page specifies refrigeration at 2–8 °C, with −20 °C for long-term storage, protected from heat, moisture and light; storing research peptides covers the reasoning. Reconstituted solutions degrade faster than dry powder, and a peptide with free or recently closed disulfides is sensitive to oxidation and to thiol–disulfide exchange at higher pH. Repeated freeze-thaw cycles, moisture ingress and prolonged time at room temperature can all generate new impurity peaks, so labs running long studies often aliquot material and re-test retained samples when results drift. Background on the dry state is in what is lyophilization.
Frequently asked questions
What purity level is typical for research-grade AOD-9604?
Research suppliers commonly specify 98% or higher by HPLC area, and the V8 product page lists ≥98%. The number is most meaningful when the chromatogram and method are supplied with it, so the separation behind the figure can be assessed.
Can HPLC alone confirm that a vial contains AOD-9604?
No. Retention time shows that something elutes where AOD-9604 is expected, but unrelated peptides can co-elute. Mass spectrometry supplies the independent identity check by matching the measured mass to the 16-residue sequence.
Why does the disulfide bond matter in testing?
The bridge between the two cysteines constrains the fragment's shape. Reduced or mis-paired forms are chemically different molecules, so a thorough analysis confirms the mass is consistent with the closed, monomeric form.
What mass difference would indicate a missing tyrosine?
About 163 Da lower than the expected mass. That is the residue mass of tyrosine, and it is the signature of a 177–191 fragment lacking the added N-terminal residue.
What does a mass 2 Da higher than expected mean?
It is consistent with the reduced, open-chain form in which the two cysteines carry hydrogens instead of forming the disulfide. A well-run oxidation step should leave little of this form.
Does a high HPLC purity mean the powder is 98% peptide?
No. Area percent describes the peptide signal only. Counter-ions and water add mass without absorbing UV light, so net peptide content is lower than gross weight.
Where are batch documents published?
On the certificate of analysis page. Match the batch number on your vial to the number on the document before relying on it.
How should I handle AOD-9604 between analyses?
Keep sealed vials cold, dry and dark, aliquot after reconstitution and avoid repeated freeze-thaw cycles. Re-test retained material if results drift. Concentration math is covered by the calculator.
Research Use Only. For laboratory research use only; not for human consumption. This article is research education, not usage guidance.
References
- Understanding HPLC purity (V8 Peptides)
- HPLC vs. mass spectrometry (V8 Peptides)
- How to read a certificate of analysis (V8 Peptides)
- Third-party testing explained (V8 Peptides)
- AOD-9604 research overview (V8 Peptides)
- AOD-9604 research vial (V8 Peptides product page)