tesamorelin
Why Do Tesamorelin Listings Show Different Purity Percentages
A look at why tesamorelin listings show different purity percentages, how HPLC testing works, and what batch-level COA figures actually represent.
Medically reviewed by Catherine Dumont, MD, physician and clinical researcher — Last reviewed
Catherine Dumont, MD is a physician with clinical and research training in endocrinology and growth hormone therapeutics, with post-graduate research in GHRH analog applications and growth hormone axis disorders.
Tesamorelin listings show different purity percentages because each figure comes from a separate batch, tested at a separate point in time, sometimes with a different analytical method or a different reporting convention. A purity number on a certificate of analysis is not a fixed property of “tesamorelin” as a compound. It is a measurement of one specific production lot, and lots vary.
What a purity percentage actually measures
Most certificates of analysis (COAs) for research peptides report purity as determined by high-performance liquid chromatography, or HPLC. In simple terms, HPLC separates the components of a sample as they pass through a column, and a detector records how much material comes out at each point in time. The peptide of interest shows up as one peak among possibly several. Purity is usually expressed as the area of the main peak divided by the total area of all detected peaks, given as a percentage.
That number depends on:
- How much of the sample is the intended peptide versus truncated or incomplete sequences left over from synthesis
- How much residual solvent, salt, or coupling reagent remains after purification
- Where the lab sets its detection and integration thresholds, which affects which small peaks even get counted
- Whether the figure reported is peptide purity by HPLC alone, or purity adjusted for peptide content (which also accounts for moisture and counter-ion mass)
Two labs can run the same physical sample and report slightly different numbers if their instrument calibration, column, or integration settings differ. This is a normal source of variance in analytical chemistry, not necessarily a sign that either lab did something wrong.
Why listings disagree even for “the same” product
A listing’s purity figure only means something in the context of the batch it was measured from. Common reasons two tesamorelin listings show different purity percentages include:
- Different manufacturing batches. Synthesis runs are not identical. Even a well-controlled process produces some batch-to-batch variation in impurity profile.
- Different testing labs. Method, column type, and mobile phase can all shift the reported number slightly, even for equivalent samples.
- Age of the COA. A certificate generated at the time of synthesis reflects the product’s condition then. If a listing reuses an old COA for current stock, the number may not reflect the material actually being sold today.
- Rounding and reporting conventions. Some sellers round to the nearest whole percent; others report to one decimal place. A listing showing “99%” and another showing “98.6%” may be closer in practice than the rounded figures suggest.
- Whether the COA matches the batch at all. Some listings display a purity figure or a certificate that is not specific to the lot being shipped. This is the scenario worth the most scrutiny, since the number becomes disconnected from the product in hand.
Reading a COA instead of just the headline number
A purity percentage by itself is a thin piece of information. A useful certificate of analysis includes several supporting details that let a reader judge whether the number is trustworthy:
| COA element | What it tells you |
|---|---|
| Batch or lot number | Whether the certificate matches the specific stock being sold |
| Test date | How recent the analysis is relative to the listing |
| Testing method (e.g., HPLC, mass spec) | What kind of impurity the figure can and cannot detect |
| Testing lab name | Whether the analysis was done in-house or by an independent third party |
| Peptide content vs. HPLC purity | Whether moisture and counter-ion mass were factored in |
A listing that shows only a percentage with no batch number, no date, and no named lab gives a reader little to verify. A listing that ties a specific COA to a specific batch, from a named or independent lab, gives a reader something they can actually check.
Why third-party testing matters here
In-house testing is not inherently unreliable, but it is self-reported. Third-party testing means an outside lab, with no financial stake in the sale, ran the analysis. When comparing tesamorelin listings, a purity figure backed by an independent lab report carries more weight than the same number appearing only on the seller’s own letterhead, because it removes the seller as the sole source of the claim. Researchers comparing sourcing options can review how heezresearch.com/research/tesamorelin/ documents batch-specific testing as one example of what a fully sourced listing looks like, including a dated COA tied to a lot number.
A worked example of how purity affects apparent concentration
Purity does not change the labeled mass on a vial, but it does change how much of that mass is actually the intended peptide versus impurity. Consider a vial labeled 10 mg with a reported purity of 98%. The mass attributable to the target peptide is:
10 mg × 0.98 = 9.8 mg
Compare that to a vial labeled 10 mg at 95% purity:
10 mg × 0.95 = 9.5 mg
The difference between those two vials, in terms of peptide mass, is 0.3 mg — a small figure, but one that shows why purity and labeled mass are two separate variables that both affect what is actually in the vial. Reconstitution volume and resulting concentration are calculated from the labeled mass, not the purity-adjusted mass, which is part of why a purity percentage is reported separately rather than folded into the mg figure on the label. Researchers doing this kind of unit math sometimes cross-check their arithmetic against an independent tool such as peptcalc.com rather than relying on a single source.
What varying purity figures do and don’t tell a buyer
A range of purity percentages across listings, on its own, is not evidence that any particular listing is wrong. It reflects the reality that peptide synthesis produces batches with genuine variation, and that different labs report figures using different conventions. What separates a trustworthy listing from a weak one is not necessarily a higher number, but whether the number is traceable: tied to a batch, dated, and ideally confirmed by an independent lab. Buyers comparing sourcing options across peer tesamorelin listing catalogs can use the same checklist — batch number, test date, testing lab, and method — to judge whether a purity figure is a documented measurement or just a printed claim.
Summary
Tesamorelin listings show different purity percentages because purity is a batch-specific, lab-specific measurement rather than a fixed attribute of the compound. Variation between listings is expected. What matters more than the raw number is whether it can be traced to a specific, dated, independently verifiable certificate of analysis.