How Tesamorelin Peptide Purity Is Expressed on Documentation
A plain guide to how tesamorelin peptide purity is expressed on documentation, covering HPLC percentages, mass balance, and what a COA actually reports.
Reviewed by Yuki Tanaka, PhD, molecular biologist ·
Yuki Tanaka, PhD is a molecular biologist with a doctorate from Osaka University and postdoctoral training at Stanford School of Medicine, specializing in growth hormone axis biology, GHRH receptor signaling, and synthetic peptide analog mechanisms.
Tesamorelin peptide purity is expressed on documentation most commonly as an HPLC percentage, a single figure meant to summarize how much of the material in a vial is the intended peptide versus everything else — degradation products, truncated sequences, or residual synthesis byproducts. Reading a certificate of analysis (COA) correctly means understanding what that percentage actually measures, what method produced it, and what it leaves out.
What the purity figure represents
A purity percentage on a COA is almost always derived from high-performance liquid chromatography (HPLC). The sample is run through a column, and each distinct component elutes at its own retention time, producing a peak on a chromatogram. The area under the main peak, divided by the total area under all peaks, gives the reported purity.
This means the number is a proportion of detected peak area, not a direct count of molecules or a measure of biological activity. A listing showing “≥98% purity” is stating that, under the specific HPLC conditions used, roughly 98% of the chromatogram’s total peak area belongs to the main peak identified as tesamorelin.
Where the figure appears on a COA
A COA for tesamorelin typically includes several distinct data points, and purity is only one line among them. Documentation formats vary by supplier, but the core fields are consistent enough to compare across listings.
| COA field | What it reports |
|---|---|
| Identity / sequence confirmation | Mass spectrometry match confirming the peptide’s molecular weight against the expected sequence |
| HPLC purity | Percentage of main peak area relative to total peak area |
| Appearance | Physical description, typically a white to off-white lyophilized powder |
| Net peptide content | Percentage of the vial’s mass that is actual peptide, distinct from purity |
| Batch or lot number | Identifier tying the COA to a specific production run |
| Test date | Date the analysis was performed |
The distinction between HPLC purity and net peptide content is where confusion is most common, and it is worth separating clearly.
Purity versus net peptide content
HPLC purity describes the composition of the peptide fraction itself — how clean that fraction is relative to related impurities. Net peptide content is a separate measurement, usually from amino acid analysis or mass balance testing, that accounts for non-peptide material in the vial: counter-ions, residual salts, and bound water from the lyophilization process.
A vial can carry a high HPLC purity figure while still containing a meaningful amount of non-peptide mass. That is why some documentation lists both figures separately rather than treating “purity” as a single all-encompassing number. When only one figure is published, it is worth checking which test it corresponds to, since a listing that shows HPLC purity alone is not necessarily reporting the same thing as one that shows net peptide content.
Reading the chromatogram method
Some COAs specify the HPLC method used — reverse-phase HPLC (RP-HPLC) is the most common for tesamorelin — along with the wavelength used for detection, typically in the ultraviolet range. This detail matters because different methods can resolve impurities differently. A COA that states the method and detection wavelength gives more traceable information than one that lists only a bare percentage with no method reference.
Documentation should also specify what the reported percentage is relative to. Nearly all suppliers report purity relative to the total peak area of the sample rather than a fixed external reference, which is the standard convention for this kind of testing.
Why third-party testing changes what the figure means
A COA generated by an independent, third-party lab carries different weight than one generated in-house by the manufacturer, even when both use the same HPLC methodology. Third-party testing removes the incentive conflict of a supplier grading its own product, and it is one of the criteria worth checking before treating a purity figure as reliable documentation. Suppliers that source consistently and publish independent, batch-specific COAs for each listing are generally easier to evaluate on this basis, and catalogues like the one at HEEZ Research illustrate how batch-linked documentation is typically organized across a product line.
A worked example of interpreting a purity figure
Purity percentages do not require conversion, but they are often read alongside vial mass, so it helps to see how the two relate. Consider a vial labeled 5 mg with an HPLC purity of 99%. That means approximately 99% of the detected peak area corresponds to tesamorelin, and roughly 1% corresponds to other detected peaks (impurities or related substances).
If that vial is reconstituted with 2 mL of bacteriostatic water, the resulting concentration is 5 mg divided by 2 mL, or 2.5 mg/mL. Converting to micrograms: 2.5 mg is 2,500 mcg, so each 1 mL draw on a U-100 insulin syringe (100 units per mL) corresponds to 2,500 mcg of total peptide content at that concentration, independent of the purity figure. The purity percentage does not change this concentration math — it describes the composition of the labeled mass, not the dilution. Anyone working through reconstitution figures alongside a COA can cross-check the arithmetic with a tool such as peptcalc.com.
What documentation typically omits
A COA usually does not state stability data, such as how purity might change over time or under different storage conditions, unless a separate stability study is referenced. It also does not confirm biological activity — HPLC purity and identity testing describe the chemical composition of the sample, not whether the folded structure or receptor-binding behavior matches expectations. Listings that only cite a purity percentage without identity confirmation (mass spec) or a stated test method are giving an incomplete picture, even if the number itself looks favorable.
Summary
Tesamorelin peptide purity is expressed on documentation primarily as an HPLC-derived percentage representing the main peak’s share of total detected peak area, distinct from net peptide content and unrelated to biological activity. A complete COA states the test method, detection approach, identity confirmation, and whether testing was performed by a third party, and reading all of these fields together gives a far more accurate picture than the purity percentage alone.
A note on how to read this
This article is written for research and educational reference. The materials described are sold for laboratory research and are not for human consumption. Nothing here is dosing guidance, a prescription, or a clinical recommendation.