If you receive a certificate of analysis (COA) for tirzepatide, the two numbers that matter most are HPLC purity and confirmed molecular mass. A genuine COA shows HPLC purity above 98% and a mass spectrum that matches tirzepatide’s molecular weight of approximately 4813 daltons. Everything else on the document supports or undermines those two figures.
What HPLC Actually Measures
HPLC stands for high-performance liquid chromatography. The instrument pushes your dissolved peptide through a column packed with tiny beads. Different molecules stick to those beads for different lengths of time, so they emerge separately. A detector measures how much of each thing comes out and when.
The result is a chromatogram — a graph with peaks. The main peak is your peptide. Smaller peaks to the left or right are impurities: fragments, truncated sequences, oxidised versions of the peptide, or leftover synthesis chemicals.
Purity is reported as the area of the main peak divided by the total area of all peaks, expressed as a percentage. 98% or higher is the benchmark for research-grade tirzepatide. Below 95% should prompt questions. Below 90% means a meaningful fraction of what you weighed out is not the compound you intended to use.
A few things to check on the HPLC section of the COA:
- Retention time — the time at which the main peak appears. It should be consistent with tirzepatide’s known behaviour on a C18 reverse-phase column, typically somewhere in the 15–25 minute window depending on gradient conditions. If no retention time is listed, the chromatogram data is incomplete.
- Number of detected peaks — a clean sample has one dominant peak. Two or three small satellite peaks are normal. A forest of peaks is not.
- UV wavelength used — 220 nm is standard for peptide bonds. Some labs also run at 214 nm. Either is fine. A detection wavelength above 280 nm alone would be unusual for a peptide with no large aromatic groups.
What Mass Spectrometry Confirms
HPLC tells you how pure. Mass spectrometry (MS) tells you what. The two together are far more informative than either alone.
Mass spectrometry works by weighing individual molecules with extreme precision. The instrument strips electrons from your peptide, then measures how the charged fragments move through an electric field. The result tells you the molecular mass of what is actually in your sample.
Tirzepatide’s molecular formula gives it a monoisotopic mass of approximately 4813.5 daltons. Because tirzepatide is a 39-amino acid peptide with a fatty acid chain attached, that mass is distinctive. No common contaminant or synthesis byproduct lands at exactly the same number.
What a genuine MS result looks like:
- The spectrum shows a series of multiply-charged peaks (called charge states). Tirzepatide is large enough that it typically appears at charge states of roughly +4 to +8 in electrospray ionisation MS. Each charge state gives a different mass-to-charge ratio, but they all calculate back to the same parent mass.
- The calculated molecular weight derived from those charge states should fall within 1 dalton of 4813.5. Instruments capable of confirming peptide identity routinely achieve accuracy within 0.1–0.5 daltons.
- If the COA reports only a single peak with no charge state information, that is a low-resolution result. It is not necessarily wrong, but it is less convincing than a full spectrum.
A mass that is off by more than a few daltons points to a wrong compound, a significant modification, or a measurement error.
How the Two Tests Work Together
Consider two failure scenarios:
High HPLC purity, wrong mass. The sample is very pure — but it is not tirzepatide. This can happen if a different peptide of similar length is substituted. HPLC alone would not catch it. MS does.
Correct mass, low HPLC purity. Your sample is definitely tirzepatide, but a large fraction of it is degraded or oxidised. MS confirms identity; HPLC reveals the contamination.
Neither test alone is sufficient. A credible COA provides both, with the actual spectrum or chromatogram image attached, not just a typed number. Typed numbers without supporting data cannot be independently verified.
What Else Appears on a Complete COA
Beyond purity and identity, a thorough COA typically includes:
- Appearance — white to off-white powder, no visible clumping or discolouration
- Solubility confirmation — tirzepatide dissolves in water or dilute acetic acid
- Water content — reported as a percentage; values above 8–10% suggest the lyophilised (freeze-dried) powder absorbed moisture during storage or packaging
- Lot number and test date — lets you trace the batch if questions arise later
The test date matters. Peptide purity is measured at a point in time. A COA from several years ago tells you what the peptide was, not what it is now.
A real COA for tirzepatide shows HPLC purity at or above 98%, a confirmed molecular mass within a dalton of 4813.5, and supporting spectral data you can look at yourself. Those three things together give you a solid basis for confidence in what you have received.
NXT Labs products are sold strictly as research chemicals for in vitro research, laboratory testing and analytical purposes only, and are not intended for use in any human or animal application.
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