Peptide reference · Lipidated 39-residue dual GIP/GLP-1 receptor agonist

Tirzepatide COA check: molecular weight, formula and what to look for

By the PeptideCOACheck team · Last updated November 2, 2026 · How we check

Use these reference values to check the identity result on a Tirzepatide Certificate of Analysis. The theoretical average molecular weight of Tirzepatide is 4,813.45 Da and the monoisotopic mass is 4,810.525 Da.

Check a Tirzepatide COA now

FP · 4,810.5249 Fingerprint calculated from the formula: positions of the protonated ions, the natural isotope pattern of the neutral molecule (relative heights are calculated; ion heights are schematic) and the atom mix. It is a reference picture, not measured data.

Tirzepatide reference data

Name	Tirzepatide
Also known as	LY3298176
Type	Lipidated 39-residue dual GIP/GLP-1 receptor agonist
Molecular formula	C₂₂₅H₃₄₈N₄₈O₆₈
Average molecular weight	4,813.45 g/mol (Da)
Monoisotopic mass	4,810.5249 Da
Residues	39
Reference source	PubChem CID 166567236 (formula and mass cross-checked)

Expected mass spectrometry ions

A Tirzepatide COA may list one of these m/z values instead of the neutral mass. That is still consistent with Tirzepatide. How charge states work.

Ion	m/z (monoisotopic)	m/z (average)
[M+3H]³⁺	1,604.52	1,605.49
[M+4H]⁴⁺	1,203.64	1,204.37
[M+5H]⁵⁺	963.11	963.70
[M+6H]⁶⁺	802.76	803.25

What else can show up on a Tirzepatide COA

Masses calculated from Tirzepatide's formula for the adducts, degradation products and synthesis impurities a lab report can show. A match tells you what the extra peak probably is.

Signal	Value	What it means
Na adduct, deconvoluted (M + 21.98)	4,832.51 Da	Sodium adduct: an MS artifact, not a separate impurity. The [M+Na]+ ion itself is at M + 22.99
K adduct, deconvoluted (M + 37.96)	4,848.48 Da	Potassium adduct: an MS artifact. The [M+K]+ ion itself is at M + 38.96
TFA adduct (M + 113.99)	4,924.52 Da	Trifluoroacetic acid from purification seen as an adduct; residual TFA salt is real vial content
M + 16 (oxidation)	4,826.52 Da	Oxidation of Trp

Adduct rows are deconvoluted masses (the shift seen against [M+H]⁺); the singly charged [M+Na]⁺ ion itself sits at M + 22.99. Deletion masses alone can't say which copy of a repeated residue is missing.

At over 4 kDa, Tirzepatide is harder to purify; 98% or higher with one sharp main peak is a strong result. The full checklist is in how to read a peptide COA.

Tirzepatide-specific things to watch

Tirzepatide is a 39-residue peptide with two Aib residues and a C20 fatty diacid side chain, giving an average mass of about 4813.5 Da.

Tirzepatide and retatrutide are similar in size (about 82 Da apart). A COA mass that matches retatrutide better than tirzepatide is a serious mismatch, and the checker will point it out.

Large lipidated peptides are harder to purify, so a single sharp HPLC main peak at 98% or higher with a disclosed column and gradient is a strong sign of quality.

Tirzepatide's charge ladder sits at 1605.5 (3+), 1204.4 (4+) and 963.7 (5+) m/z, calculated from the average mass. It has one tryptophan and no methionine, so a single +16 Da peak is the oxidation signature.

Retatrutide is only 82 Da lighter, which is why a deconvoluted mass reported to one decimal place matters more here than for most peptides. Some stores sell tirzepatide under a house name such as "Tirz (GLP-2)"; tirzepatide is not a GLP-2 agonist, so go by the mass, not the label.

Compounds with similar mass

If a COA's mass is off, compare it with these neighbors. A match to one of them can point to a mislabeled product.

Retatrutide: 4,731.35 Da (-82.10 Da)
Thymosin Beta-4: 4,963.44 Da (+149.99 Da)
Tesamorelin: 5,135.78 Da (+322.33 Da)

Sources

PubChem CID 166567236: Tirzepatide formula and reference mass.
CIAAW: Standard atomic weights: Used to calculate average molecular weights.
NIST CODATA: proton mass: Used to convert m/z charge states to neutral mass.
PeptideCOACheck methodology: How the checker's thresholds work.

Last updated November 2, 2026. Written and maintained under our editorial policy. Found an error? See corrections.

Frequently asked questions

What does 1204 m/z on a tirzepatide COA mean?

The 4+ ion of the 4813.5 Da molecule.

My tirzepatide COA reads about 4731 Da. What is it?

That matches retatrutide, not tirzepatide.

What purity is believable for tirzepatide?

98% or higher with a single sharp main peak. Lipidated peptides this size are hard to purify, so a broad or shouldered peak deserves a question.

For laboratory research use only. This page describes analytical chemistry data. It is not medical advice and makes no claim about effects in humans or animals.