A two-peptide blend vial holds two lyophilized peptides in one container, declared as two separate masses on the label, for example 10 mg of one peptide and 5 mg of another. Adding diluent reconstitutes both peptides in the same liquid at the same time, so the vial ends up with one total volume but two distinct concentrations, one for each component. This article works through the arithmetic: how to get each component's mg/mL, how to convert each to molarity using its own molecular weight, and how to record aliquot contents for a lab notebook.
| Item | Value used in this article | Source |
|---|---|---|
| Example blend | 10 mg tesamorelin + 5 mg ipamorelin, one vial | Matches a commercial blend format |
| Tesamorelin molecular weight | 5,135.9 g/mol (C221H366N72O67S) | PubChem CID 16137828 |
| Ipamorelin molecular weight | 711.9 g/mol (C38H49N9O5) | PubChem CID 9831659 |
| Diluent volumes worked below | 1 mL, 2 mL, 3 mL, 5 mL of bacteriostatic water | Common vial fills |
Why does a blend vial have one diluent volume but two concentrations?
The manufacturer lyophilizes two peptides into the same vial as two separate solid masses, not as one combined compound. When a researcher adds a single volume of diluent, that volume dissolves both solids at once. The total liquid volume is shared, but each peptide keeps its own declared mass, so each peptide ends up at its own mg/mL once the math is done. A blend vial is best treated as two single-peptide reconstitution problems that happen to share a denominator (the diluent volume), not as one problem with one answer.
Step one: find the mg/mL of each declared component
This is the same division used for a single-peptide vial, applied twice. For a component with mass m (mg) reconstituted in volume V (mL):
concentration (mg/mL) = m / V
A 10 mg tesamorelin + 5 mg ipamorelin vial reconstituted with 2 mL of diluent gives 10 mg / 2 mL = 5 mg/mL tesamorelin, and 5 mg / 2 mL = 2.5 mg/mL ipamorelin, in the same 2 mL of liquid. The general method for this division, and how to avoid rounding errors in it, is covered in more detail in our reconstitution calculator guide, which applies to a single peptide; the same division just needs to be run twice for a blend.
Step two: convert each mg/mL to molarity
Mass concentration (mg/mL) is not the same as molar concentration (moles of peptide per liter), because two peptides of the same mass do not contain the same number of molecules unless they have the same molecular weight. Converting requires the molecular weight of each component, in g/mol, which is calculated from its amino acid sequence and any modifications (see how peptide molecular weight is calculated from a sequence). The conversion for each component is:
molar concentration (mmol/L, equivalent to millimolar or mM) = concentration (mg/mL) × 1000 ÷ molecular weight (g/mol)
Each component uses its own molecular weight. A blend vial never has a single molarity: it has one molarity per peptide, calculated separately, because the two peptides are different molecules of different sizes.
Worked example: a 10 mg tesamorelin + 5 mg ipamorelin vial
Tesamorelin has a molecular weight of 5,135.9 g/mol and ipamorelin has a molecular weight of 711.9 g/mol (PubChem). Tesamorelin is the active ingredient in an FDA-approved prescription medicine used under medical supervision for a specific indication, described in its FDA prescribing information. The research-grade tesamorelin in this example is not that medicine, is not formulated for clinical use, and is not for human or animal use; it appears here because its published molecular weight makes the arithmetic below verifiable against a public reference. Background on this specific blend format is covered in our tesamorelin and ipamorelin monograph. The table shows mg/mL and molarity for each component at several diluent volumes:
| Diluent volume | Tesamorelin mg/mL | Tesamorelin mM | Ipamorelin mg/mL | Ipamorelin mM |
|---|---|---|---|---|
| 1 mL | 10.00 | 1.95 | 5.00 | 7.02 |
| 2 mL | 5.00 | 0.97 | 2.50 | 3.51 |
| 3 mL | 3.33 | 0.65 | 1.67 | 2.34 |
| 5 mL | 2.00 | 0.39 | 1.00 | 1.40 |
Two things stand out. First, doubling the diluent volume halves both components' mg/mL and mM figures equally, because both share the same denominator. Second, the mass ratio on the label (10 mg to 5 mg, or 2 to 1) is not the same as the molar ratio in solution. Tesamorelin's molecular weight is roughly 7.2 times ipamorelin's, so at any diluent volume the molar concentration of ipamorelin is roughly 3.6 times higher than tesamorelin's, even though its mass concentration is half of tesamorelin's. Mass ratio and molar ratio move in opposite directions here because the two peptides differ so much in size.
Recording aliquot contents in micrograms for the lab notebook
Once the mg/mL for each component is known, an aliquot's contents can be logged in micrograms without any further conversion, which is the unit most bench notebooks and sample logs use. This is bench arithmetic for labeling and tracking samples, not a dose for a subject. Using the 2 mL reconstitution from the table above, a 100 microliter aliquot contains:
tesamorelin: 5 mg/mL × 0.1 mL = 0.5 mg = 500 micrograms
ipamorelin: 2.5 mg/mL × 0.1 mL = 0.25 mg = 250 micrograms
A notebook entry or tube label for that aliquot would read something like "2 mL reconstitution, 100 microliter aliquot: 500 mcg tesamorelin + 250 mcg ipamorelin," rather than a single combined weight. Recording both components separately, by name, is what makes an aliquot traceable back to the concentration table it came from.
The blend ratio is fixed by the manufacturer
The 10 mg to 5 mg mass ratio in the worked example is set when the vial is manufactured and lyophilized. Adding more or less diluent changes both concentrations together, in the same proportion, but it cannot change the ratio between the two components, and it cannot be used to raise one component's concentration relative to the other. A study design that requires the two peptides at a specific molar ratio, or that requires varying one component independently of the other, needs two separate single-peptide vials combined by the researcher, with each vial's concentration calculated on its own, rather than a pre-blended vial. Pre-blended vials such as BPC-157 and TB-500 (see the BPC-157 + TB-500 monograph) or tesamorelin and ipamorelin, and other common two-peptide formats such as CJC-1295 (No DAC) + ipamorelin, are convenient exactly because the ratio is fixed and does not need to be measured out by hand, but that same fixed ratio is a design constraint, not a variable.
Common mistakes when working with blend vials
Treating the blend as one combined peptide
A 10 mg + 5 mg blend vial is not equivalent to 15 mg of a single peptide, because the two components have different molecular weights and different molar concentrations once reconstituted. Any concentration or molarity calculated by adding the two masses together and dividing once is wrong for both components.
Mixing up which component a concentration refers to
Because the two components share a diluent volume but not a concentration, a bare number like "5 mg/mL" is ambiguous in a blend vial unless the peptide name is attached to it. Labels, notebook entries, and aliquot tubes should always name the component next to its concentration.
Assuming the mass ratio equals the molar ratio
As shown in the worked example, a 2 to 1 mass ratio does not translate into a 2 to 1 molar ratio unless the two molecular weights happen to be equal. Study designs that reference a molar ratio need the molarity calculation, not the label's mass ratio.
Using one peptide's molecular weight for the other
Each component's molarity depends on its own molecular weight. Reusing one peptide's molecular weight to convert the other peptide's mg/mL will produce a molarity that does not correspond to either compound.
Frequently asked questions
Is a 10 mg plus 5 mg blend vial the same as a 15 mg single-peptide vial?
No. The two masses belong to two different peptides with different molecular weights, so they cannot be summed into one concentration or one molarity. Each component's mg/mL and molarity have to be calculated separately, as shown in the worked example above.
Does changing the diluent volume change the ratio between the two peptides?
No. Diluent volume is the shared denominator for both components, so adding more or less diluent scales both concentrations down or up by the same factor. The mass ratio set by the manufacturer, and the molar ratio that follows from it, stay the same regardless of diluent volume.
Can I calculate molarity without knowing the exact molecular weight?
No. Molarity depends directly on molecular weight (concentration in mg/mL times 1000, divided by molecular weight in g/mol). Without a verified molecular weight for each component, only the mg/mL figures can be calculated, not the molar concentrations.
Why does ipamorelin end up with a higher molar concentration than tesamorelin in the worked example, even though it has less mass in the vial?
Ipamorelin's molecular weight (711.9 g/mol) is much smaller than tesamorelin's (5,135.9 g/mol), so a given mass of ipamorelin contains far more molecules than the same mass of tesamorelin. Molar concentration tracks number of molecules per liter, not mass per liter, so the smaller molecule ends up at a higher molarity even at a lower mg/mL.
Where do I find the molecular weight for a specific peptide?
Molecular weight is calculated from the peptide's amino acid sequence, plus any modifications such as acetylation or amidation, as explained in our guide to calculating peptide molecular weight from a sequence. A certificate of analysis or public chemical database entry for the specific peptide is the source to use, not an assumed or rounded figure.
Is there a calculator for this kind of math?
Our reconstitution calculator guide covers the mg/mL and molarity math for a single peptide step by step. For a blend vial, the same calculator is run twice, once per component, using that component's own mass and molecular weight.
References
- National Center for Biotechnology Information, PubChem Compound Summary for CID 16137828, Tesamorelin. https://pubchem.ncbi.nlm.nih.gov/compound/Tesamorelin
- National Center for Biotechnology Information, PubChem Compound Summary for CID 9831659, Ipamorelin. https://pubchem.ncbi.nlm.nih.gov/compound/Ipamorelin
- National Center for Biotechnology Information, PubChem Compound Summary for CID 9941957, BPC-157. https://pubchem.ncbi.nlm.nih.gov/compound/Bpc-157
- U.S. Food and Drug Administration, EGRIFTA (tesamorelin for injection) prescribing information. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/022505s020lbl.pdf
- Sharma P, Dunham A. Pharmacy Calculations. StatPearls, National Center for Biotechnology Information Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK560924/
- UniProt Consortium, UniProtKB entry P62328, Thymosin beta-4. https://www.uniprot.org/uniprotkb/P62328/entry
Research use only. Homegrown Peptides products are for laboratory research and are not for human or animal use. Nothing in this article is medical advice.
