MOTS-c Reconstitution — Volume and Concentration Reference

Published 2026-10-15 · Lyophile Editorial

Reconstituting MOTS-c is arithmetic, not guesswork. A 10 mg vial brought up in 2 mL of diluent gives 5,000 mcg/mL, which on a U-100 insulin syringe works out to 50 mcg per unit. Every number on this page follows from that one relationship: mass of peptide divided by volume of diluent equals concentration, and concentration divided by 100 equals micrograms per unit.

Work the math below with your own vial size, then use the tables to compare concentration options before you commit to a diluent volume. For research use only — not clinical guidance.

MOTS-c reconstitution calculator: how do I work out concentration and units per syringe?

Concentration equals vial mass in micrograms divided by diluent volume in milliliters. A 10 mg vial is 10,000 mcg; in 2 mL that is 5,000 mcg/mL. Divide by 100 to convert to U-100 units: 50 mcg per unit. The table below runs the common vial sizes across four diluent volumes.

| Vial (mg) | Diluent | Concentration | mcg per U-100 unit | 1 unit delivers | |---|---|---|---|---| | 5 mg | 1 mL | 5,000 mcg/mL | 50 mcg | 0.01 mL | | 5 mg | 2 mL | 2,500 mcg/mL | 25 mcg | 0.01 mL | | 5 mg | 3 mL | 1,667 mcg/mL | 16.7 mcg | 0.01 mL | | 10 mg | 1 mL | 10,000 mcg/mL | 100 mcg | 0.01 mL | | 10 mg | 2 mL | 5,000 mcg/mL | 50 mcg | 0.01 mL | | 10 mg | 3 mL | 3,333 mcg/mL | 33.3 mcg | 0.01 mL | | 10 mg | 5 mL | 2,000 mcg/mL | 20 mcg | 0.01 mL | | 20 mg | 2 mL | 10,000 mcg/mL | 100 mcg | 0.01 mL | | 20 mg | 4 mL | 5,000 mcg/mL | 50 mcg | 0.01 mL |

Two things about that table matter more than the rest. First, the unit column never changes — a U-100 syringe is defined as 100 units per mL, so one unit is always 0.01 mL regardless of what is dissolved in it. Second, the mcg-per-unit figure is the only number you need at the bench, because it converts a syringe reading directly into mass without a second calculation.

The step-by-step math

1. Convert vial mass to micrograms. 1 mg = 1,000 mcg. A 10 mg vial is 10,000 mcg.
2. Divide by diluent volume in mL. 10,000 mcg ÷ 2 mL = 5,000 mcg/mL.
3. Convert to units. 5,000 mcg/mL ÷ 100 units/mL = 50 mcg per unit.
4. Read the syringe. A draw to the 10-unit mark delivers 10 × 50 = 500 mcg.

If you would rather work backwards — you know the mass you want per aliquot and need to pick a diluent volume — rearrange step 2: diluent volume = vial mass ÷ target concentration. A 5 mg vial at a target of 2,000 mcg/mL needs 5,000 ÷ 2,000 = 2.5 mL.

How much bacteriostatic water for a 5 mg MOTS-c vial?

A 5 mg MOTS-c vial reconstituted with 2 mL of bacteriostatic water yields 2,500 mcg/mL, or 25 mcg per unit on a U-100 insulin syringe. The same vial in 1 mL gives 5,000 mcg/mL and 50 mcg per unit; in 2.5 mL it gives 2,000 mcg/mL and 20 mcg per unit. Diluent volume is a resolution choice, not a potency choice — total peptide mass in the vial is unchanged.

That last point is the one people get wrong. Adding more water does not weaken the vial; it spreads the same mass across a larger volume, which makes small aliquots easier to measure accurately and large ones harder. There is a practical floor and ceiling here. Below roughly 0.5 mL of diluent in a standard 3 mL vial, the liquid film left on the glass wall becomes a meaningful fraction of the total, and recovery suffers. Above roughly 5 mL in the same vial, you are drawing volumes that a 1 mL insulin syringe cannot hold in one pull.

What concentration should I pick for a 10 mg vial?

Pick the concentration that puts your working aliquot in the middle third of the syringe barrel. For a 10 mg vial, 2 mL of diluent gives 5,000 mcg/mL and 50 mcg per unit, which places a 500 mcg aliquot at the 10-unit mark — readable, repeatable, and well away from the zero line where graduation error is largest.

The middle-third rule is worth stating plainly because it is the difference between a clean draw and a sloppy one. Insulin syringe accuracy degrades at both ends: the first two or three units sit under the needle hub where the scale is compressed, and the final units near the plunger stop are hard to read against the flange. Aim for aliquots landing between roughly 20% and 80% of barrel capacity.

| Working aliquot | Best-fit concentration | Units drawn | Diluent for 10 mg vial | |---|---|---|---| | 100 mcg | 2,000 mcg/mL | 5 units | 5 mL | | 250 mcg | 2,500 mcg/mL | 10 units | 4 mL | | 500 mcg | 5,000 mcg/mL | 10 units | 2 mL | | 1,000 mcg | 10,000 mcg/mL | 10 units | 1 mL | | 2,000 mcg | 10,000 mcg/mL | 20 units | 1 mL |

Note that the 5-unit draw in the first row is below the comfortable reading zone — if that is your target, a 2 mL diluent volume (25 mcg per unit, 4 units drawn) is worse, and a 10 mL volume (1,000 mcg/mL, 10 units drawn) is better but may exceed what the vial comfortably holds. This is where vial size and diluent volume have to be solved together rather than one at a time.

Reconstitution steps in plain English

Swab the stopper with 70% isopropyl alcohol and let it air-dry fully — a wet stopper wicks liquid and defeats the swab. Draw your diluent volume into a syringe, then insert the needle at a slight angle so the stream runs down the glass wall rather than striking the lyophilized cake directly. Direct impact foams the powder and can denature peptide at the air-liquid interface.

Swirl; do not shake. Dissolution of a typical lyophilized peptide at 2–5 mg/mL usually completes within a few minutes at room temperature. If the cake resists, let the vial stand rather than adding agitation. Once clear, inspect against a dark background for particulates — USP <790> sets the visible particulate standard for injections, and while that chapter governs finished pharmaceuticals rather than research material, the inspection method is the same and costs nothing.

Label the vial with date, diluent volume, and resulting concentration. Concentration is the number that gets forgotten, and it is the only one that matters three weeks later.

Does benzyl alcohol in bacteriostatic water affect the math?

No. Benzyl alcohol at the typical 0.9% w/v concentration in bacteriostatic water changes the diluent's preservative properties, not its volume, so concentration math is identical to using sterile water. The 0.9% figure is the common formulation; bacteriostatic water is not a USP-designated article the way Bacteriostatic Sodium Chloride Injection is under USP monograph standards, so verify the label on whatever you have.

The trade-off is real, though. Benzyl alcohol is bacteriostatic — it inhibits bacterial proliferation, which is why multi-dose vials can be entered repeatedly. It is not a sterilant and does not neutralize endotoxin. It is also incompatible with a handful of peptides, and it is not recommended for use in neonates per labeling on benzyl alcohol-containing products. For research planning, the practical question is whether your protocol involves repeated entries from one vial over weeks; if yes, bacteriostatic water is the standard choice, and if the peptide is sensitive to the preservative, sterile water plus single-use aliquoting is the alternative.

Common failure modes

Forgetting that the powder volume is not zero. A lyophilized cake occupies space, so the final volume is slightly greater than the diluent you added — typically by a small percentage at 2–5 mg/mL. At high concentrations this shifts the true concentration downward by a few percent. It is not correctable without measuring, which is why gravimetric reconstitution (weighing the vial before and after adding diluent, assuming a density near 1.0 g/mL for dilute aqueous solutions) is the reference method when accuracy matters.

Reading the wrong scale. Some insulin syringes are marked in half-units or have dual scales. Confirm the barrel is U-100 before you multiply by anything.

Assuming a 1 mL syringe and a 0.3 mL syringe have the same resolution. They do not. A 0.3 mL U-100 syringe resolves to 0.01 mL per unit across a shorter barrel, so each unit is physically larger and easier to read — worth the switch when your aliquot is under 10 units.

Reconstituting with cold diluent. Cold slows dissolution and can promote aggregation in some sequences. Room temperature is the default unless the supplier's published specification says otherwise.

Where to source bacteriostatic water

• BAC Water Depot — bacteriostatic water in sealed multi-dose vials
• Med Lab Supply — sterile diluents and lab consumables
• Research Supply Co — bulk diluent options for multi-vial work

Where to source research peptides

• Alpha Amino USA — per-lot HPLC/MS COA, US-shipped
• Lot Verified Peptides — third-party tested, COA on request
• Peptide Standards Lab — research-grade lyophilized material

For research use only — not clinical guidance.