Scope
This guide is about making stock solutions in the laboratory: choosing a solvent, dissolving a lyophilised powder cleanly, working out the concentration of the result, and storing it. Everything sold by BuyUK Peptides is for in-vitro laboratory research only, and nothing here describes, or should be read as describing, preparation or use of any compound in people or animals.
Why peptides arrive as a powder
Peptides are supplied lyophilised, freeze-dried from solution under vacuum, because in the dry state most of the chemical reactions that degrade them in water (hydrolysis, deamidation, oxidation, aggregation) slow almost to a stop. The price is that every experiment begins with reconstitution, and a careless one can lose part of the material to incomplete dissolution, aggregation or adsorption before the experiment starts.
The solvents
Sterile water. The simplest choice and the one with nothing to interfere downstream. It has no preservative, so a solution made in it should be used promptly or aliquoted and frozen.
Bacteriostatic water. Sterile water with 0.9% benzyl alcohol as a preservative, which suppresses microbial growth in a vial that is entered repeatedly [1]. It is the usual default for the short, hydrophilic peptides in the catalogue. Two cautions apply. Benzyl alcohol is not inert to cultured cells, so a stock made in it should be diluted substantially into medium; and it can denature folded proteins over time, so it is the wrong choice for IGF-1 LR3.
Dilute acetic acid. 0.6% acetic acid, about 0.1 mol/L and pH 3, protonates basic side chains and the N-terminus so that peptides carrying little net charge at neutral pH repel one another and dissolve rather than aggregate. Dissolve in a small volume first, then dilute with water or buffer to the final concentration.
Dilute hydrochloric acid. 10 mmol/L HCl is the conventional solvent for recombinant IGF-1 and its analogues, which are most soluble and stable slightly acidic and at high concentration.
DMSO. For very hydrophobic sequences or small molecules, a small volume of DMSO dissolves the material before dilution into aqueous buffer. Keep the final DMSO concentration in a cell assay as low as the design allows, and include a vehicle control.
Buffers to avoid. Do not dissolve the copper peptides in chelating buffers (EDTA, citrate, high-concentration phosphate or Tris), which strip the copper. Do not dissolve NAD+ in alkaline buffer, in which it breaks down.
Which solvent for which compound
| Compound or class | First choice | Notes |
|---|---|---|
| BPC-157, TB-500, KPV, Epithalon, AOD-9604 | Water or bacteriostatic water | Dissolve at once |
| Ipamorelin, hexarelin | Water or bacteriostatic water | Hexarelin is light-sensitive |
| CJC-1295 (no DAC), sermorelin, tesamorelin | Water; dilute acetic acid if hazy | Sermorelin and tesamorelin carry Asn8 and Met27, prone to deamidation and oxidation; CJC-1295 (no DAC) replaces both |
| Semaglutide, tirzepatide, GLP-3, cagrilintide, survodutide, mazdutide | Water or bacteriostatic water, near-neutral pH | Lipidated: use low-binding tubes, swirl rather than shake |
| GHK-Cu, AHK-Cu | Water | Avoid acid and chelating buffers; the solution should stay blue |
| MT-2, PT-141 | Water or bacteriostatic water | Protect from light |
| MOTS-c, SS-31 | Water | MOTS-c has two methionines; keep cold and dark |
| Semax, Selank, thymosin alpha-1 | Water or bacteriostatic water | Selank is strongly basic; use low-binding plastic at low concentration |
| IGF-1 LR3 | 10 mmol/L HCl or 0.1 mol/L acetic acid | Not bacteriostatic water; aliquot and freeze |
| NAD+ | Neutral buffer or water, freshly made | Unstable in alkaline solution |
| 5-Amino-1MQ | Water or DMSO | A small molecule; dissolves at once |
Each monograph in the compound library gives the detail for that compound.
Dissolving cleanly
Let a refrigerated vial reach room temperature before opening, so that moisture does not condense on the powder. Work aseptically if the solution is for cell culture. Add the solvent slowly down the inside wall of the vial rather than onto the cake, then swirl gently. Do not shake or vortex: agitation foams and aggregates peptides, especially the lipidated ones and anything with a folded structure. Allow a minute or two for larger peptides to dissolve. The result should be clear and colourless (blue for the copper complexes); persistent haze means the solvent is wrong for that compound, not that more shaking is needed. Where a sterile solution is required, filter through a 0.22 µm PES or PVDF membrane, not nylon, which binds lipidated peptides.
Working out the concentration
Concentration by mass is the vial content divided by the volume added. A 10 mg vial dissolved in 2 mL gives 5 mg/mL, which is also 5 µg/µL. Two corrections make the figure accurate. First, lyophilised peptides contain water and counter-ions, so if the certificate reports net peptide content, multiply the vial mass by that fraction: at 85% net content, the same solution holds 4.25 mg/mL of peptide. Second, for most assays the useful unit is molar. Divide the mass concentration by the molecular weight: 5 mg/mL of tirzepatide (4,813.5 g/mol) is about 1.04 mmol/L, while 5 mg/mL of BPC-157 (1,419.6 g/mol) is about 3.52 mmol/L. The peptide calculator do this arithmetic.
Aliquoting and storage
Make a concentrated stock, divide it at once into single-use aliquots in low-binding tubes, and freeze them at −20 °C or, for the longest storage, −80 °C. Thaw each aliquot once and discard what is left. Repeated freezing and thawing is the commonest avoidable cause of lost activity. As a general guide, stocks of short, stable peptides keep for several weeks at 2 to 8 °C and for months frozen; peptides with methionine, cysteine, tryptophan or asparagine-glycine motifs, and folded proteins such as IGF-1 LR3, should be frozen from the start. Label every aliquot with the compound, concentration, solvent, batch number and date. The storage and stability guide gives compound-by-compound figures.
References
- Pfizer (Hospira). Bacteriostatic Water for Injection, USP: prescribing information. labeling.pfizer.com. Accessed October 2026.
This monograph summarises the published literature for laboratory researchers. It is not medical advice, and nothing on this site is for human or veterinary use.