Peptide storage & handling
A lyophilised peptide is a stable solid and a fragile solution. Most of what goes wrong happens in the ten minutes between opening the vial and freezing the aliquots. This is the protocol we follow ourselves.
Storing the lyophilised vial
Keep it sealed at −20 °C, dry and away from light; −80 °C for years-long storage. Kept this way a lyophilised peptide is stable for years. A few days at ambient temperature in transit does not harm the dry solid — which is why lyophilised vials ship without ice.
Before opening
Let the vial reach room temperature — about 30 minutes on the bench — before you break the seal. A cold vial opened in humid air condenses water onto the powder; lyophilised peptides are hygroscopic, and that water is the first thing that shortens their shelf life and throws off every weighing.
Choosing the solvent
Sterile or bacteriostatic water dissolves most research peptides. When it does not, the net charge decides: a basic peptide (Lys, Arg, His outnumber Asp, Glu) dissolves in 10 % acetic acid; an acidic one in a little 10 % ammonium bicarbonate; a very hydrophobic one in the smallest volume of DMSO, then diluted with buffer. Our calculator gives the net charge at pH 7 for any sequence.
Reconstituting
Run the solvent slowly down the inside wall of the vial, never onto the cake, and swirl. Do not vortex — foaming denatures and aggregates peptides. If a haze remains, sonicate for a minute or warm briefly to 30 °C. Work at the concentration you will use; dilute stock solutions keep worse than concentrated ones.
After reconstitution
Use within a few days at 2–8 °C. For anything longer, split into single-use aliquots and freeze at −20 °C — never refreeze a thawed aliquot. Sequences with Cys, Met or Trp oxidise in solution and those with Asn or Gln deamidate, so they keep worst of all; make those fresh.
Reading the counter-ion
A lyophilised peptide is a salt — usually of trifluoroacetic acid (TFA) from purification, or of acetic acid on request — and the salt is part of the labelled mass. Five milligrams of a TFA salt at 95 % purity is not five milligrams of peptide; the calculator shows the net figure for your sequence. TFA also matters biologically: at higher concentrations it is cytotoxic in cell-based assays, which is why an acetate or HCl exchange can be specified at synthesis.
The paperwork that travels with it
The lot number on the vial is the lot number on the certificate of analysis and on your invoice. The certificate reports the tests of the grade you bought — HPLC purity and MS identity at minimum — and the safety data sheet is per compound. Both are on the product page and in the CoA vault.