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Concentration, aliquot volume, serial dilution and molar conversion math for reconstituted peptide, worked through with the same arithmetic the calculator uses.
The first number any bench protocol needs is the concentration of the reconstituted stock, in mg/mL. That is simply the net peptide mass on the vial label divided by the volume of diluent added. A 10 mg vial reconstituted with 2 mL of diluent gives a 5 mg/mL stock; the same 10 mg reconstituted with 5 mL gives 2 mg/mL.
Recording the exact diluent volume used at the moment of reconstitution matters more than it might seem - every downstream calculation depends on that number, and it cannot be recovered later if it was not written down.
To draw a specific mass from a stock solution, divide the target mass by the stock concentration. Pulling a 250 mcg aliquot from a 5 mg/mL stock is 0.25 mg divided by 5 mg/mL, which comes to 0.05 mL. On a U-100 insulin-syringe graduation, where 100 units correspond to 1.0 mL, that reads as 5 units.
The same arithmetic runs in reverse when the volume is fixed and the mass drawn needs to be known: multiply the volume pulled by the stock concentration.
A serial dilution builds a descending concentration series by taking a fixed volume of one dilution step and adding it to a fixed volume of fresh diluent, then repeating. A 1:10 serial dilution starting from a 5 mg/mL stock produces 0.5 mg/mL, then 0.05 mg/mL, then 0.005 mg/mL, and so on - each step one-tenth of the previous.
The compounding nature of serial dilution means an error in the first step propagates through every subsequent one. Confirming the concentration of the first dilution before proceeding is worth the extra few minutes on any series longer than two or three steps.
Bench protocols defined in molar terms - micromolar or nanomolar - require converting from mg/mL using the peptide's molecular weight. Molar concentration equals mass concentration divided by molecular weight, with appropriate unit conversion: a 5 mg/mL solution of a peptide with a molecular weight of 1000 g/mol is 5 millimolar.
This conversion is where using the wrong molecular weight causes the most common bench error, particularly for co-lyophilized blends and for sequences like CJC-1295 that exist in more than one molecular-weight variant. Always confirm which specific molecular weight applies to the material actually on the bench.
CJC-1295 with DAC and without DAC differ by roughly 279 g/mol, which shifts the molar concentration of two solutions prepared at the same mg/mL by a proportional amount. A blend such as Wolverine contains two different molecular weights in one vial, so a single molar concentration figure does not describe the mixture - each component needs its own conversion using its own share of the stated mass.
For blends, calculate the concentration of each component separately using its known fraction of the total mass, rather than treating the vial's total mass as if it were one uniform substance.
The PeptideSeed reconstitution calculator performs the vial-mass-to-concentration and concentration-to-aliquot arithmetic described above, and reports how many aliquots of a chosen size a given vial yields. It is worth using even for simple cases, since it removes the risk of an arithmetic slip on a figure that every subsequent step in a protocol depends on.
It does not currently perform the molar conversion step, so that calculation should still be done by hand using the molecular weight stated on the product page for the specific sequence and variant in use.
This guide is general laboratory reference material relating to the handling of research compounds. It is not medical, veterinary or clinical guidance, and it does not describe or imply any use in humans or animals. All PeptideSeed material is supplied for in-vitro laboratory research only — see the terms of supply.