Lab tool 02 · Solution arithmetic
Solution
Calculator
Concentration, molarity and dilution arithmetic for preparing peptide solutions at the lab bench. Every result shows its working, so you can check it.
Reconstitution
The concentration a vial gives once dissolved, and the volume of solution that holds one aliquot.
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Fills in its molecular weight, computed from its sequenceFills in its molecular weight
Research use only
g/molAverage mass, for molarity
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As printed on the vial label
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Water or buffer, total
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What one aliquot holds
Readout
Concentration
2.5 mg/mL
- Per mL
- 2.5 mg
- Per µL
- 2.5 µg
- Molarity
- 1.761 mM
Aliquot volume for 100 µg
40 µL
0.04 mL
2.5 µg/µL × 40 µL = 100 µg
Assumes the stated mass is all peptide. For exact molar work, use the net peptide content where a certificate reports it; ours report HPLC purity and mass identity.
More bench arithmetic
Make up a solution, or dilute a stock
Volume for a target concentration
How much diluent gives the concentration you want.
The amount you will dissolve
In the unit chosen above
Molar units use 1419.54 g/mol from step 01.
Readout
Final volume
2.5 mL
Target = 1.409 mM at 1419.54 g/mol
5 mg ÷ 2.5 mL = 2 mg/mL
Dilution, C1V1 = C2V2
How much stock and diluent make a weaker solution.
What you have
What you want
Stock and diluent together
Stock and target share one unit, so any unit works and no molecular weight is needed.
Readout
Stock
1 mL
Diluent
9 mL
Dilution factor 10
1 mg/mL × 1 mL = 0.1 mg/mL × 10 mL
Method
The arithmetic, and what it assumes
- Concentration
- Amount ÷ volume. One mg/mL is the same as one µg/µL: that is why the two per-volume lines match.
- Molarity
- Concentration ÷ molecular weight. Catalog weights are average masses computed from each sequence. A concentration over 1,000 mg/mL or 10 M, or under 1 pg/mL (1 fM where only molar units are known), is flagged: no solution is that strong, and one that weak is almost always a slip in the units.
- Aliquot volume
- Aliquot amount ÷ concentration. The readouts flag an aliquot that is more than the vial holds, and any volume too small to pipette (under 0.1 µL).
- Dilution
- C1V1 = C2V2. Stock and target must be in the same unit, so one unit choice sets both.
- Assumptions
- The peptide dissolves fully and adds no volume, and the stated mass is all peptide. Real lots also contain water and counter-ions: for exact molar work, use the net peptide content where a certificate reports it.
- Research use
- This is laboratory arithmetic for in vitro research. It converts the numbers you enter and gives no guidance on use.