A stock solution is a concentrated prepared solution; working solutions are the lower-concentration dilutions made from it for an assay, often through serial dilution. This guide explains the practice and the math.
Stock vs. working solution
The stock is what you make when you reconstitute a peptide to a known concentration. A working solution is a diluted portion at the concentration an experiment actually needs; you rarely run an assay at the full stock concentration.
The dilution equation
Dilutions follow C1 × V1 = C2 × V2, where C1 and V1 are the starting concentration and volume, and C2 and V2 are the final concentration and volume. Rearranged, the volume of stock to use is V1 = (C2 × V2) ÷ C1.
Serial dilution
A serial dilution makes a range of concentrations by diluting step by step: each tube is diluted from the previous one by the same factor (for example, ten-fold each step). This produces an evenly spaced concentration range for a concentration-response experiment.
A worked example
To make 1 mL of a 10 µM working solution from a 100 µM stock: V1 = (10 µM × 1 mL) ÷ 100 µM = 0.1 mL of stock, brought up to 1 mL with solvent. For a peptide-specific version starting from vial mass, see MOTS-c 10 mg vial: stock concentration math.
Related research guides
Research-use note
This describes laboratory solution preparation for in vitro research use only.
Related research: Reconstitution Solution.
