In analytical chemistry, a standard solution (titrant or titrator) is a solution containing an accurately known concentration. Standard solutions are generally prepared by dissolving a solute of known mass into a solvent to a precise volume, or by diluting a solution of known concentration with more solvent.
Standard solutions are used to determine the concentration of solutions with unknown concentration, such as solutions in titrations. The concentrations of standard solutions are normally expressed in units of moles per litre (mol/L, often abbreviated to M for molarity), moles per cubic decimetre (mol/dm), kilomoles per cubic metre (kmol/m), grams per milliliters (g/mL), or in terms related to those used in particular titrations (such as titres).