In titrimetry, materials or groups of materials are quantified by measuring the volume of a reagent solution with known concentrations of a substance, the titrimetric solution. The titrimetric solution is used for a defined, complete chemical conversion with the materials that are to be measured. Adding a reagent until one can recognize the end point of the reaction is known as titration. The reagent is called the titrant, and the material to be tested is the sample (or analyte). The chemical conditions that are required as a prerequisite for each titrimetric determination are a defined course of the reaction between the sample and the titrant and the ability to recognize the equivalence point (or titration end point). (This paragraph is adapted, with permission, from Schwedt, 1997.)