titer
/ TY-ter /
Imagine a coin-counting machine label that says 'each turn of this crank counts 5 cents' — a fixed conversion you can apply over and over. A titer is that kind of shortcut for a titrant: a fixed amount of analyte that each unit of titrant volume corresponds to.
In classical titrimetry, the titer expresses a titrant's strength as the mass of analyte that exactly one millilitre of the titrant will react with — for example, grams of iron per millilitre of permanganate. Multiplying the titer by the volume used gives the analyte amount directly, with no fresh calculation each time.
It matters because, in routine repetitive analysis, the titer turns a burette reading straight into a result, saving steps and time. The caveat is that a titer is tied to one specific analyte and reaction; in modern usage 'titer' can also loosely mean a measured concentration, as in antibody titer, so context decides the meaning.
If a permanganate titrant has a titer of 0.005585 g of iron per millilitre, then using 20.00 mL of it means the sample contained 0.005585 × 20.00 = 0.1117 g of iron.
Titer × volume used = amount of analyte, in one step.
Do not confuse a titrant's titer (analyte mass per millilitre, for a fixed reaction) with its molar concentration. The titer bundles in the stoichiometry of one particular determination, so it is convenient but not transferable to other analytes.