Blank
A sample containing everything except the analyte, measured to correct for background signal.
Unit
Various
In depth
The blank accounts for absorbance by the solvent and cuvette, for contamination from reagents, and for instrumental offset. A reagent blank contains all the reagents used, while a method blank is carried through the entire procedure including sample preparation.
Examples in the real world
Zeroing a spectrophotometer on a cuvette of pure solvent before reading any standards.