In analytical chemistry, a blank is a way of determining the background level detected by a method. Commonly two kinds of blanks can be used: solvent blanks and matrix blanks. A solvent blank only contains the solvents used, e.g. water, methanol, acetonitrile, often in a composition similar to that which the sample is dissolved in when analyzed.
A matrix blank will be prepared in a matrix similar to an actual sample, e.g. milk, but where it’s certain that no analyte is present. This way, it’s possible to determine if any other compounds will be detected as analyte, or if samples are becoming contaminated with analyte at any point.