A pair of cells with closely similar optical properties are called
matched cells.
One cell is the sample cell
while the other, the reference (or blank) cell
contains the solvent or a reference solution. In
double beam spectrometers,
radiation is passed either simultaneously or alternately through the
cells. In single beam instruments the cells are moved sequentially
into the radiation
beam.
Source:
PAC, 1988, 60, 1449
(Nomenclature, symbols, units and their usage in spectrochemical analysis - VII. Molecular
absorption spectroscopy, ultraviolet and visible (UV/VIS) (Recommendations 1988))
on page 1453