gradient layer

in chromatography
https://doi.org/10.1351/goldbook.G02671
The chromatographic bed used in @T06346@ in which there is a gradual transition in some property.
Source:
PAC, 1993, 65, 819. (Nomenclature for chromatography (IUPAC Recommendations 1993)) on page 830 [Terms] [Paper]
See also:
Orange Book, 2nd ed., p. 98 [Terms]