spot

in chromatography
https://doi.org/10.1351/goldbook.S05889
A zone in paper and @T06346@ of approximately circular appearance.
Sources:
Orange Book, 2nd ed., p. 96 [Terms]
PAC, 1993, 65, 819. (Nomenclature for chromatography (IUPAC Recommendations 1993)) on page 834 [Terms] [Paper]