liquid-phase film thickness

symbol: $d_{\rm{f}}$
https://doi.org/10.1351/goldbook.09900
Average thickness of the liquid stationary phase film coated on the inside wall of the column tubing of an open-tubular column.
Source:
PAC, 2017, 90, 181. (Terminology of separation methods (IUPAC Recommendations 2017)) on page 191 [Terms] [Paper]