pH gradient

in electrophoresis
https://doi.org/10.1351/goldbook.P04546
The differential change of pH with distance (\(\frac{\rm{dpH}}{\rm{d}I}\)).
Source:
PAC, 1994, 66, 891. (Quantities and units for electrophoresis in the clinical laboratory (IUPAC Recommendations 1994)) on page 895 [Terms] [Paper]