I looked up differential, but still don't savvy why the books below use 'differential' rather than 'different' and vice versa.
Advanced Organic Chemistry: Part A: Structure and Mechanisms by Francis A. Carey, Richard J. Sundberg. p 211.
Electroanalytical Chemistry: A Series of Advances edited by Allen J. Bard. p 195.
Tietz Textbook of Clinical Chemistry and Molecular Diagnostics - E-Book by Carl A. Burtis, Edward R. Ashwood, David E. Bruns. p 519.