spectral subtraction 

https://doi.org/10.1351/goldbook.08290
Ordinate of one spectrum minus ordinate of another spectrum.
Notes:
  1. Spectral subtraction may be used to improve the ability to detect of minor components in the spectrum of a mixture.
  2. Successful use of the technique requires spectra, such as absorbance and Raman spectra, in which the ordinate is linear in concentration; a precisely agreeing wavenumber scale; and a very high signal-to-noise ratio.
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 674 (https://doi.org/10.1515/pac-2019-0203)