saturator 

https://doi.org/10.1351/goldbook.08544
Buffer containing interfering element(s) in sufficient quantity to reach the limit of enhancement or dispersion (i.e., saturation) of the interference curve.
Source:
PAC, 2021, 93, 647. (Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)) on page 733 [Terms] [Paper]