additive matrix effect 

Synonyms: background interference, translational matrix effect
https://doi.org/10.1351/goldbook.08005
Matrix effect that is independent of the measured quantity value of the measurand.
Notes:
  1. An additive matrix effect affects the intercept, not the slope, of a linear calibration curve.
  2. The effect is sometimes termed "translational matrix effect" or "background interference".
Examples:
  1. An additive matrix effect that originates from a missing or flawed blank correction.
  2. The measurement of plutonium mass concentration using a K-edge densitometer in the presence of a uranium admixture. The presence of uranium causes a large additive matrix effect.
Source:
PAC, 2021, 93, 997. 'Metrological and quality concepts in analytical chemistry (IUPAC Recommendations 2021)' on page 999 (https://doi.org/10.1515/pac-2019-0819)