buffer-addition technique

in analytical flame spectroscopy
https://doi.org/10.1351/goldbook.B00752
A technique in which an additive (called a spectrochemical buffer) is added to both the sample and reference solutions for the purpose of making the measure of the analyte less sensitive to variations in interferent concentration.
Source:
Orange Book, 2nd ed., p. 172 (http://media.iupac.org/publications/analytical_compendium/)