make-up liquid

https://doi.org/10.1351/goldbook.12475
Solvent that is mixed with the sample flow in a liquid introduction mass spectrometry interface in order to adjust the flow rate or solvent characteristics of the system, for example, to promote ionization efficiency.
Source:
PAC, 2013, 85, 1515. (Definitions of terms relating to mass spectrometry (IUPAC Recommendations 2013)) on page 1562 [Terms] [Paper]