A chemically inert substance added to a solution to increase the volume and reduce the concentration: a diluting agent.
The term "diluent" was found in the following pages:
Material database: Princeton Applied Research - HIPA-1: Sediment for the Determination of Tributyltin
Instrument database: Teledyne CETAC Technologies - SDS-550 Sample Prep Station
Instrument database: CETAC Technologies - SDS-550 Sample Prep Station
Material database: National Research Council of Canada (NRC - CNRC) - SOPH-1 Sediment certified reference materials for the determination of tributyltin and dibutyltin
Component database: CSols Ltd - CSols AutoDil™ Software
Instrument database: Varian Inc. (Part A) - Ultramass 700 ICP-MS