primary mixture

https://doi.org/10.1351/goldbook.P04834
A mixture obtained directly from two or more components intended for the preparation of more dilute calibration mixtures (called secondary or tertiary mixtures).
Source:
PAC, 1990, 62, 2167. 'Glossary of atmospheric chemistry terms (Recommendations 1990)' on page 2208 (https://doi.org/10.1351/pac199062112167)