selective sample

https://doi.org/10.1351/goldbook.S05560
A sample that is deliberately chosen by using a sampling plan that screens out materials with certain characteristics and/or selects only material with other relevant characteristics.
Source:
PAC, 1990, 62, 1193. 'Nomenclature for sampling in analytical chemistry (Recommendations 1990)' on page 1203 (https://doi.org/10.1351/pac199062061193)