minimum sample size 

Synonym: minimum sample intake
https://doi.org/10.1351/goldbook.08034
Lower limit of sample size stipulated in documentation taken for chemical analysis.
Notes:
  1. Examples of documentation include a measurement procedure, product information sheets (see reference material), and reference material certificates.
  2. Values associated with performance characteristics of a measurement procedure and the property values stated in documentation are rendered invalid if the minimum sample size is not taken.
Source:
PAC, 2021, 93, 997. 'Metrological and quality concepts in analytical chemistry (IUPAC Recommendations 2021)' on page 1013 (https://doi.org/10.1515/pac-2019-0819)