Abstract: Anew mathematical model was established for investigating the sampling of twocomponent particulate mixtures by mass. By the introduction of a new concept named as logical unit of sampling by mass, equations of estimating the standard deviation and relative standard deviation of sampling by mass were presented. The physical meaning of the logical unit of sampling by mass was also studied. These equations were verified by the sampling for chemical analysis of twocomponent medicine tablets. This theory is generally applicable so as to enrich the sampling theory of analytical chemistry and direct the sampling practices.

Key words: Twocomponent particulate mixture, Sampling error, Mathematical model, Logical unit of sampling by mass