The Mendeleev Periodic Table of Chemical Elements delivered a strong impetus to the development of fundamental and applied chemistry, chemical technology, analytical chemistry, and material sciences. Each element under the Periodic Table is an idealized substance with a certain structure and properties as defined by existing theoretical frameworks. In the real world, we deal with substances that are close in composition to the element of Periodic Table under study but differ in the presence of different elements in them – impurities that distort (sometimes radically) the structure and properties of the target research object. For many centuries, humanity has sought to obtain pure substances in order to achieve desired properties. In the second half of the 20th century, a unique collection of high purity substances was created, which includes samples representing material artifacts, prototypes of elements of Periodic Table that contain record low contents of impurity elements. With ongoing scientific and technological progress, the achieved purity of substances continuously increases and, therefore, their approximation to idealized elements of Periodic Table. This is facilitated by: new technological processes for the production and storage of high purity substances with a constant decrease in the level of impurities; the creation of isotope-friendly substances; complexes of more highly sensitive multi-element analysis methods; identification of the unique properties of high purity substances, bringing them closer to the capabilities of analog elements of Periodic Table and much more. This article is devoted to progress in these areas. Special attention is also paid to the problems in modern analytical chemistry of high purity substances and the use of the latter in the metrology of chemical analysis as the standards of comparison.