According to the GOST 859-2001 and ASTM B170 standards, it is already extremely difficult to achieve a result above 99.995-99.997%, at least guaranteed and with a good chemical composition. There are certain difficulties in the classical copper production technology, as well as in other special purification technologies.

Therefore, often copper 4N5-5N and above is offered according to specifications describing its list of chemical elements for determining purity. Such a list of elements is often very different from that proposed in the GOST 859-2001 and ASTM B170 standards, but a certain purity is calculated from it. Often the rules for how to "calculate purity" are also changed - it is determined only by some of the elements even from this list of elements, and even the limits of detection when calculating purity are sometimes taken as 0. See also About Cu 5N-9N in the "Documents" section.

Copper offered in this way 5N and above often does not correspond to classical copper 4N and even often 3N, and may have the corresponding characteristics and properties. In the best cases, such copper characteristics do not differ much from the classic copper 99.99%. For example, in some serious catalogs of pure chemical elements copper "Cu 99.9999% trace metals basis" is presented. The resistivity of such "Cu 99.9999%" is indicated as 1.673 μΩ*cm, 20°C. In this case, the electrical conductivity is ~103.06% IACS. Approximately such electrical conductivity can have copper ~ 99.995-7% (depending on the specific chemical composition) according to GOST 859-2001 and ASTM B170.

 

In some tasks, it is permissible not to take into account some impurities, since copper can be contaminated to a greater extent with them in the subsequent technological process, but if in the product, then this can be critical. These moments must be distinguished, connected with the task. For example, in products in cryogenics, any impurity has an effect, to a greater or lesser extent ...