For element determination, a pure material can serve as primary standard. However, real-world materials are never absolutely pure; hence, the total purity of such materials needs to be determined experimentally. A candidate material for the use as primary standard for copper determination was characterized with respect to total purity. Except the radioactive elements and noble gas, all possible impurities were measured. Based on glow discharge mass spectrometry (GDMS), inductively coupled plasma mass spectrometry (ICP-MS) and carrier gas hot extraction measurements (CGHE), the demonstrated total purity and its standard uncertainty is w(Cu) = (99.9996 ± 0.00001) %. Most of the elements with contents smaller than 0.1 mg/kg were determined by GDMS which was also used for homogeneity testing. For GDMS measurements, about 2.1 g copper shot was pressed to tablets. Both sides of the tablets were measured using GDMS (Element GD, Thermo Fisher). 73 elemental impurities in the copper were determined. With respect to relevant higher mass fractions of elements, Fe and Al were additionally determined by high-resolution ICP-MS with standard addition technique. Their values were compared with the results from GDMS. Determinations of O, N and H in the copper material by CGHE were carried out using Leco TCH600 instrument, and for C and S using Leco CS844 instrument. For O and C determination, the calibration samples Na2CO3 (GBW06101, certified reference material in China) were sealed in tin capsules and used to calibrate both of the instruments. Because of the very low contents of gas elements in the copper shot, the measurement results were mainly affected by the stability of the blank. The results of the recovery experiments by addition shown that no evidence for incomplete extraction was observed. The limits of determination of nonmetallic impurities are at the mg/kg level compared to the lg/kg level for metallic impurity measurements. Measurement methods with smaller uncertainty by improved sensitivity, higher precision and better trueness should be developed for nonmetallic impurities. The purity value and its uncertainty are dominated by the contributions from the measurements of the nonmetallic impurities, namely S, O, C and N. This example shows how important the determination of nonmetals is for the determination of the total purity of high-purity metals.

Determination of the total purity of a high-purity copper material to be used as a primary standard for element determination

2019 Spring National Meeting

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