To assess accuracy, several certred reference mate-rials ± CRM such as peridotite, PCC-1 (United States Geological Survey ± USGS); cast bronze, NBS-52-C; leaded-tin±bronze, NBS 184; steel Ni±Cr (SAE 3140) and NIST-32-E were analyzed. The obtained results can be seen in Table 1. An evaluation of these data reveals that the certi®ed values are within the calcu-lated con®dence limits (applying T-test at p