Radiotracer experiments have been used to study the retention of Na from 14M HNO3 mineralized serum samples by HAP in both batch and column processes. The specific capacity of HAP depends nonlinearly on
the ratio initial Na-amount/amount of HAP. Pre-irradiation removal of Na by HAP-columns and of Cl by evaporation permits Cu,
Mg an K in human serum to be determined by neutron activation analysis.