Comparison of methods for the determination of sodium in alumina

Abstract

Four methods of determining sodium in refractory aluminas are compared: high-pressure acid dissolution, fusion with calcium metaborate, acid leaching and instrumental neutron-activation analysis. Acid leaching is shown to be unreliable; calcium metaborate fusion is suitable down to 50 µg g^–1 of sodium; high-pressure acid dissolution can be used for very pure samples (<2 µg g^–1 of sodium) without any contamination by grinding; and neutron activation gives good results with a similar limit of detection.