In 2018 the USP-NF introduce a Content of Sodium assay to the Sodium hydroxide monograph and a Content of Potassium assay to the Potassium Hydroxide monograph, both performed by Atomic Absorption Spectroscopy (AAS). This was in addition to the Total Alkali titrimetric assay in these monographs.
These newer AAS assays immediately began causing problems generating erroneous results which did not always agree with the titrimetric assay. Investigation demonstrated that poor precision observed was related to the very large sample dilution required. The USP-NF have acknowledged the problems with these methods and are working on alternatives using ICP-OES.
Butterworths have generated alternative methods for the Content Sodium and Potassium using ICP-OES to USP-NF <1225> requirements which are ready go. These methods have demonstrated much improved precision and accuracy resolving the issues seen in the AAS tests.