Higher order or "definitive" methods have been in use at NIST for several decades to establish certified values for electrolytes and other trace elements in clinical Standard Reference Materials (SRMs). Although some of these methods have been described in various NIST 260 series documents, there has not been, until now, a single information resource providing comprehensive descriptions of the methods in a format which facilitates systematic updates for new methods, performance improvements to existing methods and removal of methods which are considered obsolete. This manual attempts to...