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2 PREFACE tween editions. The year that a section was approved by the Standard Methods Committee is indicated in a footnote at the beginning of each section. Sections or methods from the Twentieth or Twenty-First Edition that are unchanged, or changed only editorially in the Twenty-Second Edition, show an approval date of 2004 or earlier. Sections or methods that were changed significantly or reaffirmed via general balloting of the Standard Methods Committee during approval of the Twenty-Second Edition, are dated 2005 through 2011. Sections or methods that were changed significantly or reaffirmed via general balloting of the Standard Methods Committee during approval of the Twenty-Third Edition, are dated after 2011. If only an individual method in a section was revised, its approval date is different from that of the rest of the section. Sections with only editorial revisions are noted as such (ie, Editorial revisions, 2015) to make it easy for users to know whether a prior method is equivalent in protocol (exclusive of the QC issues). All references to individual Standard Methods sections should include the approval year in the reference (eg, 5910-2011 or 5910-11) so users will know which version of the method was used and to facilitate the use of online versions of Standard Methods. In the Twenty-Third Edition, the Joint Task Groups that were active since the last full edition are listed at the beginning of each Part, along with a more detailed summary of changes in that Part.

Methods in the Twenty-Third Edition are divided into two fundamental classes: PROPOSED and STANDARD. Regardless of assigned class, all methods must be …