This document specifies procedures for the laboratory determination of the total elemental sulfur and the sulfate half-ester content of cellulose nanocrystals (CNCs) by inductively coupled plasma-optical emission spectroscopy and conductometric titration, respectively, including sample preparation, measurement methods and data analysis. This document is applicable to the characterization of CNCs: a) with all monovalent counterions (particularly hydronium and sodium cations); b) which are either in the never-dried state in aqueous suspension, or have been redispersed from a dried form; and c) which have been extracted from any naturally occurring cellulose source using a range of sulfuric acid hydrolysis conditions, or have been sulfated post-hydrolysis using sulfuric acid.