The degree of crosslinking in a thiol-ene crosslinked hydrogel can be quantified by reacting the free thiol groups with the Ellman's reagent, DTNB. The reaction leads to a disulfide and a free TNB anion that absorbs at 412 nm. We found a thiol conversion of 77 and 78% in HA-AE and HA-NB hydrogels prepared with stochiometric concentrations of thiol and ene functions after full exposure. The incompleteness of the crosslinking reaction is attributed to the limited mobility of the dithiol crosslinkers once attached to a HA chain by one end, which reduces their probability to meet remaining alkene groups at more distant positions in the network. Such free thiols can be exploited for post-polymerization functionalization of the hydrogels.