Many sulfite adducts are acid labile and, as a result, some bound SO2 is slowly released during these analyses, forming more free SO2 This leads to a systematic overestimation of free SO2. For this reason, "Free SO2" can better be characterized as "free plus some dissociated bound SO2".The amount of dissociated bound SO2 depends on the types of adducts present in the wines and the speed of the analysis