It has to be noted that a slow reaction was also observed in our
reaction systems albeit with much smaller absorbance changes. This
reaction was more prominent at excess sulfide, and its contribution
to the total absorbance changes decreased with the increase
in the DTNB concentration at excess DTNB and was not observed
at a 100 fold excess of DTNB over sulfide (i.e. at 1:1 stoichiometric
ratios)