[carnation]

Hi all,
I have a problem when analysing organic matter in sediment. I used The Walkley and black method for analysing. This method use Potassium Dichromate as oxidant, and excess Dichromate will be titrated with Ferrous (II). However, the thing is that Sulphide was also oxidized. I don't know how to solve this problem.
If any one can help, I appreciate it very much.
Thank you.