I am developing a redox titration method to assay Sodium Selenite in a pharmaceutical product. The method that I have developed is a redox back titration with Iodine 0.1N and Sodium Thiosulfate 0.1 N as titration solution. The problem with the titration is that my recovery is to low.

After some research it seems that the emulsifiers are forming micelles. This micelles encapsulate the Sodium Selenite. The emulsifiers are Polysorbate 80 and Sorbitan stearate. Does anyone knows how to decapsulate the sodium selenite out of these emulsifiers?