sorry, I'm late.
whole process is like as below.
1. take 2 grams of cheese sample into erlenmeyer flask.
2. add 0.1N HNO3 25ml and also add 0.1N AgNO3 25ml.
3. boil flask using by hotplate and make sure that cheese sample melted.
(after boiling start, normally takes 2minute)
4. after cheese melted, add 7.5%(w/v) KMnO4 10ml into flask on hotplate(still heating).
5. after liquid's color change back to light yellow, add KMnO4 5ml again.
6. wait for color change back to light yellow.
7. after color changed, take out flask from hotplate.
8. cool in room temperature 2~3min.
9. add DW 100ml and wait to flask's temperature going down room temperature.
10. after cooling, add 50%(w/v) FeNH4(SO4)2.12H2O solution 2mL.
11. titration with 0.1N NH4SCN.
thanks.