[vivian87]

I have a question on the BOD5 procedure.
The samples are diluted to a ratio of 1:100. Add 1ml of manganese sulfate and 1ml of alkali-iodine-oxide into the bottle. When precipitation occurs, add 1.5ml of concentrated sulfuric acid. Close the bottle and shake for several times, until all the precipitates disappear, leaving yellowish-iodine color. Then, measure 100ml of the above solution into a conical flask. titrate with 80M sodium thiosulfate. When the color becomes pale, add 5 drops of glucose/starch. Continue until all the blue color disappears.

WHY NEED TO ADD MANGANESE SULFATE, IODINE-OXIDE,SULFURIC ACID,GLUCOSE/STARCH?
FOR THE OTHER SET OF SAMPLE TO BE INCUBATED FOR 5 DAYS, SHOULD I DILUTE AND DO UNTIL ADDING SULFURIC ACID? OR JUST INCUBATE THE FRESH SAMPLE AND DILUTE AFTER 5 DAYS?

THANK YOU.