I am testing feed samples for presence of total aflatoxin using R-biopharm kit. My problem is that all samples I tested till now exhibited no signs of contamination despite that some of them are coming from farms with signs of aflatoxin toxicity. I believe that if there were a mistake it will be during extraction step which is as the following:

1. Use mixer to make the feed in fine particles

2. weight 2 g of feed

3. add 10 ml of 70% methanol

4. mix for 10 min

5. centrifuge for 10 min at 2500 x g

6. take 1 ml of the supernatant and further follow the protocol of manufacturer.

Any suggestions? thanks in advance