ELISA weak reaction - ELISA problem (Apr/17/2005 )

Hi All

I have a problem with the following product :

The product is : human TNF-alpha/TNFSF1A (DuoSet from R&D)
Catalog no. : DY210
I usaually use this product to measure the level of TNF cytokine in supernatents
For a long a time it works very well until recently R&D introduce a slight changes in this products
Then I got many very weak reactions of both samples and standard comparing with the results from the old kit

I do not know what is the problem and I am looking for any helpful comment from you


any comment will be much appreciated