We are doing DAC ELISA against plant viruses. I have following queries.

Controls that we are using are as follows.

Buffer control, Healthy leaf samples, disease infected sample (+ve sample), and test samples

1) what is the optimal way of analyzing the results?

2) How would you analyze the data, to say if the test sample is positive or negative

3) at times, positive control also does not show good titre value (it would be on par with Buffer control), what might be going for this situation?

Would brand of Diethanol amine when adding pNPP would cause the problem as described in (3).

Any help or guidance on this would be appreciated.

thanks,