Use 490 against 630

The maximum absorption of Formazan is at 570 nm. You may try 630 nm but the signal will be much weaker and there might be interference with other substances. Better to look for a colleague with another filter set for the reader.

Yea that is the closest you can get (its not standard but I think you can write what VL u have used)....Im using 540 in my lab.

thanks all for your replies ,

i will try to find another one Dr Michael

but if i don't find  , Dr Akintunde what is meant by using 490 against 630 ?? subtraction ?

thanks for your reply Dr Nikola

yea he meant subtraction