Its 0.2ul for each single reaction, at the very least i do 4 reactions.
OK, so you make a master mix, measuring 0.8 ul and aliquoting it into four 20 ul reactions? It stills seems to be a small amount of Taq per reaction -- have you tried more per reaction?
Opps left out the 0.5ul of dNTP in my orignial post (now edited)
What concentration is your dNTP mix at? My concern is that you've got a limiting reagent in your reaction somewhere because you're cutting something too fine -- if there's not enough Taq or dNTPs, or primers, then once they're used up making product (well, the Taq doesn't get used up, but it does have a half life), it's game over.
You should be using something like 0.5-2.0 units Taq, 200 μM of each dNTP, and 0.2-0.5 μM each primer. Try a reaction which uses the upper end of these ranges for each component, and see if your yield improves.
The problem with this is that, the primer sequences were previously published by my research group and that initial paper has then been expanded into what is now my phd. So my supervisor wants to stick with the same primers.
I see. And did you have a new set of these primers synthesized, or are you using old stock?