As opamp you can use LM741 or CA3140, both will work correctly at 5V supply. Other option is LM358 (dual). This IC can be supplied of almost 3V..
In this application you don't need expensive stuff from AD. Any general usage opamp capable of working in low-volt conditions can do the job.
Now, as far as 5V supply is concerned, it can be to low to operate at 20mA end, as usually one uses 250Ω termination resistor to achieve, for example, 5V for AD conversion, and that leaves no margin at all. The lowest voltage used in such a circuit should go up to at least 8V..
Regards,
IanP