AN-1798 LMP7721 Potentiostatic Circuit

Hello,

I have built the Potentiostatic circuit in AN-1798:

http://www.ti.com/lit/an/snoa514c/snoa514c.pdf

I have chosen a value of 10 Ohms for R6.  The only P-type JFET I could source was a 2N5462.

I am not sure how the first stage Op-Amp works?  How do I set the reference voltage?

Thank you.