I want to measure the current that goes into a noninverting opamp input. I've setup my experiment as follows:

[![circuitlab schematic https://www.circuitlab.com/circuit/za4q74/input-bias-current-test/](https://i.stack.imgur.com/fNycA.png)](https://www.circuitlab.com/circuit/za4q74/input-bias-current-test/)

I can't measure the voltage drop across the 10M (R1) resistor directly since my DMM has an input impedance in the megaohm range. So, i have to measure the voltage on the ouput of the opamp. R2 is a potentiometer, so the gain is not exactly 4, and V1 is 1.19V.

When I connect the input to voltage source of 1.19V, I get 4.04V on the opamp's output. When I connect the input via the 10M resistor (R1), I get 3.64V on the output. 

Now, my gain is:

$$
4.04/1.19 = 3.39
$$

so, voltage that the opamp sees when connected via the 10M resistor is

$$
3.64/3.39 = 1.07V
$$

this means, I have a voltage drop across the resistor R1:

$$
1.19 - 1.07 = 0.12V
$$

so, the current into opamp's input is

$$
0.12V/10M = 12nA
$$

Am i doing it right?

Another question is: Could 12nA leakage current go thru a home made PCB that was vigorously cleaned from flux residue? 

[LMC6001](http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=lmc6001&fileType=pdf) has a stated input current in femtoampere range, it might be that it was overheated while soldering and went kaput. But first, I want to be sure that I'm doing the measurements the right way.