Mak,
Do you need to measure both + and - voltages on the same input? In other words does the signal swing from +2V to -2V?

If so, then you must use an op-amp (LM324 or equivalent) and offset the input to the op-amp by 2V. So -2V now becomes 0V and +2V becomes +4V.
In software you would compensate by subtracting 2V (half scale of A/D = 7FF) from the A/D result.






NOTE: The gain of the op-amp is 1.00475 so you will have to compensate for this also.

Regards,

Jacob