Hello,
The TIA of the LMP91000 is a programmable TIA and its programmable resitances are precise at 5%. In the datasheet the 5% is releated to that precision.
Regarding the measurements you have done wiht the SPIO4, can you please provide me with the configuration of the LMP91000 (its internal registers) ?
The comparison with a lab potentiostat makes sense only if you are sure that both systems: the one based on the LMP91000EVM+SPIO4 and the lab potentiostat are working in the same conditions.
Do you know if the lab potentiostat is making any averages? If so you should make the same operation with the data acquired by the SPIO4. The SPIO4 + LMP91000EVm doesn't have any filter to rejuect the grid frequency, maybe the lab potentiostat has that filter.
regards,
Domenico