This chart represents the NADP/NTN database values for NO3 compared to those same values adjusted with Robin's algorithm.

The procedure to adjust NO3 is as follows: 
Model equations of the lid seal concentration for the conservative ions. 
Volume (V) is in milliliters. 'P' is pH. Concentration is in mg/l. 

To adjust NADP data before 1994, subtract this result from the lab concentration. NO3 (9.92/V) * (1 - exp(-.00701*V))