The nitrate concentration in an industrial effluent is determined using a nitrate ion selective electrode.
Standards and samples are diluted 20-fold with 0.100 K2SO4 to maintain consatnt ionic strength.
Nitrate standards of 0.00500M and 0.0100M give potential readings of -108.6 mV and -125.3 mV respectively.
The sample gave a reading of -118.5 mV. What is the nitrate concentration in this sample?