System and method for determining aqueous nitrate concentration in solution containing dissolved organic carbon

A method for determining a concentration of nitrate in a water sample collected from soil at a given site, said water sample also contains an unknown composition and unknown concentration of Dissolved Organic Carbon (DOC), the method comprising:

• a. during an offline stage:
• collecting a testing sample from the site;
• analyzing the testing sample to determine a first wavelength in which a light absorbance by the testing sample is correlated to the concentration level of the DOC in the testing sample;
• further analyzing the testing sample to determine a second wavelength in which a light absorbance by the testing sample is correlated to the concentration level of the nitrate in the testing sample;
• based on the above two-step offline analysis, creating a multivariate polynomial calibration equation for use during a real-time stage analysis;
• and
• b. during a real-time stage analysis:
• collecting a real-time water sample from the site's soil;
• impinging on the real-time sample light in said first wavelength, measuring the real-time sample's absorbance, and recording the measured absorbance as a first absorbance value;
• impinging on the real-time sample light in said second wavelength, measuring the real-time sample's absorbance, and recording the measured absorbance as a second absorbance value;
• and
• substituting in said calibration equation the first absorbance value and the second absorbance value, or values relative thereon, and calculating to determine the nitrate concentration in the real-time sample.