Nitrates monitoring by UV-vis spectral analysis

The monitoring of nitrates using the second derivative of UV-vis spectra has been tested for a large set of samples (≈900) covering a large range of freshwater environments in the Moselle River drainage basin (headwater streams in the Vosges Mountains; tributaries, including the Madon River and Vologne River; and waters of various origins exposed to anthropogenic activities in villages). Satisfactory linear correlations (coefficient of determination > 0.74) were obtained between nitrate concentrations (measured by ion chromatography with a conductivity detector) and the maxima of the second derivative in the UV range for sets of mesotrophic and eutrophic samples. The meaningfulness of the linear regressions was verified by applying a Fisher-Snedecor test using a level of confidence of 0.05. The quality of the correlation decreased when the samples came from oligotrophic environments due to the limited sensitivity of the ion chromatography technique. UV-vis spectroscopy combined with the second derivative method appears to be a good alternative for monitoring nitrate-related eutrophication in the laboratory as well as in situ using submersible spectrophotometers.