Inorganic salts diluted in water probed by Raman spectrometry: Data processing and performance evaluation

The paper reports on a methodology for the determination, by means of Raman spectrometry, of the concentration of inorganic salts dissolved in aqueous solutions. This procedure is then applied to nitrate solutions with a varying content from 0 to 100 mM (mmol/l). For this we exploit the concentration dependence of the Raman peak lying at 1047 cm−1 specific to the NO3− anion. Different signal processing and normalization methods are used and compared to deduce the most reliable and robust calibration. Then cross-validations are done using the “leave-one-out” method to validate the prediction models. Several figures of merit such as sensitivity, signal to noise ratio, limits of detection and quantification are calculated to estimate the efficiency of our methodology for nitrate solutions. Various sources of uncertainties are considered and evaluated according to the ISO GUM and the standard uncertainty of the concentration is then calculated.