Nitrate and nitrite detection in water environment by UV absorption spectroscopy—application to fish farm samples

Abstract The detection of NO 3 − and NO 2 − in NaNO 3 , NaNO 2 solutions and fish farm water samples was carried out in the 265–365 nm UV range. The equipment used was an optoelectronic platform of 200 × 400 × 250 mm 3 , composed of electroluminescent diodes. The detector had a narrow emission spectrum of 12 nm at full width at half maximum (FWHM), a long-path optical cell, and a broadband photodiode. An optical emission spectrometer was employed as an alternative detector. Both detectors were involved in the calibration procedure of the platform for NO 3 − and NO 2 − quantification in liquids in the concentration range of 0.3–365 mg l −1 . In the case of the photodiode, the limit of detection of NO 3 − was 2.2 ± 0.04 mg l −1 at 295 nm, and for NO 2 − , it was 0.3 ± 0.007 mg l −1 at 340 nm. These values represent improvements of 1.4 mg l −1 and 2.3 mg l −1 , respectively, compared to those provided by a UV–Vis spectrophotometer calibrated at the NO 3 − and NO 2 − maximum absorption wavelengths of 303 and 354 nm. Measurements of 27.5 ± 3.3 mg l −1 NO 3 − at 310 nm and 5 ± 0.12 mg l −1 NO 2 − at 340 nm were obtained from fish farm water samples. These overcame the issue that UV–Vis spectrophotometric data were unquantifiable due to poor sensitivity and interference from other ions.