Marine Science Faculty Publications


Determination of Nanomolar Concentrations of Nitrite and Nitrate in Natural Waters Using Long Path Length Absorbance Spectroscopy

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The concentrations of nitrite and nitrate in many natural waters are below the detection limits of conventional colorimetric analysis. A liquid core waveguide (LCW) has been used to extend the sensitivity of conventional colorimetric nitrite and nitrate determinations by more than an order of magnitude. Long path length absorbance spectroscopy (LPAS) with a 4.5 m path length LCW made of Teflon AF-2400 provides detection limits for NO2- and NO3- equal to 0.5 and 1.5 nM, respectively. The absorbance response of the LPAS system varies linearly with concentration. Calculations of azo dye molar absorbance using LPAS observations at nanomolar concentrations are in excellent agreement with molar absorbance results obtained with conventional measurement systems at much higher concentrations. For 1 nM NO2- and NO3- concentration differences, the 4.5 m path length LCW used in this work produces absorbance differences on the order of 0.02. No significant changes in the behavior of the LPAS system have been observed for periods of 6 month and more. The system is simple, rugged, and amenable to field studies.

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Environmental Science & Technology, v. 32, issue 17, p. 2646-2649