A sensor package for the simultaneous determination of nanomolar concentrations of nitrite, nitrate, and ammonia in seawater by fluorescence detection |
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| Authors: | Robert T Masserini Jr Kent A Fanning |
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| Institution: | University of South Florida, Department of Marine Science, 140 7th Ave. South, St. Petersburg, FL 33701, USA |
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| Abstract: | A fluorescence-based chemistry has been developed for the detection of nitrite and nitrate (as excess nitrite following reduction of nitrate to nitrite). Detection limits are 4.6 and 6.9 nM, respectively. The technique capitalizes on the triple bond between the two nitrogen atoms within the diazonium ion formed via the well-known reaction between an acidified nitrite sample and an aromatic primary amine. Fluorescence of π-electrons within this bond allows this reaction to be probed with standard fluorescence spectroscopy. Reverse Flow Injection Analysis (rFIA) is used to correct for background fluorescence from leachates and naturally occurring dissolved organic matter (DOM). Comparisons of samples analyzed for nitrite with this technique and with a highly-sensitive chemiluminescent method Braman, R.S., Hendrix, S.A., 1989. Nanogram nitrite and nitrate determination in environmental and biological materials by vanadium (III) reduction with chemiluminescence detection. Analytical Chemistry, 61 (24) 2716–2718] showed excellent agreement between the two methods (slope=0.9996 and r2=0.9956). These fluorescent nitrite and nitrate + nitrite chemistries were coupled in a sensor package with a modified version of a fluorescent ammonia chemistry Jones, R.D., 1991. An improved fluorescence method for the determination of nanomolar concentrations of ammonia in natural waters, Limnology and Oceanography. 36(4) 814–819], which also has a nanomolar detection limit. The throughput rate of the fully automated three-channel instrumentation is 18 samples per hour. A field experiment demonstrated the capability of the nutrient sensor package to determine horizontal gradients in nitrate, nitrite, and ammonia in oligotrophic surface waters. |
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| Keywords: | nutrients nitrate nitrite ammonia fluorescence |
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