Nitrate nanomolar concentrations

Long-pathlength spectrometer. [Adapted from W. Yao. R. H. Byrne, artdR. D. Walerbury. Determination of Nanomolar Concentrations of Nitrite and Nitrate Using Long Path Length Absorbance Spectroscopy Environ. Sd. TechnoL 1998, 32,2646.]... 

Harrison, W. G., Harris, L., and Irwin, B. (1996). The kinetics ofnitrogen utihzation in the oceanic mixed layer Nitrate and ammonium interactions at nanomolar concentrations. Limnol. Oceanogr. 41, 16—32. 

Yao, W., Byrne, R., and Waterbury, R. (1998). Determination of nanomolar concentrations of nitrite and nitrate in natural waters using long path length absorbance spectroscopy. Environ. Sci. Technol. 32, 2646-2649. 

Lipschukz (2001) Report on the temporal variabihty of nitrate and ammonium (nanomolar) concentrations and uptake rates in the ohgotrophic upper layer. Nitrate uptake during the ohgotrophic periods does not strongly contribute to new production it is locally regenerated... 

Masserini, R. T., and Fanning, K. A. (2000). A sensor package for the simultaneous determination of nanomolar concentrations of nitrite, nitrate and ammonia in seawater by fluorescence detection. Mar. Chem. 68(4), 323—333. 

Garside, C. (1982). A chemiluminescent technique for the determination of nanomolar concentrations of nitrate and nitrite in seawater. Mar. Chem. 11, 159-167. 

In surface waters nutrient concentrations are often depleted below the detection limits of the routine colorimetric methods even when using the longest-pathlength spectrophotometer cells routinely available (10 cm). The accurate measurement of concentrations of these nutrients at nanomolar concentrations is now an important analytical goal. Therefore, in recent years, new methods for the analysis of nitrate and ammonium with lower detection limits have been developed based on chemiluminescence for nitrate, fluorescence or concentration of the standard colorimetric complex for ammonium, and preconcentration for DIP. Recently, the development of wave guides has opened up the possibiHty of using cell... 

Sensor for the simultaneous determination of nanomolar concentrations of nitrite, nitrate, and ammonia in... 

Van den Berg [131] used this technique to determine nanomolar levels of nitrate in seawater. Samples of seawater from the Menai Straits were filtered and nitrite present reacted with sulfanilamide and naphthyl-amine at pH 2.5. The pH was then adjusted to 8.4 with borate buffer, the solution de-aerated, and then subjected to absorptive cathodic stripping voltammetry. The concentration of dye was linearly related to the height of the reduction peak in the range 0.3-200 nM nitrate. The optimal concentrations of sulfanilamide and naphthyl-amine were 2 mM and 0.1 mM, respectively, at pH 2.5. The standard deviation of a determination of 4 nM nitrite was 2%. The detection was 0.3 nM for an adsorption time of 60 sec. The sensitivity of the method in seawater was the same as in fresh water. 

Consequently, at nanomolar signaling concentrations, the lifetime of NO is sufficient for it to reach sGC. The end-products of NO decomposition are nitrite (N02 ) and nitrate (NOs"). NO and reaction intermediates along the decomposition pathway can react with several intracellular molecules, but reactions... 

Compared with classical analytical methods such as gas chromatt raphy, HPLC, atomic absorption or mass spectrometry, the detection of pollutants by biosensors is generally less specific. These devices provide valuable information on a class of pollutants rather than a mere information about a specific compound, although the use of mutants that are resistant to specific pollutants can render them more selective. Biosensors provide valuable information about the real biological effects of the pollutants in a sample since phytotoxicity is determined from the measurement of electron transport activity, photocurrent or photosynthetic oxj en evolution. It is important to note that althoi the PSII complex is sensitive to various pollutants (herbicides, heavy metals, sulphites, nitrates, carbonates), its susceptibility to these compounds is highly variable, tanging from nanomolar to milhmolar concentrations. 

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