Recent progress in sensing nitrate, nitrite, phosphate, and ammonium in aquatic environment

Aquatic ecosystems respond variably to nutrient enrichment and altered nutrient ratios, along a continuum from fresh water through estuarine, coastal, and marine systems. Although phosphorus is considered the limiting nutrient for phytoplankton production in freshwater systems, the effects of atmospheric nitrogen and its contribution to acidification of fresh waters can be detrimental. Within the estuarine to coastal continuum, multiple nutrient limitations occur among nitrogen, phosphorus, and silicon along the salinity gradient and by season, but nitrogen is generally considered the primary limiting nutrient for phytoplankton biomass accumulation. There are well-established, but nonlinear, positive relationships among nitrogen and phosphorus flux, phytoplankton primary production, and fisheries yield. There are thresholds, however, where the load of nutrients to estuarine, coastal and marine systems exceeds the capacity for assimilation of nutrient-enhanced production, and water-quality degradation occurs. Impacts can include noxious and toxic algal blooms, increased turbidity with a subsequent loss of submerged aquatic vegetation, oxygen deficiency, disruption of ecosystem functioning, loss of habitat, loss of biodiversity, shifts in food webs, and loss of harvestable fisheries.

In this article, we report the simultaneous determination cholesterol (CL), ascorbic (AA) acid and uric acid (UA) at a carbon paste electrode (CPE) modified with copper oxide decorated reduced graphene (CuO-rGR), with 1-methyl-3-octylimidazolium tetrafluoroborate (1M3OIDTFB) as a binder. The electrode, CuO-rGR/1M3OIDTFB/CPE, showed remarkable sensitivities towards the determination of the analytes, and well defined and clearly separated oxidation peaks were obtained during their simultaneous analysis in a buffer solution at pH 7.4. The differences observed between their peaks potentials are as follows: 430 mV (between CL and AA), 270 mV (between AA and UA) and 700 mV (between CL and UA). The morphologies and structure properties of the CuO-rGR were investigated by FESEMD and EDAX methods. The CuO-rGR/1M3OIDTFB/CPE displayed linear response in the concentration ranges 0.04-300.0 μM, 0.04-240.0 μM and 0.4-400.0 μM for CL, AA and UA with the detection limits 9.0 nM, 9.0 nM and 0.08 μM, respectively. The CuO-rGR/1M3OIDTFB/CPE displayed high performance for the determination of CL, AA and UA in real samples.

Nanoparticles can display four unique advantages over macroelectrodes when used for electroanalysis: enhancement of mass transport, catalysis, high effective surface area and control over electrode microenvironment. Therefore, much work has been carried out into their formation, characterisation and employment for the detection of many electroactive species. This paper aims to give an overview of the investigations carried out in this field. Particular attention is paid to examples of the advantages and disadvantages nanoparticles show when compared to macroelectrodes and the advantages of one nanoparticle modification over another. Most work has been carried out using gold, silver and platinum metals. However, iron, nickel and copper are also reviewed with some examples of other metals such as iridium, ruthenium, cobalt, chromium and palladium. Some bimetallic nanoparticle modifications are also mentioned because they can cause unique catalysis through the mixing of the properties of both metals.