Nitrate anion sensors: Their applications and a case study of their status in waste water from selected areas of coastal guyana via a spectrophotometric method

Abstract

It is not an easy task to synthesize nitrate anion selective sensors considering that a nitrate anion is trigonally shaped, heavy solvated, has weak basicity and is difficult to form robust hydrogen bonds with ligands. In addition, anion coordination is a difficult aspect of supramolecular chemistry. Many receptors reported to date are halide selective, but few are nitrate selective. Nitrate anion receptors synthesized to date include polyammonium, amide and urea receptors amongst others. In one instance the association constant of a nitrate receptor showing the highest degree of complexation is reported to be Ka = 110M-1 in 50% DMSOd6/ CDCl3 and 20M-1 in 100% DMSO-d6 respectively. Globally, the presence of nitrate anions in water beyond the threshold limit can be deleterious to both flora and fauna life. Guyana’s waste and domestic water needs monitoring to assess the concentration of toxic anions and cations. High levels of nitrate anions beyond the threshold limit can induce the “blue baby” syndrome amongst other effects. One aspect of this chapter focuses on the determination of nitrate anion concentration from twelve selected areas of coastal Guyana using an ultraviolet spectrophotometric method. Areas monitored in Guyana were 58 Livelihood Village, Rose Hall Town, Skeldon GUYSUCO Estate, Good Hope, Ogle, Stabroek, Parika, Supenaam, Spring Garden in one instance. In another research endeavor, Georgetown Seawall Kingston, LBI, GUYSUCO Estate and the Canje river water at 20 and 40ft from the effluent were monitored. The results showed that the concentrations of nitrates were not as high as expected and are below the internationally accepted threshold values. In the first instance, the average concentration was measured to be 0.030 mg/L (± 0.039 mg/L), 0.064 mg/L (± 0.00292 mg/L), 0.203 mg/L (± 0.00738 mg/L), 1.772 mg/L (± 0.00 mg/L), 2.363 mg/L (± 0.839mg/L), 0.33 mg/L (± 0.156 mg/L), 0.168 mg/L (± 0.043mg/L), 0.142 mg/L (± 0.043 mg/L) and 0.178 mg/L (± 0.039 mg/L) respectively. In the second instance the measured results were 0.45 mg/L (± 0.039 mg/L), 0.01 mg/L (± 0.0033mg/L) and 0.015 mg/L (± 0.0023 mg/L) NO3-for Georgetown Seawall (Kingston area), LBI GUYSUCO Estate and the Canje river, 20 feet from the effluent respectively. The results were accepted at the 95% confidence level using statistical analyses. The US public Health Service designated the safe limit for nitrate in water as 45mg/L. The applicable range of concentrations using the above method is 0.1-2 mg/L NO3-. A maximum level of 45 mg/L is established as worldwide guidance for nitrate concentration in water. In Europe, the maximum permitted levels of nitrate in potable water is 50.0 mg/L, while in the US-EPA has established a guideline for the maximum level of nitrate-nitrogen of 10 mg/L. It can safely be informed that the twelve selected areas of coastal Guyana chosen are not polluted with anions. In an effort to improve water quality, the Government of Guyana has embarked on the construction of sand filtration and water treatment plants along the inhabited coastland of Guyana.