Nitrogenous species, such as ammonia, nitrite, nitrate, hydroxylamine (NH2OH) and nitrous oxide (N2O), are recycling through microbial processes in the hydrosphere.1-3 NH2OH has been identified as an intermediate in the nitrogen cycles, such as the oxidation of ammonia to nitrite and the reduction of nitrite to ammonia by several microorganisms in aquatic and sedimentary systems. 4,5 Furthermore, NH2OH is often described as an intermediate for producing N2O. N2O is one of the greenhouse gases, and is also associated with the reduction of ozone in the stratosphere. Hence, NH2OH is an important nitrogen species not only for understanding the nitrogen cycle, but also for clarifying the mechanism of N2O production.It has been reported that millimolar solutions of NH2OH are stable for several hours at pH 4.0, but only for 60 min at pH 7.8 in the presence of air. 6,7 Thus, the direct determination of NH2OH is difficult in environmental water because of its low concentration and instability. Several methods, such as spectrophotometric methods 6,9-11 and a titrimetric method 12 for the determination of NH2OH, have been reported. The former method is based on the combination of the oxidation of NH2OH to nitrite with iodine and the usual Griess-Romijin method. This method, however, is subject to interference from nitrite. 13The latter method is based on the oxidation of NH2OH using ferric ammonium sulfate with a copper sulfate catalyst. In this method, Fe(III) was reduced by NH2OH and the resultant Fe(II) was titrated with potassium dichromate. This method is applicable in the millimolar range. In general, these methods were employed only in media containing a relatively high concentration of NH2OH. On the other hand, Marta et al. developed a gas chromatographic method for the determination of nanomolar concentrations of NH2OH by its oxidation to N2O using Fe(III) ions.14 However, the yield for the conversion of NH2OH to N2O by this method was 50%.In a previous paper, 13 we reported the spectrophotometric determination for NH2OH in environmental water samples. The interference from nitrite in the water sample described above was solved by removing the resultant azo dye from nitrite using a Sep-Pak C18 cartridge prior to the analysis of NH2OH. Although this method was available for environmental water samples from fresh-water to seawater, the procedure was very tedious. In this paper, we propose a new and simple method for the determination of nanomolar NH2OH in fresh-water samples by its oxidation to nitrous oxide using hypochlorite as an oxidizing agent. The N2O produced in this manner was subsequently measured by using a gas chromatograph with an electron-capture detector (ECD). Experimental Reagent and apparatusReagent solutions were prepared with high-purity water from a Millipore Milli-Q purification system. A standard NH2OH solution (500 mgN L -1 ) was prepared by dissolving 0.2481 g of hydroxylammonium chloride in 100 mL of water deoxidated with nitrogen gas. It was fleshly prepared for each analysis. A hypochlorit...
Dissolved sulfide in environmental water, which forms HS -rather than H 2 S above pH 7, is produced from microbial sulfate reduction. It is highly toxic to most organisms, and stable only in anoxic aqueous environments, which are linked with water pollution, especially in closed water areas, such as lakes. 1 Therefore, the determination of dissolved sulfide is important for understanding the oxidation-reduction level and water quality in environmental water locations.The Methylene Blue spectrophotometric method is widely used for the determination of dissolved sulfide in water.2-4 Dissolved sulfide in fjord water samples was determined by the Methylene Blue method to clarify its behavior 5 , and the chemical interactions between dissolved sulfide and heavy metals. 6,7 This method was also applied to anoxic seawater samples. 8,9 However, there are serious problems concerning sample collection, the storage and preservation of water samples, and the determination procedure, because dissolved sulfide in water is rapidly oxidized in contact with air and readily escapes as gaseous hydrogen sulfide into the air. Therefore, it is recommended that, immediately after sample collection, dissolved sulfide in a water sample is fixed as zinc sulfide using a zinc acetate solution at sampling sites, and then determined spectrophotometrically in a laboratory. 2,3 However, this method requires one to carry a number of voluminous water samples containing the zinc sulfide precipitate back to the laboratory from the sampling sites. It appears to be advantageous and more convenient to make the sample size smaller for the sake of easy carriage and storage of samples in field works.We have already reported on simple and rapid preconcentration methods for iron (II) 10 , manganese(II) 11 , and both thiosulfate and sulfite 12 in water using a SepPak C18 cartridge packed with C18-bonded silica, and that for phosphate 13 in water using a small column packed with zirconium-loaded activated carbon. These methods were successfully applied to environmental water samples as an in situ one, which were available at sampling sites. We have also developed a simple field determination of dissolved sulfide in environmental water samples using a lead-loaded chelating resin column. 14 Although this method was available for an in situ determination, its sensitivity and determination limit (0.5 mg sulfide-S/l) were not adequate for dissolved sulfide concentrations in environmental water samples, because this method was based on the length of a colored layer (lead sulfide layer) in a column proportional to the dissolved sulfide concentration in water.This paper describes a simple and rapid method for the in situ collection and preconcentration of dissolved sulfide in environmental waters. This method is based on the solid-phase extraction of Methylene Blue converted from sulfide, with Sep-Pak C18 cartridges, followed by a spectrophotometric determination. The Methylene Blue formation was based on the reaction of sulfide, iron(III) chloride, and N,N-dimet...
A simple and rapid in situ preconcentration method for the determination of phosphate in environmental waters has been developed for field analysis. This method is based on solid-phase extraction on a zirconium-loaded Sep-Pack Accell CM cartridge (Zr-SP) and is applicable to studies in which sampling is performed by use of a graduated syringe to prevent contamination and to ensure easy operation at sampling sites. The Zr-SP cartridge was prepared by passing 0.1 mol L(-1) zirconium solution through a Sep-Pak Accell CM cartridge, packed with cation exchange sorbent based on a silica matrix. The adsorption of phosphate and its desorption depend only on the pH of the solution. A water sample containing phosphate was adjusted to pH 2 and passed through the Zr-SP cartridge to collect it. The retained phosphate was quantitatively eluted with 0.5 mol L(-1) sodium hydroxide solution. The phosphate retained in the Zr-SP cartridge was stable for at least one month. The established preconcentration method was successfully applied to brackish lake waters to investigate seasonal changes in the distribution and behavior of phosphate in a brackish lake.
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