Determination Of Nitrate In Seawater Research Articles

Modification and validation of an analytical method for the simple determination of nitrate in seawater by reduction to nitrite with zinc powder

As copper-coated cadmium granules, which are recommended for use in the standard method for analyzing nitrate, are environmentally unfriendly and forbidden in some countries, an alternative method is required. To enhance the method for determining low nitrate concentration in seawater, the optimal conditions for reducing nitrate to nitrite using zinc powder were assessed in this study. The modified zinc method was optimal at an 0.8:1 (v/v) ratio of buffer solution (pH 8.5) (4 ml) to water sample (5 ml) with 50 mg of zinc powder and a standing time of 30 min. The nitrite was reacted with sulfanilamide and N-(1-Naphthyl)-ethylenediamine dihydrochloride after nitrate reduction, and spectrophotometrically quantified at 543 nm. This modified method was found to have a linear dynamic range of 0.1–7.0 μM, a low detection limit (0.1 μM), good intra-day and inter-day reproducibility (<5% relative standard deviation), high-efficiency reduction (>95%), and excellent accuracy in analysis of certified reference material (95% relative accuracy). The results obtained using the modified method agreed well with those obtained using the conventional cadmium column method. Overall, this alternative green chemistry method is a simplified procedure for determining nitrate in seawater with a high efficiency.

Field determination of nitrate in seawater using a novel on-line coppered cadmium column: A comparison study with the vanadium reduction method

Nitrate is the main form of dissolved inorganic nitrogen, playing an important role in both marine biogeochemical research and water environment management. In this work, the most commonly used coppered cadmium column was modified and a novel on-line Cu/Cd column with a spiral structure coupled with a de-bubbling device and syringe-type filter was developed. With the advantages of convenience, portability, stability, and high reduction efficiency, the interference of air bubbles in the column could easily be avoided. Based on the classic Griess reaction, a simple reverse flow injection system coupled with a novel Cu/Cd column and custom-made flow cell was established for the field spectrophotometric determination of nitrate in seawater. The effects of certain reaction parameters—including the reagent concentration, flow rate, length of the Cu/Cd column, and salinity—were investigated, optimized, and compared with pure water, with an approximate 9% increase in the sensitivity of seawater samples. This method exhibited a detection limit of 0.03 μmol/L, with a relative standard deviation of 0.6%, and the working range was 20 μmol/L before dilution. Compared to the referred vanadium reduction method based on the same flow system, the proposed method showed significant advantages including sensitivity and reproducibility. No significant difference was observed between the analytical seawater sample results obtained by the proposed and reference methods. Furthermore, the proposed method was validated by the first class of National Certified Reference Materials and successfully applied to the nitrate determination of Wenling coastal seawater (Zhejiang, China).

Comparative study on cadmium column reduction and UV-induced reduction for online determination of nitrate in seawater

An online detection system for nitrate in seawater was designed and set up based on flow injection analysis and spectrophotometry. We used this system to compare and study the two reduction methods for nitrate in seawater: cadmium column reduction method and UV light-induced reduction method. The cadmium column could reach the optimal reduction condition in 300 s while the UV light could reach the optimal reduction condition in 480 s. The two methods both had good linear relationship in the range of 5-500 μg/L. The reduction efficiency for Cd-column and UV light were 95% and 80% respectively under the same conditions. The detection limit was 2.5 μg/L for Cd-column reduction method and was 3.4 μg/L for UV-induced reduction method. The relative standard deviation (RSD) for the two methods were both less than 3%. The recovery rate for Cd-column reduction method and UV-induced reduction method were 98.22% and 100.83% respectively.

Determination of Nitrate in Seawater with Valve-Free Continuous Flow Analysis

Abstract A valve-free continuous flow method and its corresponding instrument were established, with only two multi-channel pump for delivering the sample and reagent, without any injection or solenoid valves and sample loop for selecting and adding the sample or reagent. Nitrate was reduced to nitrite with Cu-Cd reductant column, and then detected with spectrophotometric detector. The proposed method was suitable for determination of nitrate at normal level in most of estuary and coastal seawaters. With the optimum parameters, the linear range and detection limit were 5–180 μM and 0.27 μM, respectively. The nitrate samples (10 and 80 μM) were continually measured for 11 times, and the relative standard deviations were 1.4% and 1.3%, respectively. The recovery of real samples at different salinity was ranged from 99.4% to 106.1%. There were no significant differences in the analytical results between the proposed method and a reference method, i.e., flow injection analysis. In comparison with flow injection analysis, the method and instrument were less cost and easy to operate, and was suitable to be applied in general laboratories and field for continuous monitoring. The method was successfully applied to measure nitrate of seawater samples in Xiamen western harbor and underway monitor nitrate in the Jiulongjiang estuary.

Tandem electrochemical desalination-potentiometric nitrate sensing for seawater analysis.

We report on a methodology for the direct potentiometric determination of nitrate in seawater by in-line coupling to an electrochemical desalination module. A microfluidic custom-fabricated thin layer flat cell allows one to electrochemically reduce the chloride concentration of seawater more than 100-fold, from 600 mM down to ∼2.8 mM. The desalinator operates by the exhaustive electrochemical plating of the halides from the thin layer sample onto a silver element as silver chloride, which is coupled to the transfer of the counter cations across a permselective ion-exchange membrane to an outer solution. As a consequence of suppressing the major interference of an ion-exchanger based membrane, the 80 μL desalinated sample plug is passed to a potentiometric flow cell of 13 μL volume. The potentiometric sensor is composed of an all-solid-state nitrate selective electrode based on lipophilic carbon nanotubes (f-MWCNTs) as an ion-to-electron transducer (slope of -58.9 mV dec(-1), limit of detection of 5 × 10(-7) M, and response time of 5 s in batch mode) and a miniaturized reference electrode. Nitrate is successfully determined in desalinated seawater using ion chromatography as the reference method. It is anticipated that this concept may form an attractive platform for in situ environmental analysis of a variety of ions that normally suffer from interference by the high saline level of seawater.

Optimization of Zinc-Cadmium Reduction Method for Determination of Nitrate in Seawater

The linear of nitrate standard curve and blank values were ​​affected by many factors such as blank water quality, temperature, etc. The seawater determination of nitrate optimization methods in this paper based on the GB "marine monitoring specification (seawater analysis)"GB12763.4-2007. It indicated that doubly distilled water with excellent pure sodium chloride for preparation of artificial seawater produce a good linear of standard curve and lowest blank value at 20 °C -25 °C.

Onboard Determination of Submicromolar Nitrate in Seawater by Anion-Exchange Chromatography with Lithium Chloride Eluent

Ion-exchange chromatography using a high-capacity anion exchanger with UV detection was applied to the determination of nitrate in seawater. Major ions in seawater samples did not affect the peak shape and the retention time of the nitrate when an alkaline metal cation-chloride solution was used as an eluent at high concentrations (0.5-2 mol/l). At a wavelength of 220 nm, the peak of bromide was very small because of low absorption, while its separation from the nitrate peak was good at high concentrations. Among the eluents tested, lithium chloride gave the best separation of nitrate from bromide. It was estimated that the lithium ion had the least potential for ion-pair formation with nitrate, and its retention time was prolonged compared with the retention times when using other cations; with bromide and nitrite, such an effect was not observed. The results of shipboard seawater nitrate determination by our method in the South Pacific Ocean and Antarctic Sea showed good agreement with those by the conventional photometric method using continuous flow.

A simplified resorcinol method for direct spectrophotometric determination of nitrate in seawater

A direct, spectrophotometric method has been adapted for quantitative determination of nitrate concentrations in seawater. The method is based on nitration of resorcinol in acidified seawater, resulting in a color product. The absorption spectrum obtained for the reaction product shows a maximum absorption at 505 nm, with a molar absorptivity of 1.7 × 10 4 L mol − 1 cm − 1 . This method has a detection limit of 0.5 μM and is linear up to 400 μM for nitrate. The advantage of this method is that all reagents are in aqueous solutions without involving cadmium granules as a heterogeneous reactant, as in conventional methods, and therefore is simple to implement. Application of the resorcinol to seawater analysis demonstrated that the results obtained are in good agreement with the conventional approach involving the reduction of nitrate by cadmium followed by diazotization.

Determination of nitrate in seawater by capillary zone electrophoresis with chloride-induced sample self-stacking

A capillary zone electrophoresis (CZE) method was established to determine low concentration nitrate which was online preconcentrated with chloride-induced leading-type sample self-stacking for seawater samples. The sample self-stacking was based on transient isotachophoresis in which chloride served as leading ion, and dihydrogenphosphate in the background electrolyte (0.1 M phosphate) as the terminating one. Due to the small mobility difference between nitrate and chloride, the isotachophoresis time was so long that nitrate could not separate from the rear sharp boundary between chloride and the background electrolyte (BGE) when it migrated to the detection window. A zwitterionic surfactant, 3-( N, N-dimethyldodecylammonio)propane sulfonate was added to the BGE to enlarge the mobility difference for its selective interaction with anions. Thus, a highly conductive sample could be injected in a large volume with about fourfold sensitivity enhancement compared to that of field amplification sample stacking in which nitrate was dissolved in pure water. The relative standard deviations ( n=5) of migration time, peak area, peak height were 0.1, 3.0, 1.5%, respectively. The limit of detection ( S/ N=3) for nitrate was 35 μg/l in seawater samples with relatively low concentration BGE (0.1 M sodium phosphate, pH 6.2). The overall procedure consisting of online preconcentration and separation was as simple as routine CZE except for a slightly longer sample injection time (3–4 min).

Determination of nitrate in seawater: Nitrate to nitrite reduction with copper-cadmium alloy

Determination of nitrate in seawater first requires its reduction to nitrite. Construction of a reductor column for use during continuous flow analysis at sea is described. Novel use is made of an alloy of cadmium and copper ( 50 50 w w ) crushed to between 500 and 350 μm. Its performance is similar to that of the cadmium wire type of reductor but offers advantages of easier preparation and control of reductor volume.

Determination of Nitrate Ion in Marine Biotopes with High Nitrate Content by Ultraviolet Spectrophotometry

AbstractA simple and rapid method for the determination of nitrate in seawater of high nitrate content (&gt; 1 ppm) is proposed.The absorption of the nitrate ion is measured at 210 and 220 mμ. The sample is treated with a measured quantity of hydrochloric acid to eliminate the carbonate and bicarbonate interferences and measured against a nitrate free blank prepared by reduction of the nitrate to ammonia with Raney nickel. The addition of HCl permits also storage of the sample without special precautions and the use of the blank eliminates the most serious of the interferences (bromide) expected in sea‐water. The interference of organic matter limits however the applicability of the method to concentrations higher than 1 ppm.

The determination of nitrate in sea-water : Morris, A. W. and J. P. Riley, 1963. Analy. Chim. Acta, 29 (3): 272–279

The determination of nitrate in sea-water : Morris, A. W. and J. P. Riley, 1963. Analy. Chim. Acta, 29 (3): 272–279