Cadmium Reduction Research Articles

Comparison of cadmium and enzyme-catalyzed nitrate reduction for determination of NO 2−/NO 3− in breath condensate

Background: Analysis of NO 2 −/NO 3 − in expired breath condensate (EBC) has been proposed as a marker of inflammation in various lung diseases. Methods: NO 2 − and total NO 3 −/NO 2 − concentrations were determined in EBC collected from healthy and asthmatic subjects. The NO 3 − was first reduced to NO 2 −, and total NO 2 − was detected by colorimetric Griess reaction. Two methods of NO 3 − reduction were compared. To reduce NO 3 −, cadmium (600 μl EBC-macromethod) and enzyme–NADPH–nitrate reductase (60 μl EBC-micromethod) were used. Results: Macromethod: Mean NO 2 − concentrations in EBC were 1.64±0.24 μmol/l in healthy subjects and 0.42±0.17 μmol/l in asthmatic patients. Mean total NO 2 −/NO 3 − levels were 3.64±0.43 μmol/l in healthy subjects and 3.27±0.34 μmol/l in asthmatic. Micromethod: NO 2 − level: 1.69±0.23 μmol/l in healthy subjects and 0.53±0.21 μmol/l in asthmatics. Total NO 2 −/NO 3 − levels: 3.56±0.37 μmol/l in healthy subjects and 3.57±1.17 μmol/l in asthmatics. Variability index was 27% and 6% for macro- and micromethod, respectively. Recovery of NO 3 − added to EBC was 100% for enzymatic and almost 88% for cadmium reduction. There was no correlation between total NO 2 −/NO 3 − levels determined by macro- and micromethod. Conclusions: We recommend enzymatic reduction as a better method for NO 3 − determination in EBC.

Removal of cadmium from simulated wastewaters by electrodeposition on spiral wound steel electrode

The electrowinning of cadmium from dilute sulphate solutions was studied by voltammetry and chronopotentiometry in a conventional three-electrode cell using a rotating glassy carbon and spiral wound steel electrodes. The polarization curves provided valuable information about the electrolytic cadmium reduction as well as of the respective current densities. The results of the recovery of cadmium by using a flow-by cell with spiral wound steel high-surface-area cathode were also described. The cell was operated in a continuous recirculated batch process. This reaction system was found to be extremely effective in reducing metal concentrations to the permissible range. Cadmium recovery of 30% at 250 μA cm −2 increases sharply to 99.95% at 400 μA cm −2.

N-Nitroso Compound Precursors in some Nigerian Forage Crops

Primary and secondary amine contents of some dried Nigerian forages were analyzed as their sulphonamides by gas chromatography interfaced with a chemiluminescence detector-Thermal Energy Analyzer modified for use in nitrogen mode. Both nitrate and nitrite were analyzed spectrophotometrically using an automated dual channel continuous flow nitrate-nitrate analyzer as nitrite following cadmium reduction of nitrate to nitrite and diazotization of nitrite with sulphanilamide, and coupling with N-(1-naphythyl) ethylenediamine. Secondary amines detected in the forage were diethylamine, dimethylamine, methylbenzylamine, piperidine, methylamine, while primary amines found include n-butylamine, ethylamine, methylamine, isopentylamine and propylamine. Total secondary amines were highest in Urena lobeta (92.7 ppm), but lowest in Dichrostachys cinera (5.6 ppm), while total primary amines were also highest in Urena lobeta (94.7ppm) but lowest in Rottboellia exaltata (8.4 ppm). Only trace amounts of nitrite were detectable in some samples. The toxicological relevance of these findings are discussed with respect to potential endogenous formation of hepatotoxic, mutagenic and carcinogenic n-nitroso compounds in animals, and the consequences of this phenomenon on animal health and production. Keywords: N-nitroso precursors, forages, Nigeria Trop. Vet. Vol. 21 (2) 1-8 (2003)

Miniature flow injection analyser for laboratory, shipboard and in situ monitoring of nitrate in estuarine and coastal waters

A miniature, submersible flow injection analyser, with solid-state spectrophotometric detection, for the in situ determination of nitrate is described. It utilises the standard laboratory chemistry of cadmium reduction followed by diazotisation. The detection limit was 2.8 μg l −1 N and the linear range could be varied from 2.8 to 100 μg l −1 N up to 100–2000 μg l −1 N to suit local environmental conditions. The versatility of the instrument is demonstrated by results from laboratory, shipboard (North Sea IMPACT Cruise) and in situ (Tamar Estuary, UK) deployments. They show the excellent temporal and spatial resolution that can be achieved for studying dynamic processes in estuarine and coastal waters. The results acquired during the IMPACT Cruise map the transport of nitrate from the Humber Estuary into the North Sea and show that nitrate uptake was more pronounced in areas of shallow and clear waters (Dogger Bank) than in the coastal mixing zone with higher suspended solids. A key feature of the analyser is its portability and ease of deployment due to the small size and weight and low buoyancy. Accuracy was assessed by participation in an international intercomparison exercise and the results were within the assigned tolerance interval of the consensus mean ( Z<2).

Flow injection chemiluminescent method for the successive determination of l-cysteine and l-cystine using photogenerated tris(2,2′-bipyridyl) ruthenium (III)

Flow injection configurations were developed for the individual determination of l-cysteine and l-cystine and for the mixture of both analytes. The method is based on the reaction of l-cysteine with tris(2,2′-bipyridyl) ruthenium (II) and peroxydisulphate under UV irradiation to produce chemiluminescence. Cystine is determined after reduction to cysteine in a copper-coated cadmium reductor mini-column in the flow system. The inclusion of a selection valve in the configuration allows the successive determination of the two analytes. Calibration was linear between 2×10 −6 and 5×10 −4 mol l −1 for cysteine and between 1×10 −6 and 2×10 −4 mol l −1 for cystine. When applied to pharmaceutical formulations, the procedure was free from interferences from common excipients. The results obtained for the assay of commercial formulations compared well with those obtained by an official method and demonstrated good accuracy and precision.

COMPARISON OF METHODOLOGIES FOR NITRATE DETERMINATION IN PLANTS AND SOILS

ABSTRACT Several procedures have been described for the determination of nitrate by biological reduction, cadmium reduction, and salicylic acid electrophilic substitution. However, all are subject to interference by constituents of soil and plants. The aim of this work is to compare the results obtained using these methods with those obtained by ion chromatography. Because most of the interferences to which these methods are subject are due to organic matter, three pretreatments to reduce the presence of organic matter in the sample extracts were compared: 1 – adding activated charcoal; 2 – filtering through a 0.45 μm filter; and 3 – ultra-filtering through a 10 kDa membrane. A method and respective pretreatment were considered acceptable for measurement of nitrate in a particular soil or plant extract if: (i) nitrate added to the extraction medium used (without the soil or the plant material) was quantitatively recovered, and an acceptable reference curve could be established; (ii) between 95% and 105% of the nitrate added to the sample was recovered; and (iii) replicates agreed within 10%. Method recommendation for future analysis was based on: 1 – simplicity; 2 – accuracy; 3 – interferences; 4 – equipment needed; and 5 – cost of analysis. Application of these criteria to the results indicated that the biological reduction of nitrate with nitrate reductase (NR) from E. coli is the most suitable method for nitrate determination in laboratories that are not equipped with an ion chromatograph.

A simple simultaneous flow injection method based on phosphomolybdenum chemistry for nitrate and nitrite determinations in water and fish samples

A direct spectrophotometric flow injection method for the simultaneous determination of nitrite and nitrate has been developed. The method is based on the oxidation of a phosphomolybdenum blue complex by the addition of nitrite and the decrease in absorbance of the blue complex is monitored at 820 nm. The injected sample is split into two segments. One of the streams was directly reacted with the above reagent and detected as nitrite. The other stream was passed through a copperised cadmium reductor column where reduction of nitrate to nitrite occurs, and the sample was then mixed with the reagent and passed through the cell of the spectrophotometer to be detected as nitrite plus nitrate. The conditions for the flow injection manifold parameters were optimised by experimental design and the concentration of nitrite and nitrate was determined in the linear range from 0.05 to 1.15 μg ml −1 nitrite and 0.06 to 1.6 μg ml −1 nitrate with a detection limit of 0.01 μg ml −1 for nitrite and 0.025 μg ml −1 for nitrate. The method is suitable for the simultaneous determination of nitrite and nitrate in fish and water samples with a sampling rate of 25±2 sample per hour.

Cadmium removal from water using thiolactic acid-modified titanium dioxide nanoparticles

This study investigated the use of titanium dioxide (TiO 2) nanoparticles to remove aqueous cadmium from simulated wastewaters. Nanosized (45 Å) colloids of anatase TiO 2 were synthesized through the controlled hydrolysis of TiCl 4 and their surfaces modified with the bidental chelating agent thiolactic acid (TLA). Colloids were introduced into 65 ppm cadmium-laden waters, and the suspensions were purged aerobically, anoxically with an inert gas, or by a sequential aerobic/anoxic purge. Suspensions were illuminated with 253.7 nm light. In each experiment, samples were taken from the reactor, filtered, and the filtrates analyzed by atomic absorption spectroscopy for residual cadmium. Results from the aerobic experiments exhibited minimal (approximately 10%) removal of the cadmium from solution and no reduction of the metal on either the modified or the unmodified colloid. Anoxic results were more promising, showing no cadmium reduction on the unmodified colloid but a 40% adsorption and reduction (from a +2 valence state to elemental cadmium as determined by methyl viologen tests) of cadmium on TLA-modified colloid in the presence of light. Results from the mixed atmospheric conditions fared the best and demonstrated that in the absence of light, approximately 20% of aqueous cadmium was sorbed to the modified colloid via a Freundlich adsorption isotherm. Upon illumination, greater than 90% of cadmium was removed by both adsorption and reduction processes onto the TLA-modified TiO 2. These removal and reduction processes were catalytic in nature. Results from this study are significant because to date, no other research in the literature has been able to accomplish cadmium removal and reduction using TiO 2.

Second derivative UV absorbance analysis to monitor nitrate-reduction by bacteria in most probable number determinations

Heterotrophic and autotrophic nitrate-reducing bacteria (NRB) play important roles in many environments. These bacteria are often enumerated by most probable number (MPN) methods. Measuring NO 3 − depletion in the MPN cultures is the definitive way to determine the presence of NRB. Media used for MPN determinations of NRB in oil field waters usually contain high Cl − concentrations, matching those in the water samples. Many methods for measuring NO 3 − concentrations, such as ion chromatography (IC), cadmium reduction and ion electrode methods, are adversely affected by high concentrations of Cl − and organic compounds. A second derivative UV absorbance method proved to be a fast and reliable means for measuring NO 3 − depletion in MPN media used for enumerating autotrophic and heterotrophic NRB, without interferences from Cl − or the organic components in the latter medium. The MPN results for heterotrophic NRB determined by the second derivative UV absorbance agreed well with those determined by the production of nitrous oxide, and were often higher than those determined by measuring nitrate depletion by the diphenylamine spot test.

Corn leaf nitrate reductase--a nontoxic alternative to cadmium for photometric nitrate determinations in water samples by air-segmented continuous-flow analysis.

Development, characterization, and operational details of an enzymatic, air-segmented continuous-flow analytical method for colorimetric determination of nitrate + nitrite in natural-water samples is described. This method is similar to U.S. Environmental Protection Agency method 353.2 and U.S. Geological Survey method 1-2545-90 except that nitrate is reduced to nitrite by soluble nitrate reductase (NaR, EC 1.6.6.1) purified from corn leaves rather than a packed-bed cadmium reactor. A three-channel, air-segmented continuous-flow analyzer-configured for simultaneous determination of nitrite (0.020-1.000 mg-N/L) and nitrate + nitrite (0.05-5.00 mg-N/L) by the nitrate reductase and cadmium reduction methods-was used to characterize analytical performance of the enzymatic reduction method. At a sampling rate of 90 h(-1), sample interaction was less than 1% for all three methods. Method detection limits were 0.001 mg of NO2- -N/L for nitrite, 0.003 mg of NO3-+ NO2- -N/L for nitrate + nitrite by the cadmium-reduction method, and 0.006 mg of NO3- + NO2- -N/L for nitrate + nitrite bythe enzymatic-reduction method. Reduction of nitrate to nitrite by both methods was greater than 95% complete overthe entire calibration range. The difference between the means of nitrate + nitrite concentrations in 124 natural-water samples determined simultaneously bythe two methods was not significantly different from zero at the p = 0.05 level.

Effect of L-NAME on nitric oxide and gastrointestinal motility alterations in cirrhotic rats.

To investigate the effect of L-NAME on nitric oxide and gastrointestinal motility alterations in cirrhotic rats. Rats with cirrhosis induced by carbon tetrachloride were randomly divided into two groups, one n =13 receiving 0.5mg.kg(-1) per day of N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, for 10 days, whereas the other group (n =13) and control (n =10) rats were administrated the same volume of 9g.L(-1) saline. Half gastric emptying time and 2h residual rate were measured by SPECT, using (99m)Tc-DTPA-labeled barium sulfate as test meal. Gastrointestinal transition time was recorded simultaneously. Serum concentration of nitric oxide (NO) was determined by the kinetic cadmium reduction and colorimetric methods. Immunohistochemical SABC method was used to observe the expression and distribution of three types of nitric oxide synthase (NOS) isoforms in the rat gastrointestinal tract. Western blot was used to detect expression of gastrointestinal NOS isoforms. Half gastric emptying time and trans-gastrointestinal time were significantly prolonged(124.0 +/- 26.4 min; 33.7 +/- 8.9 min; 72.1 +/- 15.3 min; P<0.01), (12.4 +/- 0.5h; 9.5 +/- 0.3h; 8.2 +/- 0.8h; P<0.01), 2h residual rate was raised in cirrhotic rats than in controls and cirrhotic rats treated with L-NAME (54.9 +/- 7.6%,13.7 +/- 3.2%, 34.9 +/- 10.3%, P<0.01). Serum concentration of NO was significantly increased in cirrhotic rats than in the other groups (8.20 +/- 2.48) micromol.L(-1), (5.94 +/-1.07) micromol.L(-1) and control (5.66 +/- 1.60 micromol.L(-1), P<0.01. NOS staining intensities which were mainly located in the gastrointestinal tissues were markedly lower in cirrhotic rats than in the controls and cirrhotic rats after treated with L-NAME. Gastrointestinal motility was remarkably inhibited in cirrhotic rats, which could be alleviated by L-NAME. Nitric oxide may play an important role in the inhibition of gastrointestinal motility in cirrhotic rats.

Flow-injection analysis of nitrate by reduction to nitrite and gas-phase molecular absorption spectrometry.

Two flow-injection manifolds have been investigated for the determination of nitrate. These manifolds are based on the reduction of nitrate to nitrite and determination of nitrite by gas-phase molecular absorption spectrophotometry. Nitrate sample solution (300 microL) which is injected to the flow line, is reduced to nitrite by reaction with hydrazine or passage through the on-line copperized cadmium (Cd-Cu) reduction column. The nitrite produced reacts with a stream of hydrochloric acid and the evolved gases are purged into the stream of O2 carrier gas. The gaseous phase is separated from the liquid phase using a gas-liquid separator and then swept into a flow-through cell which has been positioned in the cell compartment of an UV-visible spectrophotometer. The absorbance of the gaseous phase is measured at 204.7 nm. A linear relationship was obtained between the intensity of absorption signals and concentration of nitrate when Cd-Cu reduction method was used, but a logarithmic relationship was obtained when the hydrazine reduction method was used. By use of the Cd-Cu reduction method, up to 330 microg of nitrate was determined. The limit of detection was 2.97 microg nitrate and the relative standard deviations for the determination of 12.0, 30.0 and 150 microg nitrate were 3.32, 3.87 and 3.6%, respectively. Maximum sampling rate was approximately 30 samples per hour. The Cd-Cu reduction method was applied to the determination of nitrate and the simultaneous determination of nitrate and nitrite in meat products, vegetables, urine, and a water sample.

An improved technique for the determination of oxidised nitrogen in natural waters with a Sequential Injection Analysis (SIA) system

An SIA system is proposed for the determination of oxidised nitrogen (nitrate + nitrite as N) in natural waters. A cadmium reductor, made of cadmium granules closely packed in a glass column reduces the nitrate to nitrite. The reduced nitrate and the nitrite present in the water samples is diazotised in the SIA system with sulphanilamide and coupled with N - (1-napthyl) ethylene diammoniumdichloride to form a highly coloured azo dye which is detected at 540 nm with a UV/Vis spectrophotometer. The proposed system is fully computerised and is able to monitor total oxidised nitrogen as nitrite at a frequency of 36 samples per hour with a standard deviation of < 1.2%. The calibration curve is linear up to 5 mg/l with a detection limit of 0.01 mg/l. WaterSA Vol.27(3) 2001: 355-360

The development of an on-chip micro-flow injection analysis of nitrate with a cadmium reductor

The development of a method to determine nitrate by micro-flow injection analysis (μFIA) is described, using electro-osmotic flow (EOF) control in a micro-chip with 300 μm wide and 115 μm deep channel wet etched in borosilicate glass. An in situ miniature copperised cadmium reductor column was produced by immobilisation within a micro-porous silica frit made from 10% formamide and 21% silicon dioxide. The reductor frit was located in the sample introduction reservoir of the device. Nitrate standards were placed in the sampling reservoir and an applied voltage of 50 V relative to a waste reservoir was used to move the nitrate ions through the reductor frit for μFIA. Silica frits without copperised cadmium were also introduced into the interconnecting channels of the μFIA device to promote EOF and minimise hydrodynamic movement of solutions. The nitrite produced on leaving the reductor frit was detected using the Griess diazo-coupling reaction. The reaction was monitored in situ using a micro-spectrometer. A calibration was obtained between 0.5 and 20 μM with a correlation coefficient of 0.985. The R.S.D. at 5 μM NO 3 − was 8.3% ( n=6) and the limit of detection (3 σ) was 0.51 μM (0.026 μg ml −1) NO 3 −.

Determination of traces of nitrite and nitrate in water by solid phase spectrophotometry

A simple and sensitive method for the determination of nitrite and nitrate in water using solid phase spectrophotometry is described. The method utilizes the quantitative and rapid sorption of the dye formed from nitrite, using the Griess reaction, into a thin layer of polyurethane foam (PUF) where a preconcentration factor of >140 has been achieved. Nitrate is pre-reduced using a cadmium reductor before applying the Griess reaction. The direct spectrophotometric measurement of the dye enriched in the solid foam phase has allowed the detection of as little as 5 and 40ngml−1 nitrite and nitrate, respectively. Optimization of the parameters affecting the quantitative formation and sorption of the dye into PUF has been considered. Analysis of natural water samples has been performed.

Monitoring of Hydrogen Peroxide, Nitrate and Nitrite in Rain Water

The relationship between hydrogen peroxide and nitrate and nitrite by monitoring these substances in rain water was investigated. For the determination of hydrogen peroxide, our previously reported FIA system was applied. For the determination of nitrate and nitrite, an FIA system consisting a copperized cadmium reduction column and 2,3-diaminonaphthalene (DAN) used as fluorescence substance was developed. Under the recommended conditions, it took 8 min to determine the sum of nitrate and nitrite while passing through the copperized cadmium reduction column; it took 6 min under the same condition to determine nitrite without passing through the column. The concentration of nitrate was calculated from the difference between the sum of nitrate and nitrite and nitrite. The detection limit, which was defined by a signal-to-noise ratio of 3, was calculated to be 0.1 µmol dm-3 for nitrite. Also, the relative standard deviation at 20 µmol dm-3 of nitrate was under 1.0% (n = 10). There was no interference from the major substances present in rain. The reaction scheme was based on the monitoring results.

Study of Cadmium Electrochemical Deposition in Sulfate Medium

The cadmium electrochemical deposition process from sulfate medium was studied by means of different electrochemical techniques in both stationary and nonstationary diffusion regimes. The kinetics of the electrochemical reduction of cadmium on solid cadmium electrodes was examined and the kinetic parameters are presented, as well as the diffusion coefficient derived from the different techniques. Temperature has an important effect on the cadmium reduction kinetics, and the activation energy of the process was evaluated. The electrochemical deposition of cadmium is a complex process due to the coexistence of adsorption and nucleation processes; the adsorbed electroactive species appears to be , and we propose a mechanism for cadmium electrodeposition on solid cadmium electrodes. © 2000 The Electrochemical Society. All rights reserved.

Comparative study of various methods of the heterogeneous reduction of nitrate ions

Working pH ranges of heterogeneous reductors of nitrate ions based on metallic cadmium, zinc, and brass as well as on cadmium-copper, cadmium-mercury, zinc-copper, and zinc-mercury galvanic couples were examined. Metallic cadmium and the cadmium-copper couple were selected as reductants; freshly prepared, these reductants provided the 100% reduction of nitrate ions to nitrite ions in the pH range from 3.4 to 9.5. A method was developed for prolonging the reducing properties of reductants based on metallic cadmium by permanently copper-plating these reductants. The relationship between the degree of reduction of nitrate ions in a cadmium reductor and the concentration of Cd2+ ions in the solution at the outlet of the reductor was determined.

Modification of the Cadmium Reduction Assay for Detection of Nitrite Production Using Fluorescence Indicator 2,3-Diaminonaphthalene

The measurement of nitric oxide (NO) is important for characterizing the regulatory roles of NO in various biological systems. In this communication we report that cadmium (Cd) reduction of nitrate (NO−3) to nitrite (NO−2) can be quantitated by using the fluorescence indicator, 2,3-diaminonaphthalene (DAN) to detect the sum of NO−3 and NO−2 (NO−x) from endothelial cells. This assay is at least 10-fold more sensitive than when Cd reduction is coupled with the spectrophotometric Greiss reaction and can be used to quantitate the small amounts of NO−x generated from the constitutive form of endothelial nitric oxide synthase (eNOS). In addition various P2 purinoceptor agonists and antagonists do not interfere the Cd reduction/DAN assay. Thus the Cd reduction/DAN assay can be used not only to characterize P2 purinoceptor release of NO−x from cultured endothelial cells but also to quantitate NO−x levels in serum.

Reverse Polarity Capillary Zone Electrophoretic Analysis of Nitrate and Nitrite in Natural Water Samples

This paper describes the application of reverse polarity capillary zone electrophoresis (CZE) for rapid and accurate determination of nitrate and nitrite in natural water samples. Using hexamethonium bromide (HMB) as an electroosmotic flow modifier in a borate buffer at pH 9.2, the resolution of nitrate and nitrite was accomplished in less than 3 min. CZE was compared with ion chromatographic (IC) and cadmium reduction flow injection analysis (Cd-FIA) methods which are the two most commonly used standard methods for the analysis of natural water samples for nitrate and nitrite. When compared with the IC method for the determination of nitrate and nitrite, CZE reduced analysis time, decreased detection limits by a factor of 10, cut laboratory wastes by more than 2 orders of magnitude, and eliminated interferences commonly associated with IC. When compared with the cadmium reduction method, CZE had the advantage of simultaneous determination of nitrate and nitrite, of being able to be used in the presence of various metallic ions that normally interfere in cadmium reduction, and of decreased detection limits by a factor of 10.