Molten sodium nitrite—potassium nitrite eutectic: the reaction of some compounds of molybdenum

Molybdenum(VI) oxide, ammonium molybdate and molybdic acid reacted in molten sodium nitrite—potassium nitrite eutectic to form orthomolybdate, nitrogen dioxide and nitric oxide (with nitrate as a secondary product), a more polymerised polymolybdate being formed as an intermediate product. Tungsten(VI) oxide reacted similarly but less rapidly. Molybdenum and tungsten metals reacted to form the orthoxyanion and nitrogen, the latter metal reacting considerably faster and forming smaller amounts of nitric oxide and nitrous oxide. Reaction temperatures and stoichiometries are given and reaction pathways suggested.     

Kinetics and mechanism of the cobalt phthalocyanine catalyzed reduction of nitrite and nitrate by dithionite in aqueous solution

The reaction of sodium nitrite with sodium dithionite was studied in the presence of cobalt(II) tetrasulfophthalocyanine, COII(TSPc)4-, in aqueous alkaline solution. The overall mechanism comprises the reduction of CoII(TSPc)4- by dithionite, followed by the formation of an intermediate complex between COI(TSPc)5- and nitrite, which undergoes two parallel subsequent reactions with and without nitrite as a reagent. Kinetic parameters for the different reaction steps of the catalytic process were determined. The final product of the reaction was found to be ammonia. Contrary to those found for the catalytic reduction of nitrite, the products of the catalytic reduction of nitrate were found to be dinitrogen and nitrous oxide. The possible catalytic reduction of nitrous oxide was confirmed by independent experiments. The striking differences in the reduction products of nitrite and nitrate are explained in terms of different structures of the intermediate complex between CoI(TSPc)5- and substrate, in which nitrite and nitrate are suggested to coordinate via nitrogen and oxygen, respectively.     

Theoretical studies on the formation of N-nitrosodimethylamine

The mechanisms of the formation of N-nitrosodimethylamine (NDMA) were studied at the MP2/6-311+G(d,p)//B3LYP/6-311+G(d,p) level of theory. We focused on the formation of NDMA from the reactions of dimethylamine (DMA) with nitrous acid and nitrite anion. Our calculations show that the reaction of DMA with nitrous acid is predicted to proceed via two distinct pathways: a concerted or a stepwise mechanism. Moreover, the energy barrier for the stepwise mechanism is somewhat higher than that for the concerted mechanism. The difference in these barriers indicates that the reaction of DMA with nitrous acid via the concerted mechanism is much more favored than that via the stepwise mechanism. In the other situation, our results demonstrate that the reaction of DMA with nitrite anion becomes feasible in the presence of carbon dioxide. Furthermore, this reaction proceeds via a stepwise pathway, in which CO₂ first attacks DMA, the result of which then reacts with nitrite anion. It is noteworthy that carbon dioxide appears to be an active catalyst to promote the formation of NDMA. Additionally, the effects of aqueous solvation on the reactions of DMA with nitrous acid and nitrite anion were investigated.     

N<Subscript>2</Subscript>O Production by Nitrifying Biomass Under Anoxic and Aerobic Conditions

The capacity of nitrifying biomass, grown in biofilms or in suspension, to reduce NO₂ ^- and NO₃ ⁻ under anoxic conditions was tested in batch experiments. The estimated reduction rates were 5 and 25 mg N per gram volatile suspended solids (VSS) per day for nitrate and nitrite, respectively, in the case of the nitrifying biofilms. Activity tests carried out with successive feedings indicated that no acclimation of the biomass to the tested conditions occurred, as the obtained reduction rates remained almost constant. Another series of activity assays was carried out with nitrifying suspended biomass, and the reduction rates for nitrate and nitrite were 30.4 and 48.9 mg N per gram VSS per day, respectively. N₂O and N₂ were the final gaseous products, and their percentages depended on the source of nitrogen feed. The specific production of nitrous oxide during nitrification was investigated during continuous experiments in a biofilm airlift suspension reactor. Specific production rates up to 46 mg N₂O–N per gram VSS per day were measured. The percentage of N₂O produced represented up to 34.4% of the ammonia oxidized. Nitrite accumulation, low dissolved oxygen concentrations, and the presence of organic matter favored the production of nitrous oxide. N₂O gas was not detected during the oxidation of nitrite even when organic matter was present. To prevent N₂O gas production in nitrifying systems, the operation at low dissolved oxygen concentrations, nitrite presence, or organic matter content should be avoided.     

Horseradish peroxidase catalyzed nitric oxide formation from hydroxyurea

Hydroxyurea represents an approved treatment for sickle cell anemia and a number of cancers. Chemiluminescence and electron paramagnetic resonance spectroscopic studies show horseradish peroxidase catalyzes the formation of nitric oxide from hydroxyurea in the presence of hydrogen peroxide. Gas chromatographic headspace analysis and infrared spectroscopy also reveal the production of nitrous oxide in this reaction, which provides evidence for nitroxyl, the one-electron reduced form of nitric oxide. These reactions also generate carbon dioxide, ammonia, nitrite, and nitrate. None of these products form within 1 h in the absence of hydrogen peroxide or horseradish peroxidase. Electron paramagnetic resonance spectroscopy and trapping studies show the intermediacy of a nitroxide radical and a C-nitroso species during this reaction. Absorption spectroscopy indicates that both compounds I and II of horseradish peroxidase act as one-electron oxidants of hydroxyurea. Nitroxyl, generated from Angeli's salt, reacts with ferric horseradish peroxidase to produce a ferrous horseradish peroxidase-nitric oxide complex. Electron paramagnetic resonance experiments with a nitric oxide specific trap reveal that horseradish peroxidase is capable of oxidizing nitroxyl to nitric oxide. A mechanistic model that includes the observed nitroxide radical and C-nitroso compound intermediates has been forwarded to explain the observed product distribution. These studies suggest that direct nitric oxide producing reactions of hydroxyurea and peroxidases may contribute to the overall pharmacological properties of this drug.     

Manganese dioxide graphite composite electrodes: application to the electroanalysis of hydrogen peroxide, ascorbic acid and nitrite.

The modification of carbon powder with manganese dioxide using a wet impregnation procedure with electrochemical characterisation of the modified powder is described. The process involves saturation of the carbon powder with manganese(II) nitrate followed by thermal treatment at ca. 773 K leading to formation of manganese(IV) oxide on the surface of the carbon powder. The construction of composite electrodes based on manganese dioxide modified carbon powder and epoxy resin is also described, including optimisation of the percentage of the modified carbon powder. Composite electrodes showed attractive performances for electroanalytical applications, proving to be suitable for the electrochemical detection of hydrogen peroxide, ascorbic acid and nitrite ions with limits of detection comparable to the detection limits achieved by other analytical techniques. The results obtained for detection of these analytes, together with composite electrodes flexible design and low cost offers potential application of composite electrodes in biosensors.     

Studies of the oxidation of iminodiacetic acid (IDA) and nitrilotriacetic acid (NTA) with lead dioxide suspension in nitric acid

The stoichiometry of the oxidation of IDA or NTA with lead dioxide suspension was studied by polarographic measurement and by derivative polarographic titration. One mole and two moles of Pb(IV) are reduced per mole of IDA and NTA respectively, with moderate speed at room temperature in nitric acid solutions. One mole each of carbon dioxide, formaldehyde and glycine are produced from the oxidation of 1 mole of IDA, and two moles of carbon dioxide, two moles of formaldehyde and one mole of glycine from 1 mole of NTA. The overall reaction in each case may be written as follows: Pb(IV) + IDA + H₂O → Pb(II) + CO₂ + HCHO + H₂NCH₂COOH + 2H⁺ 2Pb(IV) + NTA + 2H₂O → 2Pb(II) + 2CO₂ + 2HCHO + H₂NCH₂COOH + 4H⁺     

Identity confirmation of drugs and explosives in ion mobility spectrometry using a secondary drift gas

This work demonstrated the potential of using a secondary drift gas of differing polarizability from the primary drift gas for confirmation of a positive response for drugs or explosives by ion mobility spectrometry (IMS). The gas phase mobilities of response ions for selected drugs and explosives were measured in four drift gases. The drift gases chosen for this study were air, nitrogen, carbon dioxide and nitrous oxide providing a range of polarizability and molecular weights. Four other drift gases (helium, neon, argon and sulfur hexafluoride) were also investigated but design limitations of the commercial instrument prevented their use for this application. When ion mobility was plotted against drift gas polarizability, the resulting slopes were often unique for individual ions, indicating that selectivity factors between any two analytes varied with the choice of drift gas. In some cases, drugs like THC and heroin, which are unresolved in air or nitrogen, were well resolved in carbon dioxide or nitrous oxide.     

Anion effects on gas solubility in ionic liquids

This work presents the results of solubility measurements for a series of gases in 1-n-butyl-3-methyl imidazolium tetrafluoroborate and 1-n-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl) imide. The gases considered include benzene, carbon dioxide, nitrous oxide, ethylene, ethane, oxygen, and carbon monoxide. Carbon dioxide and oxygen solubilities are also reported in methyl-tributylammonium bis(trifluoromethylsulfonyl) imide, butyl-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide, and tri-isobutyl-methyl phosphonium p-toluenesulfonate. We report the associated Henry's constants and enthalpies and entropies of absorption. In general, benzene, followed by carbon dioxide and nitrous oxide, have the highest solubilities and strongest interactions with the ionic liquids, followed by ethylene and ethane. Oxygen had very low solubilities and weak interactions. Carbon monoxide had a solubility below the detection limit of our apparatus. Ionic liquids with the bis(trifluoromethylsulfonyl) imide anion had the largest affinity for CO(2), regardless of whether the cation was imidazolium, pyrrolidinium, or tetraalkylammonium. These results suggest that the nature of the anion has the most significant influence on the gas solubilities.     

Chemicals from forest products by supercritical fluid extraction

Supercritical acetone or methanol extraction of wood gave liquid products with a maximum yield of 74%. Approximately 5% of these complex products was identified as substituted guaiacols and levoglucosan. Acetone extract could substitute for 30% of the phenol in phenolic resins.

Resin and fatty acids were extracted from southern pine and waxes from Douglas-fir bark using supercritical carbon dioxide, nitrous oxide, propane or ethylene. Of these, propane and nitrous oxide gave the best yields.     

Automated simultaneous determination of nitrate and nitrite by pre-valve reduction of nitrate in a flow-injection system

Nitrate is reduced to nitrite by using the pre-valve in-valve reduction technique prior to the sampling system. One loop of a two-position sampling valve is replaced by a copperised cadmium column. Nitrite from the samples as well as nitrite formed in the reduction procedure is sampled by a second valve and introduced into the flow system. The two sampling valves are synchronised in such a way that two peaks are obtained, one corresponding to the nitrate plus nitrite and the other to the nitrite only. The method is suitable for the simultaneous determination of nitrate and nitrite at a sampling rate of up to 72 determinations per hour with coefficients of variation better than 1.96% for nitrate and 0.83% for nitrite.     

Study of the oxidation of ethylenediaminetetra-acetic acid with lead dioxide suspension in sulphuric acid

The stoichiometry of the reaction between lead dioxide suspension and EDTA was studied by derivative polarographic titration and determination of the products. Four moles of Pb(IV) are reduced per mole of EDTA with moderate speed at room temperature in sulphuric acid solutions. Four moles of carbon dioxide and 3 moles of formaldehyde are the products of the oxidation of 1 mole of EDTA. One mole of N-hydroxymethylethylenediamine is also thought to be produced. The overall reaction may be written as 4Pb(IV) + EDTA + 4H(2)O-->4Pb(II) + 4CO(2) + 3HCHO + H(2)NCH(2)CH(2)NHCH(2)OH + 8H(+). Ethylenediamine is also partly produced if a large excess of lead dioxide is used.     

A sensitive and accurate automatic coulometric detector system for enzymatically produced carbon dioxide

A system for the determination of carbon dioxide liberated in an enzyme reactor is described. The properties of the system are illustrated by the determination of urea. Enzymatically generated carbon dioxide is expelled by boiling, dried and determined coulometrically. The lowest concentration of urea which can be determined with a relative standard deviation of 5% is 1 μM. Compared with other methods based on immobilized enzymes for the determination of compounds as carbon dioxide, this sensitivity constitutes an improvement of about two orders of magnitude. Possible application to sea water is discussed.     

Manganese Dioxide Graphite Composite Electrodes Formed via a Low Temperature Method: Detection of Hydrogen Peroxide,Ascorbic Acid and Nitrite

Manganese dioxide modified carbon powder was prepared via a wet impregnation method from the solution of permanganate salt. After heating at 120 °C over night in air, the formation of manganese oxide was confirmed by cathodic stripping voltammetry. The synthesized material was used for fabrication of composite electrodes and their potential application in the field of electroanalysis investigated. The composite electrodes based on the manganese dioxide modified carbon powder proved to be useful as electrodes for detection of hydrogen peroxide, ascorbic acid and nitrite ions.     

Oxidation of Polyisoprene Popcorn Polymer. II. Gravimetric Analysis

Water, carbon dioxide, and condensable condensate produced during the oxidation of polyisoprene popcorn polymer were determined gravimetrically. For pure polyisoprene popcorn polymer from which 4.6% soluble polymer and volatiles were removed, the rates of water and carbon dioxide production during the early stages of the autoxidation were linear and amounted to approximately 2 moles of water and 0.2 moles of carbon dioxide for every 10 moles of oxygen reacted.

The generally accepted scheme for polyisoprene oxidation must be modified to account for the water production. Two possible routes for its synthesis are:

ROOH + ROOH → RO· + ROO· + H₂O

ROOH → RO· + ·OH

HO· + R → R· + H₂O     

Steam distillation methods for determination of ammonium,nitrate and nitrite

Steam distillation methods of determining ammonium, nitrate, and nitrite in the presence of alkali-labile organic nitrogen compounds are described. They involve the use of magnesium oxide for distillation of ammonium, ball-milled Devarda alloy for reduction of nitrate and nitrite to ammonium, and sulfamic acid for destruction of nitrite. The methods are rapid, accurate, and precise, and they permit nitrogen isotope-ratio analysis of ammonium, nitrate, and nitrite in tracer studies using ¹⁵N-enriched compounds. They give quantitative recovery of ammonium, nitrate and nitrite added to soil and plant extracts, and appear suitable for analysis of biological materials.     

Simultaneous determination of nitrate and nitrite by flow injection analysis

An automatic method for the simultaneous determination of nitrate and nitrite by flow injection analysis is described. Nitrate is reduced to nitrite with a copperized cadmium column. Nitrite is diazotized and coupled with N-(l-naphthyl)ethylenediammonium dichloride. The merging zones approach is used to minimize reagent consumption. The injector system is arranged so that two peaks are obtained, one corresponding to nitrite and the other to nitrite plus nitrate. A sampling rate of about 90 samples per hour is possible; the precision is better than 0.5% for nitrite in the range 0.1–0.5 mg l^t and 1.5% for nitrate in the range 1.0–5.0 mg l^t     

Copper Oxide – Graphite Composite Electrodes: Application to Nitrite Sensing

A simple method for the modification of carbon powder with copper oxides is presented. Carbon powder is impregnated with copper(II) nitrate by stirring carbon powder in copper(II) nitrate solution for 1 hour and subsequently thermally treated at 823 K. The modified carbon powder was characterized using electrochemical and spectroscopic techniques. The existence of both copper(I) and copper(II) oxides have been established. The copper oxide modified carbon powder was used for preparation of composite electrodes, and the electrochemical and electrocatalytic behavior of the resulting composite electrodes was studied. The copper oxide modified carbon powder – epoxy composite electrodes showed a high electrocatalytic activity for the nitrite detection in aqueous media, with the detection limit comparable or lower than detection limits obtained with other electrochemical sensors.     

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 mug ml(-1) nitrite and 0.06 to 1.6 mug ml(-1) nitrate with a detection limit of 0.01 mug ml(-1) for nitrite and 0.025 mug 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.     

Gas chromatographic separation of anaesthetic gases on a single column

Summary Gas chromatography has been employed in the separation of mixtures of air, carbon dioxide, nitrous oxide and a volatile anaesthetic (halothane, isoflurane or enflurane) on a single Chromosorb 101 column by temperature programming from room temperature. Calibration over the required range for the analysis of exhaled air, demonstrated good linearity with a repeatability for test mixtures of about 1%.