Nitrogen In Organic Compounds Research Articles

Mass-Spectrometric Method of Measurement of Isotopic Content of Nitrogen in Organic Compounds

Mass-Spectrometric Method of Measurement of Isotopic Content of Nitrogen in Organic Compounds

Organic nitrogen in PM<sub>2.5</sub> aerosol at a forest site in the Southeast US

Abstract. There is growing evidence that organo-nitrogen compounds may constitute a significant fraction of the aerosol nitrogen (N) budget. However, very little is known about the abundance and origin of this aerosol fraction. In this study, the concentration of organic nitrogen (ON) and major inorganic ions in PM2.5 aerosol were measured at the Duke Forest Research Facility near Chapel Hill, NC, during January and June of 2007. A novel on-line instrument was used, which is based on the Steam Jet Aerosol Collector (SJAC) coupled to an on-line total carbon/total nitrogen analyzer and two on-line ion chromatographs. The concentration of ON was determined by tracking the difference in concentrations of total nitrogen and of inorganic nitrogen (determined as the sum of N-ammonium and N-nitrate). The time resolution of the instrument was 30 min with a detection limit for major aerosol components of ~0.1 μg m−3. Nitrogen in organic compounds contributed ~33% on average to the total nitrogen concentration in PM2.5, illustrating the importance of this aerosol component. Absolute concentrations of ON, however, were relatively low (<1.0 μg m−3) with an average of 0.16 μg m−3. The absolute and relative contribution of ON to the total aerosol nitrogen budget was practically the same in January and June. In January, the concentration of ON tended to be higher during the night and early morning, while in June it tended to be higher during the late afternoon and evening. Back-trajectories and correlation with wind direction indicate that higher concentrations of ON occur in air masses originating over the continental US, while marine air masses are characterized by lower ON concentrations. The data presented in this study suggests that ON has a variety of sources, which are very difficult to quantify without information on chemical composition of this important aerosol fraction.

THE MOST WELL-KNOWN REARRANGEMENTS IN ORGANIC CHEMISTRY AT HAND

Rearrangement occurs in many organic reactions. Rearranged products result from the thermodynamic stability facet. The widely used rearrangements are those which take place on the carbonium ions. Wagner-Meerwein rearrangement is undoubtedly the best example of this kind. Rearrangements on heteroatoms such as oxygen and nitrogen in organic compounds are best illustrated by those of Hofmann and Beckmann. Cope and Claisen rearrangements are among the most well-known pericyclic reactions governed by the Woodward-Hoffmann rules. These reactions are decribed in detail here, while the rest are compiled in tables. Few industrial applications of crucial rearrangements are importantly outlined. [Chem. Educ. Res. Pract. Eur.: 2002, 3, 33-64]

Microdetermination of nitrogen in organic compounds by the sodium fusion-spectrophotometric method

In the absence of the preferred Dumas nitrogen apparatus or the more sophisticated nitrogen analyzers, a micro-Parr bomb can serve to determine microquantities of nitrogen in organic compounds. The sample or compound, either solid or nonaqueous liquid, is decomposed by fusing with metallic sodium in a sealed nickel bomb. The nitrogen is converted to sodium cyanide. The excess sodium is decomposed with absolute ethanol. The solution is adjusted to pH 7.1-7.2 with dilute hydrochloric acid and analyzed for cyanide by the Chloramine-T and mixed pyridine/pyrazolone reagent method. The absorbance of the blue color formed is measured with a spectrophotometer at 615 nm. The amount of cyanide found is converted to the equivalent nitrogen in the compound. The method is not as rapid as desired but it is handy, simple, and economical. As with any micro or semimicro method, this procedure is sensitive to technique. Compounds must contain carbon and be essentially free of moisture. 5 references, 1 table.

Automatic potentiometric micro-determination of basic nitrogen in organic compounds.

Basic nitrogen is determined at the milligram level by potentiometric titration in a non-aqueous medium. Acetic acid is a suitable solvent for substances with very different structures, except from some amino acids that are soluble in perchloric acid and may therefore be determined by back-titration. The behaviour of some organic nitrogen compounds that do not exhibit a basic character because of a resonance phenomena, contrary to what is expected, is also explained. Titration graphs with sharp inflection points allow exact determinations for all the compounds examined.

Presentation of Niche Measure Relationships when More than Three Resource Classes are Involved

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The qualitative test for nitrogen in organic compounds using the oxygen flask method

The oxygen flask method has been found superior to the traditional sodium fusion method, but for compounds containing both nitrogen and bromine a negative test for nitrogen is produced.

Biological oxidation of nitrogen in organic compounds and disposition of N-oxidized products.

N-Oxidation of nitrogenous compounds has been shown to be of special biological interest: many N-oxidized aromatic amines have been recognized to be ultimate mutagens and carcinogens; ferrihemoglobin formation is mediated by a series of N-oxidized products, and allergic disorders arise from interaction of such compounds with cellular macromolecules. There are several types of nitrogen containing compounds which undergo N-oxidation in biological systems. These include aliphatic and aromatic primary, secondary, and tertiary amines, heterocyclic secondary amines, heteroaromatic and alicyclic tertiary amines, primary and secondary amides as well as imines, hydrazines, and azo compounds. N-Oxidation products tend to be formed in small amounts and are often labile. Colorimetric methods of analysis, although frequently used, tend to be nonspecific and other products may interfere with the measurement. Chromatographic methods allow direct identification and quantification and take into account the lability of these metabolites. Direct quantification of N-oxidation products by GLC has been achieved by derivatisation to give more stable compounds. Recently HPLC has been successfully employed to resolve some of the analytical problems. The natural occurrence of a large variety of N-oxidized compounds in plant and animal tissues has been recognized. Similarly, a broad spectrum of nitrogenous drugs and other xenobiotics are converted to the corresponding N-oxidation products after in vivo administration to men and animals. These include analgesics, narcotics, psychotherapeutic drugs, sympathomimetics, chemotherapeutic agents, and carcinogens. The extent of N-oxidation of the individual amine compounds has been found to vary with the species investigated. Organ specificity and genetic control are further factors to be considered. The site of N-oxidation of amine compounds has been detected to be located in the endoplasmic reticulum of the cell. By using isolated hepatic microsomal fractions, in vitro experiments demonstrated the N-oxidation process to exhibit typical mixed-function oxidation characteristics. Nevertheless, there is still considerable controversy as to the enzymology of N-oxidation. Experiments with classic inhibitors and modifiers of the cytochrome P-450 mixed-function oxidase system suggest the N-hydroxylation of primary alkyl- and arylamines to be a hemoprotein-dependent reaction. N-Oxidation of secondary and tertiary alkyl- and arylamines is believed to proceed by a cytochrome P-450-independent pathway represented by a FAD-containing flavoprotein oxidase. However, evidence has accumulated demonstrating some involvement of cytochrome P-450 in the N-oxidation of N,N-dialkylanilines, pyridines, and some alicyclic tertiary amines. The hemoprotein system also appears to mediate N-oxidation of acetamides, imines, and monoalkylhydrazines. Steric features of the individual amine compounds have been found to influence the N-oxygenating capacity of the enzyme systems. Basicity and nucleophilicity of the amine substrates has been taken to predict whether the preferred route of N-oxidation is via the cytochrome P-450 system or the flavoprotein amine oxidase. The value of such concept is discussed. Other mechanisms such as the peroxidatic transformation of aniline to phenylhydroxylamine by catalase and chloroperoxidase are discussed. N-Oxidation products undergo further metabolism by various enzyme systems. The most important reactions are: (1) Reduction of hydroxylamines, nitro compounds, and N-oxides; (2) oxidation of hydroxylamines and oxims; (3) oxim-amide rearrangement; (4) N-oxide dealkylation; and (5) N-hydroxyacetamide glucuronidation, sulfation, acylation, and deacetylation. The latter transformation reactions effect special reactivity of the metabolites with tissue macromolecules.

Ultramicrodetermination of nitrogen in organic compounds: XI. Removal of interference from iodine for the sealed-tube method

The interference from iodine in ultramicrodetermination of nitrogen in organic compounds with the sealed-tube method was investigated and attempts to minimize it are discussed. Use of 30 to 50 mg G.R. tungsten trioxide prepared by heating in a current of air at 800 °C for 1 hr is recommended. Errors were almost always within ±0.3%.

On the behaviour of nitrogen in organic compounds after combustion with various methods

On the behaviour of nitrogen in organic compounds after combustion with various methods

Ultramicrodetermination of nitrogen in organic compounds: IX. A new method for handling volatile liquids in the sealed-tube method

A new method for handling volatile liquids in the ultramicrodetermination of nitrogen by the sealed-tube method, using a weighing tube of thin-walled capillary containing a capillary of sample, is described. Before sealing the weighing tube, the air present can be replaced with a gas mixture of CO 2 and CH 4 having approximately the density of air. The weighing tube is broken by tapping prior to combustion, and analysis is not affected by volatilization.

Ultramicrodetermination of nitrogen in organic compounds: X. Handling of volatile solid samples in the sealed-tube method

A method for handling volatile solid samples in the ultramicrodetermination of nitrogen by the sealed-tube method is described. It involves the use of a thin-walled capillary in which the sample is sealed after replacing an air in that with gas mixture. Satisfactory results were obtained with volatile solid samples.

Ultramicrodetermination of nitrogen in organic compounds: 8. Weighing of hygroscopic and volatile samples for the sealed-tube method

A new method for handling hygroscopic and volatile samples for decimilligram determination of organic nitrogen by the sealed-tube method was described. It involves the use of a copper-foil capsule in which hygroscopic and volatile samples can be dried to constant weight and weighed. Satisfactory results were obtained with this method.

Ultramicrodetermination of nitrogen in organic compounds: VI. Capillary immutability due to glass corrosion by various solutions

The capillary immutability due to corrosion of glasses exposed to various solutions was studied. The analytical error of volume change caused by glass corrosion in a micro- and ultramicronitrometer was discussed. The present work has shown that the graduated tube of a decimicronitrometer made of borosilicate glass, which is used frequently in Dumas method, should be recalibrated after 1.5–2.3 months use. We therefore recommend the sealed tube method using an improved nitrometer for ultramicrodetermination of nitrogen in organic compounds.

Ultramicrodetermination of nitrogen in organic compounds: VII. Determination of total nitrogen in dilute aqueous solution by sealed-tube method

With a modified combustion tube having a ball of 2-ml capacity with a fine tip, our sealed-tube method was used to determine the nitrogen contents of nonvolatile organic compounds of dilute aqueous solution with nitrogen levels from 1 to 70 ppm. A drop of diluted sulfuric acid was added to the sample, which was freeze-dried, then burnt.

A rapid method for the microdetermination of nitrogen in organic compounds using a flushed-oxygen combustion tube

A micromethod to determine nitrogen in organic compounds of 1–1.5 mg has been studied by the combustion method where oxygen is flushed into an empty combustion tube heated at 850 °C. The flushing nozzle is consisted of two silica filters in a L-tube and oxygen flowing out of the nozzle rapidly oxidizes the organic vapor gasified in a sample heater. Excess oxygen and nitrogen oxides are absorbed and reduced with reduced copper heated at 500–600 °C.

Ultramicrodetermination of nitrogen in organic compounds: Centimilligram determination of nitrogen with sealed tube method

A new improved nitrometer was developed for centimilligram determination of nitrogen by the sealed-tube method. A combustion tube having an internal volume of 1 ml was used and the sample was weighted in a boat made of copper foil, which was made by a simple device. The accurate volume of a gas granule of the blank was evaluated by observation with a micrometer microscope. A standard deviation of 0.240% was rapidly and conveniently obtained with organic compounds having a range of 5.94–66.4% nitrogen.

Ultramicrodetermination of nitrogen in organic compounds: IV. Thermal behavior of a gas in a nitrometer due to local variations of temperature

To more accurately measure nitrogen temperature for ultramicrodetermination of nitrogen, the variation of local temperature in the nitrometer was investigated. Two or three parts of the nitrometer were simultaneously measured. Based on our results, we designed a new improved nitrometer equipped with a water jacket.

Apparatus for elemental micro analysis of organic substances by frontal gas chromatography

An automatic microanalyser for the determination of carbon, hydrogen, and nitrogen in organic compounds is described. One analysis takes about 10 min and the sample weight is 0.5–2.5 mg. Statistical analysis of the results shows the apparatus works with satisfactory precision (sC=0.2, sN=0.2, and sH=0.1% absolute). The conventional Pregl-Dumas combustion system is used under dynamic conditions with either addition of oxygen or merely an inert atmosphere. The combustion products are diluted with helium, allowed to reach diffusion equilibrium under fixed conditions, and then chromatographed by the frontal technique and detected with a katharometer.

Ion-exchange method for simultaneous microgram detection of sulfur, chlorine, iodine, and nitrogen in organic compounds

Ion-exchange method for simultaneous microgram detection of sulfur, chlorine, iodine, and nitrogen in organic compounds