Nitrogen compounds, determination

The negative influence of nitrogen compounds on the HDS of thiophene was quantified at 7 MPa and 633 K. The adsorption constants of most nitrogen compounds, determined with the aid of a Langmuir-Hinshelwood model, follow the same trend as their proton affinities in the gas phase (Table II) (77). 

Surface concentration of nitrogen compounds, determined by integration of the Nls XPS signal group and catalyst activity (A) measured in the hydrogenation of cinnamic acid... 

Summary If the molecular weight is odd, then the compound contains an odd number of nitrogens. Fragment ions observed at even-mass numbers suggests the presence of nitrogen. The loss of ammonia is fairly common in nitrogen compounds and may not indicate exclusively that an amine is present. Chemical derivatization will easily determine if the unknown is a tertiary amine. 

There are numerous other compounds which can be determined in human body fluids. For some classes of compounds, e.g. nitrogen compounds, hormones, and sugars, a few reference materials are available. 

Nitrogen compounds commonly determined are creatinine, urea, and uric acid. Creatinine is an end product of the energy process occurring within the muscles, and is thus related to muscle mass. Creatinine in urine is commonly used as an indicator and correction factor of dilution in urine. Creatinine in serum is an indicator of the filtration capacity of the kidney. Urea is the end product of the nitrogen luea cycle, starting with carbon dioxide and ammonia, and is the bulk compoimd of urine. The production of uric acid is associated with the disease gout. In some cases, it appears that the excess of uric acid is a consequence of impaired renal excretion of this substance. 

Electron diffraction studies have also provided structural information for chalcogen-nitrogen compounds that are liquids or gases at room temperature, e.g., the 1,2,3,5-dithiadiazolyl radical [CF3CNSSN] (3)22 and the 1,3,2-di-thiazolyl [CF3CSNSCCF3] (4).23 The structure of the trithiatriazine (NSF)3 (5) has also been determined in the gas phase by a combination of electron diffraction and microwave spectroscopy, which shows that all three fluorine atoms are axial.24... 

Ultraviolet photo-oxidation techniques can be used as a method for organic nitrogen. The organic nitrogen compounds are oxidised to nitrate and nitrite then determined by the standard seawater analysis methods [17,18,23]. 

Table 3.28 The barriers of nitrogen inversion of BENA and related compounds determined with dynamic NMR...

The titrimetric determination of soil constituents is most commonly applied to a limited number of soil analyses, namely, organic carbon, nitrogen compounds, carbonates, and chlorides. Determination of acid content by titration is generally not done because the titration curves are not amenable to typical titration analysis. Because of the color of soil and the fact that it is a suspension when stirred, it is often necessary to remove the constituent of interest before titration. In other cases, it is possible to do a direct titration using an appropriate indicator. However, even in these cases, detection of the end point is difficult. 

Marty and Aim [177] described an automatic determination of the total oxygen demand of waste water. The method gives rapid results and correlates well with chemical oxygen demand and biochemical oxygen demand. Measurements of corrections are made for nitrogen compounds which are the principal interferents. 

A. Analysis of Wastewater and Natural Waters. The presence of certain anions in wastewater effluents can cause deterioration of natural water systems. Phosphorous and nitrogen can be present in several chemical forms in wastewaters. Phosphorous is usually present as phosphate, polyphosphate and organically-bound phosphorus. The nitrogen compounds of interest in wastewater characterization are ammonia, nitrite, nitrate and organic nitrogen. Analyses are often based on titrimetric, and colorimetric methods (3). These methods are time consuming and subject to a number of interferences. Ion Chromatography can be used to determine low ppm concentrations of these ions in less than thirty minutes with no sample preparation. 

Nearly 80% of the atmosphere consists of elemental nitrogen. This nitrogen, collected from different altitudes, exhibits a constant isotopic composition (Dole et al. 1954 Sweeney et al. 1978) and represents the zero-point of the naturally occurring isotope variations. Besides the overwhelming predominance of elemental nitrogen, there are various other nitrogen compounds in the atmosphere, which play a key role in atmospheric pollution and determining the acidity of precipitation. 

Analyzing and using spectroscopy to determine nitrogen compounds... 

A number of field studies have been carried out in which individual nitrogen compounds have been measured simultaneously with NO, to determine whether the individual species add up to the measured NO. In some cases there is indeed an approximate mass balance, whereas in others the sum of the individual species is less than the total measured NOr This discrepancy is often referred to as missing NO. Compounds that may contribute to the shortfall, when it exists, are discussed in Chapters 6.E.3 and 11.A.4. 

Figure 17.8—A non-conventional application of neutron activation. Neutron activation can be used to determine the composition of warheads. The drawing, reproduced by permission of EG G Ortec, demonstrates the principle of this approach. The graph represents part of a 7 spectrum obtained after only a few minutes from a warhead containing a nitrogen compound.

Vandoni [72] has reported that at 108.5°C guncotton nitrogen is evolved into the atmosphere mainly as nitrous oxide. He has determined the percentage proportion of nitrogen compounds in the decomposition products as follows ... 

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