Nitrogen analysis nuclear methods

Detection limits down to the pg per kg level have been attained for the most favorable instrumental analyses (e.g., carbon and nitrogen in molybdenum and tungsten) and for radiochemical analyses (e.g., cadmium and thallium in zinc) at least if no nuclear interferences occur. This is below the concentration levels at which these impurities influence the material characteristics and below the detection limit attainable by more common methods of analysis. A precision (reproducibility) of a few percent is possible at the mg per kg concentration level in the most favorable cases. However, at higher concentration levels the precision will not improve significantly. Many systematic errors can be checked experimentally (e.g., interferences, yield of a radiochemical separation) others can be avoided experimentally (e.g., surface contamination). Systematic errors due to reagent blanks do not arise. 

Membranes and model membranes exhibit liquid crystalline behavior and this has been exploited in a number of studies to obtain valuable information on the structure and dynamics of membrane associated peptides and proteins as well as on the interaction of the peptides with the membranes themselves. NMR spectroscopy of nuclei such as proton, carbon, deuterium, nitrogen and phosphorus has been utilized for such purposes. Structure elucidation of membrane-associated peptides and proteins in oriented bilayers by solid-state NMR spectroscopy has been reviewed. A survey on the use of static uniaxially oriented samples for structural and topological analysis of membrane-associated polypeptides is available. The theoretical background has been dealt with and a number of examples of applications provided. In addition, ongoing developments combining this method with information from solution NMR spectroscopy and molecular modelling as well as exploratory studies using dynamic nuclear polarization solid-state NMR have been presented. The use of N chemical shift anisotropy, dipolar interactions and the deuterium quadrupolar split-... 

Activation analysis is a method that in some cases allows one to determine small amounts of nitrogen, of the order of 1 pg or less. It consists of irradiating the sample in a suitable generator of particles or rays, most frequently in a nuclear reactor, and measuring the decay of the new radioactive nuclides produced. The radioactivity A induced in such a manner can be calculated from equation (3), where N is the number of target atoms, a the cross section of the reaction, 0 the irradiation flux, t the irradiation time, and A the decay constant of the new nuclide . 

As follows from the data in Table 7, the introduction of NO2 and CH3 at positions 2 and 5 of the imidazole ring, respectively, leads to an increase in nuclear quadrupole coupling constants on both nitrogens of the ring and a decrease in the value of this parameter on the nitrogen from the NO2 group. Results of a bond population analysis carried out according to the Townes-Dailey method for imidazole and its derivatives are displayed in Table 8. 

As shown in a literature survey and critical evaluation of surface analysis methods by Quaglia and Weber (7), the most appropriate method to evaluate residual contamination of oxygen, nitrogen and carbon (for boron and phosphorus significant surface contaminations were never observed) on the surface of metallic samples is microanalysis by nuclear reactions (8-11). 

Although activation analysis with 14 MeV neutrons can also be used e.g. for the determination of nitrogen in metals (184), using the N(n,2n) N nuclear reaction, this method has been most useful for the determination of oxygen. 

---