DETERMINATION OF NITROGEN FRACTIONS

Biitikofer, U., Ruegg, M., and Ardo, Y. (1993). Determination of nitrogen fractions in cheese, evaluation of a collaborative study. Lebensm. Wiss. Technol. 26, 271-275. 

Mariotti, A., Germon, J.C., Hubert, P., Kaiser, R, Letolle, R., Tardieux, A. and Tardieux, P. 1981 Experimental determination of nitrogen kinetic isotope fractionation some principles illustration for the denitrification and nitrification processes. Plant and Soil 62 413-430. 

Collect the eluate in fractions of about 4 ml and combine the fractions corresponding to each peak. For each combined fraction carry out the determination of nitrogen as per BP (1993). Not more than 10% of the total nitrogen is present in the combined fraction associated with non-retained proteins. 

A4. Anderson, A. B., The direct determination of nitrogen in protein fractions separated by electrophoresis in filter paper. Biochem. J. 52, Proc. x (1952). 

Drushell, H. V. (1977). Determination of nitrogen in petroleum fractions by combustion with chemiluminescent detection of nitric oxide. Anal. Chem. 49, 932-936. 

Molinie R, Kwiecien RA, Silvestre V, Robins RJ (2009) Determination of nitrogen-15 isotope fractionation in tropine evaluation of extraction protocols for isotope ratio measurement by isotope ratio mass spectrometry. Rapid Commun Mass Spectrom 23 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.) 4031 1037. doi 10.1002/ rcm.4344... 

For determination of dissolved fractions, the samples are acidified (pH 1-2) and purged for 2 h with 100 mL/min of filtered high-quality nitrogen to remove the interfering preservation reagent (hydrogen azide) fi-om solution. 

Finally, Table 2 shows enthalpy calculations for the system nitrogen-water at 100 atm. in the range 313.5-584.7°K. [See also Figure (4-13).] The mole fraction of nitrogen in the liquid phase is small throughout, but that in the vapor phase varies from essentially unity at the low-temperature end to zero at the high-temperature end. In the liquid phase, the enthalpy is determined primarily by the temperature, but in the vapor phase it is determined by both temperature and composition. 

The rapid increase in the separation factors observed for the individual series of columns reflected not only the improvement in the intrinsic selectivities of the individual selectors but also the effect of increased loading with the most potent selector. Although the overall loading determined from nitrogen content remained virtually constant at about 0.7 mmol g for all CSPs, the fractional loading of each selector increased as the number of selectors in the mixture decreased. Thus, the whole method of building block selection and sublibrary synthesis can be also viewed as an amplification process. 

The researeh on dehydroepiandrosterone (DHEA) is limited beeause of the laek of radiolabeled metabolites. Robinzon et al. [126] showed that, using pig liver mierosomes, the radiolabeled metabolites of DHEA can be prepared in stable, pure form for bioehemical smdies. They utilized pig liver microsomal (PLM) fractions to prepare pH]-labeled 7a-hydroxy-DHEA (7a-OH-DHEA), 7[3-hydroxy-DHEA (7P-OH-DHEA), and 7-oxo-DHEA substrates from 50 pM [1,2,6,7-3H]DHEA. The metabolites were separated by silica gel PLC plates using ethyl aeetate-hexane-gla-eial aeetic acid (18 8 , v/v) as the mobile phase, extracted with ethyl aeetate, and dried under a stream of nitrogen. The purity of markers was determined with the use of TLC and GC/MS. 

Pass the solution derived from Section 6.2.2 through a Cig cartridge (conditioned prior to use successively with 5mL of acetonitrile and 10 mL of water), then elute interfering substances with 15 mL of acetonitrile-water (3 17, v/v) and discard the eluate. Elute imibenconazole-debenzyl with 20 mL of acetonitrile-water (2 3, v/v) and collect the eluate in a 100-mL separatory funnel (imibenconazole-debenzyl fraction). Elute imibenconazole with 20 mL of acetonitrile-water (17 3, v/v) and collect the eluate in a 100-mL separatory funnel (imibenconazole fraction). Add 30 mL of 20% sodium chloride aqueous solution and 40 mL of ethyl acetate to each separatory funnel and shake the funnel with a mechanical shaker for 5 min. Collect the ethyl acetate extract, dry the extract with anhydrous sodium sulfate and transfer into a 100-mL round-bottom flask. Concentrate the ethyl acetate extract to near dryness by rotary evaporation and dry with a stream of nitrogen. Dissolve the residue of each fraction in acetone for gas chromatographic determination as in Section 6.3. 

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