Organic nitrogen sampling

The Adamski [13] procedure is semiautomated. It gives an accuracy of 8.1% and a precision of 8.2% for seawater samples spiked with 3-35 p,g/l organic nitrogen. This procedure is based on the indophenol blue method and was employed using a Technicon AutoAnalyzer II system with the appropriate accessories. Various workers have described automated procedures for determination of low levels of organic nitrogen in seawater [15,16]. 

Equipment for automated Kjeldahl determinations of organic nitrogen in water and solid samples is supplied by Tecator Ltd. Their Kjeltec system 1 streamlines the Kjeldahl procedure resulting in higher speed and accuracy compared to classical Kjeldahl measurements. 

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. 

The vertical variation of the ratios of Org. N/Org. H in the same core sample shows that with a few exceptions the ratios increase regularly with increasing core depth. This means the organic hydrogen is more easily decomposed than organic nitrogen in recent sediments. 

Complete conversion of organic nitrogen to ammoniacal nitrogen is essential to obtain accurate and precise results. After the liquid has become clear and colorless, i t may be necessary to digest the sample for an additional -30 to 50... 

The thermogram of this sample is shown in Figure 8. The ammonium nitrate peak and the first peak of ammonium sulfate match closely the positions of standard compounds. However, the peak at 270°C is noticeably shifted from the second ammonium sulfate peak, although the overall appearance of the doublet is similar to that of ammonium sulfate. A tentative explanation of this observation is that the sample does not contain pure ammonium sulfate, but rather that some of the ammonium ions are replaced by a charged organic nitrogen complex. This complex should produce the right chemical shift (relative to ammonium) in the ESCA spectrum, decompose at a lower temperature than ammonium bisulfate, and hydrolyze to ammonium in water solution. 

Distillation of sample is often necessary for the removal of interfering contaminants. The sample is buffered at pH 9.5 with borate buffer prior to distillation. This decreases hydrolysis of cyanates (CNO ) and organic nitrogen compounds. 

Leinweber, P., Kruse, J., Walley, F. L., Gillespie, A., Blyth, R. I. R., and Regier, T. (2007). N K-edge XANES—An overview of reference compounds used to identify unknown organic nitrogen in environmental samples. J. Synchrotron Rad. 14,500-511. 

T. (2007). Nitrogen K-edge XANES—An overview of reference compounds used to identify unknown organic nitrogen in environmental samples. J. Synchrotron Rad. 14, 500-511. 

The candidate compound is added to the perfusate before the isolated liver is transferred to the perfusion setup. After 5 minutes recirculation in the system without the organ a sample of the perfusate is collected for determination of the starting concentration of the candidate compound (value at time 0). Then the isolated liver is connected to the perfusion chamber and subsequently samples of the perfusate are taken in 10 to 15 minute intervals as well as bile samples are taken in 15 minutes intervals for the determination of compound levels. The volume of excreted bile per 30 minutes is determined gravimetrically (difference between tube weight without and with bile per collection period) with the assumption that 1 g is equivalent to 1 ml of bile. If radioactive-labelled candidate compounds are used the intervals for bile collection can be much shorter (1 to 2 minutes). The liver is perfused for 2 hours and at the end of the perfusion experiment the liver is removed and immediately frozen for determination of tissue level of the compound in liquid nitrogen and later on stored at -20 °C until analysis. For analysis of tissue levels of the candidate compound the frozen livers are homogenized in water (1 g tissue in 1 ml water (or solvent to extract the candidate compound from the tissue)) using an ultra-turrax. 

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