Methods nitrogen

Zeolite Type Zeolite Lattice Zeolite Content % Int./Na Y Internal Std. Nitrogen Method Kaolinite... 

International Standard Organization. 1984. Water quality. Determination of Kjeldahl nitrogen. Method after mineralization with selenium. ISO 5663. International Organization for Standardization, Case Postale 56, CH-1211, Geneva 20 Switzerland. 

Urea Nitrogen Macro and Micro. The flow diagram of the urea nitrogen method is shown in Fig. 18. The method originally used for citrulline (FI) has been adapted to the determination of urea (Ol). Although the method has had limited success in routine clinical chem-... 

A 1-10 mg specimen (typically between 2 and 5 mg) is heated at a constant rate between 0.2 and 2 K/s in the lower chamber. Decomposition can take place in nitrogen (method A) or in a mixture of nitrogen and oxygen (method B). When method A is used, charforming specimens do not decompose completely and leave a solid residue. In this case, the volatiles are mixed with a metered supply... 

It is emphasized that the phase transition on the iron catalysts takes place at so low a relative pressure that it does not invalidate the BET-nitrogen method. 

Many investigations have been made of the sorption of water vapour by various forms of montmorillonite and vermiculite. In a study of the effect of increasing the outgassing temperature of natural vermiculite on the sorption of water vapour, Gregg and Packer (1954) obtained a set of unusual stepwise Type I isotherms, all of which displayed low-pressure hysteresis. It is of interest that the location of the step riser, at about p/p° = 0.02, appeared to be almost independent of the outgassing temperature. The water sorption capacities were reported to be far greater than would be expected for adsorption on the external areas, as determined by the BET-nitrogen method (i.e. 1-2 m2 g" ). 

Although the BET theory is based on an unrealistic model, there is a generally accepted convention [8] of applying the BET-nitrogen method in order to obtain the values of the apparent surface area. The results are shown in Table 2, which also includes the range of linearity of the BET equation. It can be observed in this table that the apparent surface areas increase significantly with the degree of bum-off. 

Fig. 6. Pore size distribution curves for silica SiC12T calcined at 500 C obtained by using various methods (1) - nitrogen method (2) - TG method (water).

Nitrogen method TG method (benzene) TG method (water) ... 

The Kjeldahl nitrogen method is based on the fact that, upon digestion with sulfuric acid and catalysts, the organic material is destroyed and most forms of nitrogen are converted to ammonia. When the digestion mixture is made alkaline, the ammonia is released. The ammonia is removed by distillation, absorbed, and titrated. These reactions can be represented as follows ... 

While it cannot be denied that the soundest methods for the estimation of pure albumin in aqueous solution are likely to be those based on elementary composition (i.e., carbon or nitrogen) or measurement of peptide bonds (e.g., far-ultraviolet spectrophotometry) the oft-repeated statement that the Kjeldahl nitrogen method for determining plasma proteins is theoretically more sound than others is untrue. This method suffers no less than others from the disadvantage that the individual plasma proteins possess different nitrogen contents (Table 3). 

The first two experiments yielded the following results the NH concentration began to increase from the first to the second day, it reached its maximum at the seventh, then nitrification followed. The PO " concentration increased from the second to the fifth day. The concentration of the dissolved OM in the first experiment determined by permanganate oxidisabil-ity, the albuminoid nitrogen method and BOD exceeded the concentrations observed in the control experiment without plankton by the sixtieth day (Fig. 2). 

Many physicochemical assays are established to quantify the protein mass. It is determined by exploiting the extinction coefficient in optical density measurements or by colorimetric assays such as the Bradford, Lowry, bicinchoninic (BCA), and biuret assay [13, 14]. Albeit easy to perform, these colorimetric assays suffer from inaccuracies that are due to the use of inappropriate standards like bovine serum albumin. If relevant standards are not available, quantitative amino acid analysis [6], the (micro-)Kjeldahl nitrogen method [14, 15] or gravimetry as very accurate but time-consuming alternatives can be applied. 

Total amino resin content can be determined in the solid residue by the Kjeldahl nitrogen method or by CHN analysis. In melamine resins titration of melamine with perchloric acid is possible. The total level of free and combined formaldehyde can be determined by phosphoric acid decomposition and by distillation. 

The comprehensive method determines the nitrogen content for all forms of nitrogen compounds (nitrite, nitrate, urea, organic nitrogen, and ammonia), which upon distillation can be collected in a known amount of sulfuric acid and titrated with sodium hydroxide. A great deal of time is consumed in performing this classical nitrogen method. Note Boric acid may be used for collection of ammonia in the distillation step rather than sulfuric acid. 

FIGURE 2.90 Relationship between changes in free energy and concentration of unfrozen water (a) and IPSD (bound cluster) size distributions (b) in frozen aqueous suspensions of silicalites calculated with the NMR cryoporometry (bound water) and MND (nitrogen) methods. 

None the less the so-called BET low temperature nitrogen method is still widely applied as the standard procedure for determining the surface area of fine powders and porous materials. It was stated by Sing [118], that there are two principal causes for its popularity. First, under favourable conditions, the BET plot can provide a reliable estimation of the monolayer capacity - especially by means of the nitrogen adsorption at 77K - and secondly, the BET approach is easy both to apply and to comprehend. 

Cohn (161) reported that he and Hughes had succeeded in guanidinating bovine and horse serum albumin with 0-methyl iso urea. These derivatives were immunologically similar to the imtreated protein. Hughes (377) has found that an alkalinity of pH 10.0 was necessary for this reaction. It was practically complete in a few days at 0°C., as determined hy the Van Slyke amino nitrogen method. Greenstein (162), for an entirely differ t purpose, exposed solutions of e albumin to fairly hi ... 

U V fluorescent sulfur detection and chemiluminescent nitrogen methods have been developed for total sulfur only, nitrogen only or simultaneous sul-fur/nitrogen analysis. These systems provide quick automated analysis to estimate the type and amount of sulfur and nitrogen-containing additives present in a polyolefin sample, i.e. slip agents, antistatics. 

A method applicable in the presence of organic matter, such as in asthma powders, depends on the reduction of the nitrate to ammonia by nascent hydrogen but in some cases this may give rise to substantial blanks. The reduction method is included below under Determination of Nitrogen Method D (a) but an alternative method which has also been used for preparations of this type is as follows ... 

G.W Rice, J.J. Richard, A.P D Silva, and VA. Fassel. Gas chromatographic-atmospheric pressure active nitrogen method for organomercuty speciation in environmental samples. J. Assoc. Off. Anal. Chem., 65(1), 14 (1982). 

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