Kjeldahl analysis micro

The boric acid method (a direct method) is simpler and is usually more accurate since it requires the standardization and accurate measurement of only one solution. However, the end point break is not so sharp, and the indirect method requiring back-titration is usually preferred for micro-Kjeldahl analysis. A macro-Kjeldahl analysis of blood requires about 5 mL blood, while a micro-Kjeldahl analysis requires about 0.1 mL. 

Albumin and globulins can be analyzed by the same procedure as for total proteins after fractionation by salting out with either sodium sulfate or sodium sulfite. More detailed information may be required about the protein fractions (a, j8, 7 globulins), in which case starch gel electrophoresis can be used to separate the proteins. Micro-Kjeldahl analysis of proteins is used when highly accurate data are required the biuret method is accurate to about 4%. 

The dextran-g-acrylamide sample PA-2 (Table 4) exhibited an intrinsic viscosity of 3.4 in water as compared to 0.3 for the unreacted dextran. Micro Kjeldahl analysis indicated 65% grafting (defined as weight of chain/total weight of graft copolymer x 100). 

The hydrolysis of 0.06 M BAA by papain is a first-order reaction under the conditions of assay (100). Specific activity (Gi) is expressed as K (first-order rate constant calculated in decimal logarithms) per milligram of protein nitrogen per milliliter of reaction mixture. Protein nitrogen can be estimated by the turbidometric method of Btlcher (36). The nitrogen content of standard papain solutions is determined by micro-Kjeldahl analysis. 

Example Figure 3.1, represents the absolute errors in nitrogen analysis by means of micro Kjeldahl s Method. Here, each vertical line labelled (xj - xt) designates the absolute deviation of the mean of the set from the true value. In Figure 3.1, A represents (xj - xf) the absolute error obtained by analyst-1 for the assay of benzyl-iso-thioureahydrochloride, whereas B represents (x2 - x() the absolute error obtained by analyst-2 for the assay of the same compound. 

Figure 3.1 Absolute Errors in N Analysis by a Micro Kjeldahl s Method.

L9. Levin, B., and Oberholzer, V. G., Paper electrophoresis of serum proteins with micro Kjeldahl nitrogen analysis of the protein fractions A comparison with free electrophoresis and salt fractionation methods. Am. J. Clin. Pathol. 23, 205 (1953). 

Nitrogen analysis was performed by a micro-Kjeldahl technique in a Technicon Autoanalyser. 

Soxhlet for fat and micro-Kjeldahl for protein). The preparation of freeze-dried meat mixtures to serve as calibration standards was also described in this work [32]. The availability of such pre-analysed, reconstitutable, shelf-stable calibration standards would facilitate the implementation of FTIR methods in the meat processing industry, in a similar manner as has been reported for milk analysis [33,34]. 

Spectral methods (spark source mass spectrometry SSMS, secondary ion mass spectrometry SIMS, inductively coupled argon plasma for emission spectroscopy ICAP-ES) which avoid separation steps are increasingly applied for multi-element analysis. Hot extraction is used for 0, N, H determinations. Oxygen is also determined by activation analysis, nitrogen after adaptation of classical methods (micro-Kjeldahl). Combination and comparison of different, independent methods are desirable, but hampered by the often limited availability of samples of actinides. 

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. 

Random copolymer synthesis Poly(acrylamide-co-sodium acrylates) (1) were prepared (reaction 5) by ammonium persulfate initiation in distilled water at a 10% monomers concentration at 25°C. The copolymers were isolated by precipitation into methanol, followed by freeze drying. The reactivity ratios were determined and the predicted copolymer composition was in excellent agreement with that experimentally determined by the micro Kjeldahl nitrogen analysis. Molar feed ratios of acrylamide to sodium acrylate varied from 96/4 to 55/45. 

As ammonium ions give a reduction wave in tetra-alkyl-ammonium hydroxide solutions, a method for the determination of nitrogen was devised. The method consists of mineralization by the conventional Kjeldahl method used in the semimicro or micro modification. Because waves at very negative potentials (e.g. of ammonium ions) are usually less reproducible than waves at more positive potentials, the accuracy of this method is somewhat lower than that for ordinary polarographic analysis. Other types of polarographic determinations of ammonium ions could be applied, e.g. using the anodic waves corresponding to the formation of salts with mercury or the condensation with phthalic dialdehyde (p. 142). 

The determination of ammonia after the regular or modified Kjeldahl digestion presents rather less serious problems than those already dis cussed. The advantages of the micro-Kjeldahl distillation (69, 80, 81, 82, 83) as compared with the macro>method, or even the semimicro-method are now generally recognized. A comparative study of the macro-and microscale determination in the analysis of flour, wheat and com for their protein content was made by Robinson and Shellenberger (27). The micro-Kjeldahl method has been used for systematic plasma protein analysis (84, 85), saliva proteins (86), milk proteins (87), and cerebrospinal fluid protein (88),... 

In these investigations it was also shown that the Kjeldahl process is suitable for the determination of nitrogen in titanium, both in its conventional form - dissolution in hydrofluoric acid, conventional distillation and photometric determination - if certain experimental conditions are observed, and in the modified form of pressure digestion, micro-Kjeldahl process, circulatory distillation and coulometric determination. These results can also be applied to the analysis of titanium alloys. 

FIGURE 5 Simple micro-Kjeldahl distillation apparatus. [Reprinted with permission from Cheronis, N. D., and Ma, T. S. (1964). Organic Functional Group Analysis. Wiley, New York Copyright 1964 Wiley.]... 

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