Nitrogen titration

Assay (Note Use a combination pH-electrode for all titrations.) Accurately weigh between 0.100 and 0.150 g of sample, and dissolve it in 50 mL of ethanol. Perform the titration under a flow of nitrogen. Titrate with standardized 0.1 A tetrabutylammonium hydroxide in methanol or 2-propanol. Determine the volume of titrant needed to reach the first equivalence point (Vi mL) and the second equivalence point (V2 mL). 

Sher, I. H., Two step mixed indicator for Kjeldahl nitrogen titration. Anod. Chem. 27, 831-832 (1955). 

Figure 2. Intensity vs. distance plots for nitrogen titration at 3914 A. FHe = 16.1 X 10 < moles/sec. The intensity was normalized to 100 arbitrary units in all runs. Distance scale 1 unit = 0.531 cm. The number in each run refers to the pressure of nitrogen upstream of the flowmeter orifice and is approximately proportional to the flow rate of nitrogen...

As already observed, nitrogen titratable with formaldehyde represents only a minimum of the nitrogen contained in liberated peptides, due to the existence of di- and tri-nitrogenous bodies. 

Tops0e et determined active sites on iron catalysts for ammonia synthesis by nitrogen titration and point-time yields of ammonia (the ammonia molecules produced per second per active site in reactor) at 15% of conversion of equilibrium value at atmospheric pressure and 673 K and stoichiometric mixture. The difference between the values predicted by the models and obtained by experiments was less than three folds. 

Kjeldahl method An analytical method for the determination of nitrogen particularly in organic materials. The N is converted to NH with cone. H2SO4 and catalysts. After neutralization the NH j is distilled ofT and estimated by titration after absorption. 

The sample is pyrolyzed in an 80/20 mixture of oxygen and nitrogen at from 1050 to 1100°C the combustion gases are analyzed by iodine titration or by UV fluorescence. Up to 20% of the sulfur can escape analysis, however. 

Ammonia may be estimated by dissolving the gas in a known volume of standard acid and then back-titrating the excess acid. In a method widely used for the determination of basic nitrogen in organic substances (the Kjeldahl method), the nitrogenous material is converted into ammonium sulphate by heating with concentrated sulphuric acid. The ammonia is then driven off by the action of alkali and absorbed in standard acid. 

The imides, primaiy and secondary nitro compounds, oximes and sulphon amides of Solubility Group III are weakly acidic nitrogen compounds they cannot be titrated satisfactorily with a standard alkaU nor do they exhibit the reactions characteristic of phenols. The neutral nitrogen compounds of Solubility Group VII include tertiary nitro compounds amides (simple and substituted) derivatives of aldehydes and ketones (hydrazones, semlcarb-azones, ete.) nitriles nitroso, azo, hydrazo and other Intermediate reduction products of aromatic nitro compounds. All the above nitrogen compounds, and also the sulphonamides of Solubility Group VII, respond, with few exceptions, to the same classification reactions (reduction and hydrolysis) and hence will be considered together. 

Oxidizing the protein converts the nitrogen to NH4+. Why is the amount of nitrogen not determined by titrating the NH4+ with a strong base ... 

Analytical Procedures. Standard methods for analysis of food-grade adipic acid are described ia the Food Chemicals Codex (see Refs, ia Table 8). Classical methods are used for assay (titration), trace metals (As, heavy metals as Pb), and total ash. Water is determined by Kad-Fisher titration of a methanol solution of the acid. Determination of color ia methanol solution (APHA, Hazen equivalent, max. 10), as well as iron and other metals, are also described elsewhere (175). Other analyses frequendy are required for resia-grade acid. For example, hydrolyzable nitrogen (NH, amides, nitriles, etc) is determined by distillation of ammonia from an alkaline solution. Reducible nitrogen (nitrates and nitroorganics) may then be determined by adding DeVarda s alloy and continuing the distillation. Hydrocarbon oil contaminants may be determined by ir analysis of halocarbon extracts of alkaline solutions of the acid. 

Devarda s Method. Nitrogen in nitrates or nitric acid also may be deterrnined by the Kjeldahl method or by Devarda s method. The latter is both convenient and accurate when no organic nitrogen is present. The nitrate is reduced by Devarda s alloy to ammonia in an alkaline solution. The ammonia is distilled and titrated with standard acid. 

The mixture is kept for 3 hours at 105°C after the oxide addition is complete. By this time, the pressure should become constant. The mixture is then cooled to 50°C and discharged into a nitrogen-filled botde. The catalyst is removed by absorbent (magnesium siUcate) treatment followed by filtration or solvent extraction with hexane. In the laboratory, solvent extraction is convenient and effective, since polyethers with a molecular weight above about 700 are insoluble in water. Equal volumes of polyether, water, and hexane are combined and shaken in a separatory funnel. The top layer (polyether and hexane) is stripped free of hexane and residual water. The hydroxyl number, water, unsaturation value, and residual catalyst are determined by standard titration methods. 

Anhydrous ammonia is normally analy2ed for moisture, oil, and residue. The ammonia is first evaporated from the sample and the residue tested (86). In most instances, the amount of oil and sediment ia the samples are insignificant and the entire residue may be assumed to be water. For more accurate moisture determinations, the ammonia can be dissociated into nitrogen and hydrogen and the dewpoint of the dissociated gas obtained. This procedure works well where the concentration of water is in the ppm range. Where the amount of water is in the range of a few hundredths of a percent, acetic acid and methanol can be added to the residue and a Karl Fischer titration performed to an electrometricaHy detected end point (89—92). 

Ammonia and ammonium ions in industrial water streams, including waste-water streams, can be determined by either of two methods (ASTM Procedure D1426). In the first, the sample is buffered to a pH of 7.4 and distilled into a solution of boric acid where the ammonia nitrogen is deterrnined colorimetricaHy with Nessler reagents or titrated using standard sulfuric acid. 

Specifications, Analysis, and Toxicity. Dicyandiamide is identified quaHtatively by paper chromatography and quantitatively by ultraviolet spectrometry of the chromatogram. More commonly, total nitrogen analysis is used as a purity control or the dicyandiamide is converted by hydrolysis to guanylurea, which is determined gravimetrically as the nickel salt (50). Methods based on the precipitation of silver dicyandiamide picrate are sometimes used (51). Dicyandiamide can also be titrated with tetrabutylammonium hydroxide ia pyridine solution. Table 4 gives a typical analysis of a commercial sample. Dicyandiamide is essentially nontoxic. It may, however, cause dermatitis. 

Because the heavy ethyleneamines are very complex materials, assays by titration in aqueous and nonaqueous media are often performed (151). The result is usually expressed as an amine number or amine value, a measure of the total basic nitrogen content of the product. Titrimetric procedures are also available to define primary, secondary, and tertiary amine content (152). 

Chemical shifts of pyridine and the diazines have been measured as a function of pH in aqueous solution and generally protonation at nitrogen results in deshielding of the carbon resonances by up to 10 p.p.m. (73T1145). The pH dependence follows classic titration curves whose inflexions yield pK values in good agreement with those obtained by other methods. 

One 1-ml aliquot is added to 1.0 ml of freshly-distilled 1,2-dibromo-ethane (bp 132°C) in an oven-dried flask which contains a static atmosphere of nitrogen or argon. After the resulting solution has been allowed to stand at 25°C for 5 min, it Is diluted with 10 rat of water and titrated for base content (residual base) to a phenolphthalein endpoint with standard 0.100 M hydrochloric acid. The second 1-mL aliquot is added cautiously to 10 ml of water and then titrated for base content (total base) to a phenol phthalein endpoint with standard aqueous 0.100 M hydrochloric acid. The methyllithium concentration is the difference between the total base and residual base concentrations.2 Alternatively, the methynithiura concentration may be determined by titration with a standard solution of sec-butyl alcohol employing 2,2 -bipyridyl as an indicator. 

Into a suspension of 8 g of sodium acetate m 400 mL of a solution of 1 part acetic acid and 10 parts fluorotnchloromethane is passed at -75 C a stream of fluonne diluted to 10% with nitrogen The reacuon is stirred with a Vibromixer A solution of 4-methylacetanilide (20 mmol) in a mixture of dichloromethane and fluorotnchloromethane cooled to -75 °C i s added to 20 mmol of acetyl hypofluonte as determined by titration with potassium iodide After 5 min the mixture is poured into water, and the orgamc layer is washed with sodium bicarbonate soluaon and dried over anhydrous magnesium sulfate After concentrauon and column chromatography over silica gel and elution with chloroform, 2-fluoro-4-methylacetanilide IS obtained m 85% yield... 

A) Preparation of 3-Bromopropyltriphenylphosphonium Bromide Triphenylphosphine, 1.0 kg, and 770 grams of 1,3-dibromopropane are dissolved In 2.0 liters of xylene and the solution is stirred under a nitrogen atmosphere at 130°C. After 20 hours the mixture is cooled, and the crystalline product, which precipitates, is collected and washed with 20 liters of benzene. After drying in vacuo the product weighs 1,578 grams, MP 229°-230°C titration for bromide ion Found, T7.1% calculated, 17.2%. 

---