Measurement methods nitrous acid

Another important method of following protein hydrolysis is that due to Van Slyke, and consists in estimating the free amino groups liberated by treatment with nitrous acid, whereby gaseous nitrogen is evolved and measured in a special apparatus. 

If a solution of a nitrite is titrated in the ordinary way with potassium permanganate, poor results are obtained, because the nitrite solution has first to be acidified with dilute sulphuric acid. Nitrous acid is liberated, which being volatile and unstable, is partially lost. If, however, a measured volume of standard potassium permanganate solution, acidified with dilute sulphuric acid, is treated with the nitrite solution, added from a burette, until the permanganate is just decolorised, results accurate to 0.5-1 per cent may be obtained. This is due to the fact that nitrous acid does not react instantaneously with the permanganate. This method may be used to determine the purity of commercial potassium nitrite. 

Chlorocresol is a preservative commonly used in injections and its determination often involves the use of laborious extraction procedures in order to separate it from formulation components, followed by spectrophotometric measurement. A FIA method for chlorocresol was developed by utilising its reaction with nitrous acid to form a coloured nitro compound. The method was accurate to 99.5% of the true value of chlorocresol in a formulation and a precision of 1% was achieved. ... 

A kinetic study has been reported recently for the nitrosation of many symmetrical tertiary amines in aqueous acid-acetate buffers (Gowenlock et al., 1979). One experimental difficulty in tertiary amine nitrosations generally is that the reactions are much slower than for the analogous secondary amines, and are more conveniently studied at a higher temperature, typically 75°C, where the decomposition of nitrous acid is quite rapid. In this study, rate constants were obtained from the less accurate method of initial rate measurements. Nevertheless, for acidities less than pH 3.1, rate eqn (16) was established. The acid dependence is complicated by the protonation of the... 

Treatment of proteins with nitrous acid can lead to deamination of the lysyl residues as well as of the NH2-terminal residues. Kurosky and Hoffmann (1972) have identified three products of lysine deamination which elute from the 60 cm column of a Beckman 120C Analyzer at (1) the position of glutamic acid, (2) 7 min before glycine and (3) 10 min before tyrosine. Products (2) and (3), which are the major products formed, are believed to be s-hydroxynorleucine and its lactone respectively. The most accurate method for analyzing for lysine deamination is to measure the loss of lysine rather than to measure the three derivatives. 

A kinetic method for determination of aromatic amines was proposed, based on measuring the development of azo dyes (134) resulting from coupling a diazonium ion derived from a PAA analyte and the chromophoric substrate 1 -(4-hydroxy-6-methylpyrimidin-2-yl)-3-methylpyrazolin-5-one (133), as shown in equation 22. After a short induction period initial rate kinetics can be measured when the process is quite advanced, absorbance reaches a maximum and starts to recede due to oxidation of the azo dye by excess nitrous acid. Each PAA has to be calibrated for its molar absorption coefficient and reaction rate, for optimal measurement. A tenfold excess of 133 over the analytes ensures a pseudo... 

The appearance of the amino group can be measured by its reaction with nitrous acid, reaction with ninhydrin (colorimetrically or gasometrically), titration in acetone, and titration in the presence of formaldehyde. The appearance of a carboxyl group can be measured by titration in ethanol. Specific methods can be used for the determination of certain amino acids when these are liberated by hydrolysis. 

Two colorimetric methods are recommended for boron analysis. One is the curcumin method, where the sample is acidified and evaporated after addition of curcumin reagent. A red product called rosocyanine remains it is dissolved in 95 wt % ethanol and measured photometrically. Nitrate concentrations >20 mg/L interfere with this method. Another colorimetric method is based upon the reaction between boron and carminic acid in concentrated sulfuric acid to form a bluish-red or blue product. Boron concentrations can also be deterrnined by atomic absorption spectroscopy with a nitrous oxide—acetjiene flame or graphite furnace. Atomic emission with an argon plasma source can also be used for boron measurement. 

Adipic acid is of considerable importance since it is a precursor to nylon and polyester, which are extensively used in many products. Between two and three million tonnes are produced worldwide each year. Currently, its main method of manufacture is a costly, multistep process involving concentrated nitric acid. Nitrous oxide is produced as a by-product in such quantities that they measurably contribute to global warming and ozone depletion [24], A cleaner alternative to this process is clearly highly desirable. 

Rhenium can be analyzed by various instrumental techniques that include flame-AA, ICP-AES, ICP-MS, as well as x-ray and neutron activation methods. For flame-AA analysis the metal, its oxide, or other insoluble salts are dissolved in nitric acid or nitric-sulfuric acids, diluted, and aspirated directly into nitrous oxide-acetylene flame. Alternatively, rhenium is chelated with 8-hydroxy quinoline, extracted with methylisobutyl ketone and measured by flame-AA using nitrous oxide-acetylene flame. 

Biogenic silicon (BSI) was determined, with minor modifications, by the method of DeMaster (17). As adapted, the technique involved time-course leaching of <20-mg samples of particulate matter in 30 mL of 1.0% Na2C03 in a water bath at 85 °C. Silica in leachates was quantified either colorimetrically (Technicon autoanalyzer procedure) or by nitrous oxide flame atomic absorption. A high-temperature catalytic-combustion technique (Perkin Elmer 240C) was used for particulate organic carbon determinations. Particulate inorganic (carbonate) carbon was measured on the same instrument by CO 2 evolution after treatment of the particles with phosphoric acid. 

Recommended Methods. Two methods are suitable. In one, a large sample (usually 100 g) is dry ashed in a porcelain crucible. The resulting carbonaceous residue is ignited in a muffle furnace at 480°C. The ash is dissolved in dilute nitric acid, and potassium chloride and aluminum chloride are added to the solution. The molybdenum is measured by atomic absortion in a nitrous oxide-acetylene flame and related to a calibration curve. 

On the combination of nitrous air with respirable airs. Priestley s method of measuring the goodness of air by mixing with nitric oxide over water and observing the contraction was modified, and a formula given. Let ft be the ratio of nitrous air to vital air absorbed dans la formation d acide nitreux , a the quantity of pure air tested, b that of nitrous air mixed with it, c the residue. The quantities absorbed on mixing are ... 

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