Measurement methods nitrous oxide

From E. E. Pickett and S. R. Koirtyohann, Emission Flame Photometry—A New Look at an Old Method, Anal. Chem., 41, 28 A (1969). Used by permission of the American Chemical Society. In /rg/ml in aqueous solution, measured in nitrous oxide-acetylene or air-acetylene premixed flames formed by 5-10-cm slot burners. 

Tracer Type. A discrete quantity of a foreign substance is injected momentarily into the flow stream and the time interval for this substance to reach a detection point, or pass between detection points, is measured. From this time, the average velocity can be computed. Among the tracers that have historically been used are salt, anhydrous ammonia, nitrous oxide, dyes, and radioactive isotopes. The most common appHcation area for tracer methods is in gas pipelines where tracers are used to check existing metered sections and to spot-check unmetered sections. 

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. 

Sigman et al. [134] have described a bacterial method for measuring the isotopic composition of seawater nitrate at the natural-abundance level. The method is based on the analysis of nitrous oxide gas (N2O) produced quantitatively from nitrate by denitrifying bacteria. The classical denitrification pathway consists of the stepwise reduction of nitrate (NOp to nitrite (N02), nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2) ... 

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. 

The relative reactivities of various substances toward mercury triplets are expressed as quenching cross sections. These have been determined both by measuring the efficiency of quenching the 2537 A mercury phosphorescence494 and by Cvetanovic s chemical method employing nitrous oxide.495 In general, quenching cross sections are... 

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. 

NO can be measured by UV absorption. A highly sensitive and selective method is based on reaction of NO with O3 to produce an excited NO9 species that emits radiation in the 590- to 2600-nm range upon returning to the ground state. Nitrous oxide, N2O, is the most abundant oxide of nitrogen in the atmosphere and can be measured by IR absorption or gas chromatography with electron capture detection. 

Selective, sensitive techniques based on gas chromatography or atomic absorption have been developed. The trifluoroacetylacetonate derivative of beryllium may be extracted from aqueous solutions into benzene and the beryllium determined by gas chromatography (9). Under optimum conditions 4 X 10 13 g can be detected with an electron capture detector (JO). With a mass spectroscopic detector the detectible quantity is 2.5 X 10 n g, but the specificity of the method is greatly improved (II). Flame atomic absorption has been used to determine beryllium in many materials (12). The technique can be used to measure levels down to 0.02 fig Be/ml in aqueous solutions. However, some interferences may be encountered even with the nitrous oxide-acetylene... 

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. 

If separate reduction waves are observed for O2 and CO2 and there is no interference between the two it may be possible to measure the two gases using a double pulse method. This is analogous to the determination of oxygen and nitrous oxide on silver (vide infra). If the pulses are short enough this might be considered to be a simultaneous determination. 

Finally the flow cell described above has been used to monitor isoflurane in the presence and absence of oxygen (using the AQ scavenger method) [SI]- The response time to changes in gas concentration is less than ten seconds and it is suggested that this could be easily improved. Furthermore the mediated reductions of nitrous oxide and isoflurane are considered to be independent of each other. Thus it is also suggested that the sensor could be used to monitor both gases provided there was an independent measurement of one of them available. This however, remains to be seen. 

After T720 was tentatively characterized as an aquated electron with nitrous oxide and electron transfer studies, the quantum yield for the production of the aquated electron In dilute natural waters containing dissolved organic matter and In humic substance extract was measured by the comparlslon method. In this method the literature value for the extinction coefficient of the solvated electron at 720 nm was used (21). The excited state absorption of T720 was measured. These were used In algebraic ratio to an actlnomlter for which a quantum yield had already been thoroughly determined. 

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