Nitrous oxide spectroscopy

Quantitative aluminum deterrninations in aluminum and aluminum base alloys is rarely done. The aluminum content is generally inferred as the balance after determining alloying additions and tramp elements. When aluminum is present as an alloying component in alternative alloy systems it is commonly deterrnined by some form of spectroscopy (qv) spark source emission, x-ray fluorescence, plasma emission (both inductively coupled and d-c plasmas), or atomic absorption using a nitrous oxide acetylene flame. 

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. 

Atomic absorption spectroscopy is more suited to samples where the number of metals is small, because it is essentially a single-element technique. The conventional air—acetylene flame is used for most metals however, elements that form refractory compounds, eg, Al, Si, V, etc, require the hotter nitrous oxide—acetylene flame. The use of a graphite furnace provides detection limits much lower than either of the flames. A cold-vapor-generation technique combined with atomic absorption is considered the most suitable method for mercury analysis (34). 

One-step hydroxylation of aromatic nucleus with nitrous oxide (N2O) is among recently discovered organic reactions. A high eflSciency of FeZSM-5 zeolites in this reaction relates to a pronounced biomimetic-type activity of iron complexes stabilized in ZSM-5 matrix. N2O decomposition on these complexes produces particular atomic oj gen form (a-oxygen), whose chemistry is similar to that performed by the active oxygen of enzyme monooxygenases. Room temperature oxidation reactions of a-oxygen as well as the data on the kinetic isotope effect and Moessbauer spectroscopy show FeZSM-5 zeolite to be a successfiil biomimetic model. 

Flame Atomic Absorption Spectroscopy FAAS is one of the oldest analytical techniques and continues to be used in the analysis of food products. The analysis is usually performed in an air-acetylene or a nitrous oxide-acetylene flame. The technique measures the absorbance of electromagnetic radiation by the free atoms produced at high temperamre (1000-4000 K) [6]. 

A comparative study of the metal centers in cytochrome c oxidase from several bacterial sources, including Thermus thermophilus and P. denitrificans, using EPR and MCD spectroscopy has established that in both cases cytochrome a is liganded by two histidine oxidases and the Cua center is identical to that in bovine cytochrome c oxidase (105, 106). The properties of the cytochrome Os/Cub dimer have not been established to be identical, although ferrocytochrome 03 is high-spin ferrous, as expected. Recent studies of the MCD properties of the Cua center in cytochrome c oxidase and a copper center in nitrous oxide reductase (107,108) show that the two centers are virtually identical. The evidence from the EPR hyperfine structure of the copper center in nitrous oxide reductase suggests that the center in this enzyme is a mixed-valence Cu(I)/Cu(II) dimer, which raises the interesting prospect that the Cua center in cytochrome c oxidase is also a dimeric copper species. 

Atomic absorption spectroscopy is commonly used to determine Fe, Al, Mn, Cr and other metals. Standard solutions should be prepared with the same acid concentration as that of the test solutions. Apart from Al which requires a nitrous oxide/acetylene flame, these cations may be measured using an air/acetylene flame. These metals may also be measured by inductive coupled plasma analysis (ICP). 

Atomic absorption spectroscopy has been used to determine the amount of impurities in talc samples based on the chemical composition [35]. The detection of calcium, iron, and aluminum gave an indication of the mineral and chemical purity of the talc, whereas, analyses for chromium, manganese, nickel, and copper were of toxicological interest. The sample preparation involved an acid extraction with dilute hydrochloric acid to remove magnesium and calcium carbonates. Total dissolution of the sample was achieved with nitric/hydrofluoric acid mixture, followed by nitric/perchloric acid mixtures. Calcium was determined in the nitrous oxide/acetyiene flame and the other elements were detected in the air/acetylene flame. 

Heitland P. (2000) Verwendung von Spektrallinien in der ICP-OES im Wellenlangenbereich 125—190 nm, GIT Labor-Fachzeitschrijt 847—850. Christian G. D. and Feldmann F. J. (1971) A comparison study of detection limits using flame-emission spectroscopy with the nitrous oxide-acetylene flame and atomic-absorption spectroscopy, Appl Spectrosc 25 660-663. 

Charles AM, Suzuki I (1966b) Purification and properties of sulfitexytochrome c oxidoreductase from Thiobacillus novellus. Biochim Biophys Acta 128 522-534 Charnock JM, Dreusch A, Korner H, Neese F, Nelson J, Kannt A, Michel H, Gamer CD, Kroneck PM, Zumft WG (2000) Structural investigations of the Cua centre of nitrous oxide reductase from Pseudomonas stutter by site-directed mutagenesis and X-ray absorption spectroscopy. Eur J Biochem 267 1366-1381... 

Atomization of the sample is usually facilitated by the same flame aspiration technique that is used in flame emission spectrometry, and thus most flame atomic absorption spectrometers also have the capability to perform emission analysis. The previous discussion of flame chemistry with regard to emission spectroscopy applies to absorption spectroscopy as well. Flames present problems for the analysis of several elements due to the formation of refractory oxides within the flame, which lead to nonlinearity and low limits of detection. Such problems occur in the determination of calcium, aluminum, vanadium, molybdenum, and others. A high-temperature acetylene/nitrous oxide flame is useful in atomizing these elements. A few elements, such as phosphorous, boron, uranium, and zirconium, are quite refractory even at high temperatures and are best determined by nonflame techniques (Table 2). 

The separation of yttrium from the lanthanides is performed by selective oxidation, reduction, fractionated crystallization, or precipitation, ion-exchange and liquid-liquid extraction. Methods for determination include arc spectrography, flame photometry and atomic absorption spectrometry with the nitrous oxide acetylene flame. The latter method improved the detection limits of yttrium in the air, rocks and other components of the natural environment (Deuber and Heim 1991 Welz and Sperling 1999).Other analytical methods useful for sensitive monitoring of trace amounts of yttrium are X-ray emission spectroscopy, mass spectrometry and neutron activation analysis (NAA) the latter method utilizes the large thermal neutron cross-section of yttrium. For high-sensitivity analysis of yttrium, inductively coupled plasma atomic emission spectroscopy (ICP-AES) is especially recommended for solid samples, and inductively coupled plasma mass spectroscopy (ICP-MS) for liquid samples (Reiman and Caritat 1998). 

DeKlein cam, McTaggaet IP, Smith KA, Stevens RJ, Harrison R and Laughlin RJ (1999) Measurement of nitrous oxide emissions from grassland soil using photo-acoustic infrared spectroscopy, long-path infrared spectroscopy, gas chromatography, and continuous flow isotope-ratio mass spectrometry. Commun Soil Sci Plant Analysis 30 1463-1477. 

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