Nitrite sensitive

Gao et al. reported on nitrite sensitive liquid membrane electrodes based on metalloporphyrin derivatives Ir(TPP)Cl, Ir(TMPP)Cl and chloro(2-nitro-5,10, 15,20-tetraphenylporphyrinato)indium. The electrodes were found to have a high selectivity for nitrite in the presence of a number of interfering ions with the following selectivity pattern ... 

Li J, Wu X, Yuan R, Lin H, Yu R. Cobalt phthalocyanine derivatives as neutral carriers for nitrite-sensitive poly(vinyl chloride) membrane electrodes. The Analyst 1994 119 1363-6. 

A nitrite-sensitive material has been developed by Fabre et al. with a poly(iV-methylpyrrole) film incorporating a metal-substituted heteropolyanion [(H20)Fe XWn039]" (X = P, n = 4, or X = Si, n = 5) as a doping anion [38C1-382]. Such a film was electrochemically stable and exhibited an efficient elec-trocatalytic activity vis-a-vis the nitrite reduction. In contrast, poor results were obtained when PPy was used as the immobilization matrix [383, 384]. The key step of this electrocatalytic process was the formation of an iron-nitrosyl complex generated from the replacement of H2O initially coordinated to the iron center by an NO group, the reduction of which led to the catalytic conversion of NO2 into ammonium ions [385, 386]. The measured catalytic currents were linear with the nitrite concentration over the range 1 X 10 to 3 X 10 M [382]. Furthermore, anions such as NOJ,... 

Li J-Z, Pang X-Y, Yu R-Q (1994) Substituted cobalt phthalocyanine complexes as carriers for nitrite-sensitive electrodes. Anal Chim Acta 297 437-442... 

A method suitable for analysis of sulfur dioxide in ambient air and sensitive to 0.003—5 ppm involves aspirating a measured air sample through a solution of potassium or sodium tetrachloromercurate, with the resultant formation of a dichlorosulfitomercurate. Ethylenediaminetetraacetic acid (EDTA) disodium salt is added to this solution to complex heavy metals which can interfere by oxidation of the sulfur dioxide. The sample is also treated with 0.6 wt % sulfamic acid to destroy any nitrite anions. Then the sample is treated with formaldehyde and specially purified acid-bleached rosaniline containing phosphoric acid to control pH. This reacts with the dichlorosulfitomercurate to form an intensely colored rosaniline—methanesulfonic acid. The pH of the solution is adjusted to 1.6 0.1 with phosphoric acid, and the absorbance is read spectrophotometricaHy at 548 nm (273). 

Authors are designed row sensitive and selective test-systems for analysis of heavy metals, active chlorine, phenols, nitrates, nitrites, phosphate etc. for analysis of objects of an environment and for control of ions Ee contents in the technological solutions of KH PO, as well as for testing some of pharmacological psychotropic daigs alkaloids (including opiates), cannabis as well as pharmaceutical preparations of phenothiazines, barbiturates and 1,4-benzodiazepines series too. 

Note Note that the diazotization of primary aromatic amines can also be achieved by placing the chromatogram for 3 — 5 min in a twin-trough chamber containing nitrous fumes (fume cupboard ). The fumes are produced in the empty trough of the chamber by addition of 25% hydrochloric acid to a 20% sodium nitrite solution [2, 4], iV-(l-Naphthyl)ethylenediamine can be replaced in the reagent by a- or -naphthol [10, 14], but this reduces the sensitivity of detection [2]. Spray solutions Ila and lib can also be used as dipping solutions. 

Sodium thiosulphate is a reducing agent. In the presence of sodium nitrate it leads to explosive mixtures, which are sensitive if they are heated. Under the same conditions the detonation is immediate with sodium nitrite. 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

An unstable compound of low impact-sensitivity [1]. In a comparative study of a series of cobalt complexes ranging from triamminecobalt(III) nitrite to ammonium hexanitrocobaltate(3—), the title compound burned the fastest [2],... 

Mixtures of sodium (or its alloy with potassium) and nitromethane, trichloroni-tromethane, nitrobenzene, dinitrobenzene, dinitronaphthalene, ethyl nitrite, ethyl nitrate or glyceryl nitrate are shock-sensitive, the sensitivity increasing with the number of nitro groups. 

To date, electrochemical (amperometric) detection of NO is the only available technique sensitive enough to detect relevant concentrations of NO in real time and in vivo and suffers minimally from potential interfering species such as nitrite, nitrate, dopamine, ascorbate, and L-arginine. Also, because electrodes can be made on the micro- and nano-scale these techniques also have the benefit of being able to measure NO concentrations in living systems without any significant effects from electrode insertion. 

FIGURE 1.13 Absorbance measurement of 2, 7 -dichlorodihydrofluorescein (DCDHF), a peroxynitrite-sensitive dye, as a function of nitrite (1 mM) and NADH (1 mM) introduction to a solution containing 100 pM DCDHF and 30mU/mL NR under ambient (a) and nitrogen saturated conditions (b). As can be seen, die absorbance of DCDHF increases upon nitrite and NADH introduction only under an oxygen atmosphere, indicative of peroxynitrite production. (Reprinted with permission from Elsevier Publishing [117].)... 

Instead of sodium nitrite, isoamyl nitrite is sometimes used as a nitrosating agent in synthesis of the benzotriazole ring. With this reagent, the reaction conditions are very mild allowing survival of acid sensitive groups. In an example of such a reaction, methyl 3,4-diamino-2-methoxybenzoate 1286 is treated with isoamyl nitrite at room temperature. The reaction is fast and provides methyl 4-methoxybenzotriazole-5-carboxylate 1287 in 62% yield, isolated by simple filtration off the precipitate (Equation 31) <2006JME4762>. 

Van den Berg [131] used this technique to determine nanomolar levels of nitrate in seawater. Samples of seawater from the Menai Straits were filtered and nitrite present reacted with sulfanilamide and naphthyl-amine at pH 2.5. The pH was then adjusted to 8.4 with borate buffer, the solution de-aerated, and then subjected to absorptive cathodic stripping voltammetry. The concentration of dye was linearly related to the height of the reduction peak in the range 0.3-200 nM nitrate. The optimal concentrations of sulfanilamide and naphthyl-amine were 2 mM and 0.1 mM, respectively, at pH 2.5. The standard deviation of a determination of 4 nM nitrite was 2%. The detection was 0.3 nM for an adsorption time of 60 sec. The sensitivity of the method in seawater was the same as in fresh water. 

Gianguzza and Orecchio [147] have carried out comparative trials of various methods for estimating nitrites in seawaters. These workers compared a method using sulfanilic acid/a-naphthylamine complexes with a method using sulfanilamide/N( 1-naphthyl) ethylenediamine complexes for the determination of nitrites in saline waters. The second method has the greater sensitivity and lower detection limits. The former method is subject to interference from chlorides, and this interference can be completely eliminated by the coupling diazotisation procedure of the latter method. 

In this development of a flow injection method for the determination of nitrate andnitrite, Anderson [168] chose the Shinn [155] method to reduce nitrate and nitrite because of its high sensitivity and relative freedom from interferences. Anderson [168] used flow injection in the photometric determination of nitrite and nitrate with sulfanilamide and N-( 1-naphthyl) ethylenediamine as reagents, as discussed next. The detection limit is 0.05 xm for nitrite and 0.1 xm for nitrate at a total sample volume of 200 iL. Up to 30 samples can be analysed per hour with relative precision of about 1%. 

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