Effect of ammonia on the response of the electron capture detector (ECD)

The effect of ammonia on the electron capture detector (ECD) response has been investigated. Nitrogen with different ammonia concentrations (5–20%) was used as make-up gas. Compared to pure nitrogen, the ECD response decreased when the ammonia concentration in the make-up gas was 5%. However, the response increased when the ammonia concentration was 20%. The response factor of 4-chlorophenol increased 4 fold when ammonia was 20%. Also, di- and tri-chlorophenols increased by 30–50%. The nitroaromatic compounds responses increased by about 2–3.7 times with 20% ammonia in the make-up gas. The signal-to-noise (S/N) increased when 20% ammonia in nitrogen was used as make-up gas compared to pure nitrogen. Also, the detector linearity increased by 50% with ammonia.     

Modification of active carbon and zeolite as ammonia separation materials for a new de-NO<Subscript>x</Subscript> process with ammonia on-site synthesis

Ammonia adsorption and desorption behavior of surface treated active carbon (AC) and ion-exchanged Y zeolite, as ammonia separation and storage materials for a new de-NO_x process with ammonia on-site synthesis, were studied. Surface oxidized AC adsorbed more ammonia than non-treated AC due to ammonium ion formation. These materials were found to increase weak adsorption of ammonia and to be useful for pressure swing adsorption. Transition metal ion exchanged Y-zeolite adsorbed more ammonia (both weak and strong form) than Na Y-zeolite due to ammine complex formation. These materials adsorb and desorb more ammonia than treated AC when used for temperature swing adsorption.     

Plasmophore sensitized imaging of ammonia release from biological tissues using optodes

A plasmophore sensitized optode was developed for imaging ammonia (NH(3)) concentrations in muscle tissues. The developed ammonia sensor and an equivalent non plasmophore version of the sensor were tested side by side to compare their limit of detection, dynamic range, reversibility and overall imaging quality. Bio-degradation patterns of ammonia release from lean porcine skeletal muscle were studied over a period of 11 days. We demonstrate that ammonia concentrations ranging from 10nM can be quantified reversibly with an optical resolution of 127 μm in a sample area of 25 mm × 35 mm. The plasmophore ammonia optode showed improved reversibility, less false pixels and a 2 nM ammonia detection limit compared to 200 nM for the non-plasmophore sensor. Main principles of the sensing mechanism include ammonia transfer over a gas permeable film, ammonia protonation, nonactin facilitated merocyanine-ammonium coextraction and plasmophore enhancement. The vast signal improvement is suggested to rely on solvatochroism, nanoparticle scattering and plasmonic interactions that are utilized constructively in a fluorescence ratio. In addition to fundamental medicinal and biological research applications in tissue physiology, reversible ammonia quantification will be possible for a majority of demanding imaging and non imaging applications such as monitoring of low ammonia background concentrations in air and non-invasive medicinal diagnosis through medical breath or saliva analysis. The nanoparticle doped sensor constitutes a highly competitive technique for ammonia sensing in complex matrixes and the general sensing scheme offers new possibilities for the development of artificial optical noses and tongues.     

Gas-sensitive electrode applied to the continuous measurement of atmospheric ammonia

A method for the determination of ammonia in air is described. Air is pumped directly onto the head of a gas-sensitive electrode, the cap of which contains KCl and a low concentration of NH₄Cl. For calibration, cleaned air flows over the surface of an ammonia solution. The ammonia concentration of this solution is measured continuously with a second electrode. The mean ammonia concentration in the gas phase is calculated from the ammonia loss in the solution. The detection limit for gaseous ammonia is 5 μg m^?3. Effective measures to avoid interferences are described.     

Excited state hydrogen transfer in fluorophenol.ammonia clusters studied by two-color REMPI spectroscopy

Two-color (1 + 1') REMPI mass spectra of o-, m- and p-fluorophenol.ammonia (1 ration) clusters were measured with a long delay time between excitation and ionization lasers. The appearance of NH(4)(NH(3))(n-1)(+) with 100 ns delay after exciting the S(1) state is a strong indication of generation of long-lived species via S(1). In analogy with the phenol.ammonia clusters, we conclude that an excited state hydrogen transfer reaction occurs in o-, m- and p-fluorophenol.ammonia clusters. The S(1)-S(0) transition of o-, m- and p-fluorophenol.ammonia (1 : 1) clusters were measured by the (1 + 1') REMPI spectra, while larger (1 ration) cluster (n = 2-4) were observed by monitoring the long-lived NH(4)(NH(3))(n-1) clusters action spectra. The vibronic structures of m- and p-fluorophenol.ammonia clusters are assigned based on vibrational calculations in S(0). The o-fluorophenol.ammonia (1 : 1) cluster shows an anharmonic progression that is analyzed by a one-dimensional internal rotational motion of the ammonia molecule. The interaction between the ammonia molecule and the fluorine atom, and its change upon electronic excitation are suggested. The broad action spectra observed for the o-fluorophenol.ammonia (1 : n) cluster (n>== 2) suggest the excited state hydrogen transfer is faster than in m- and p-fluorophenol.ammonia clusters. The different reaction rates between o-, m- and p-fluorophenol.ammonia clusters are found from comparison between the REMPI and action spectra.     

Ion exchange of some transition metal cations on hydrated titanium dioxide in aqueous ammonia solutions

The adsorption of transition metal cations on hydrated titanium dioxide in complexing ammonia and amine solutions has been studied as a function of ammonia (amine) concentration. The relationships between the distribution coefficients and ammonia concentration as well as the effects of various amines on sorption of transition metals indicate that a coordinate bond is formed between the metal ions and the hydroxy groups of the sorbent. The distribution coefficients of silver(I) and cobalt(III), which form strong ammonia complexes in aqueous solutions, decrease with increasing concentration of ammonia already at concentrations exceeding 10^–3. mol·dm^–3. Cations of zinc, manganese and mercury which form much weakerammonia complexes do not exhibit any effect of ammonia concentration in the whole range investigated. In the case of sorption of macroamounts of ammonia or amine complexes of silver, the molecular sieve effect plays an important role. The differences in the affinity of hydrated titanium dioxide for ammonia solvates of various transition metal ions can serve as a tool for effective separation of these ions in ammonia solutions.     

Ru上有氧条件下氨分解的动力学研究

IthasbeenshownthatRuisvalidforthesyn thesisanddecompositionofammonia[1,2 ] .FurtherstudyofammoniaadsorptionanditsdecompositionproductsdesorptiononRuwillbeimportant .Previ ousstudiesofammoniaadsorptiononRumainlyfo cusedontheammoniasynthesisandhydrogenpro ductionintheabsenceofoxygen[3] ,onlyafewinves tigationsonammoniadecompositioninthepresenceofoxygenhavebeenreported[4 ,5] ,andtheeffectofad sorbedoxygenontheratesofammoniadecompositionandproductformationonRuarestillnotwellunder stood .Inthispa…     

Sorption of gaseous ammonia on sulfonated macroreticular ion exchangers

The amount of gaseous ammonia sorbed on dry sulfonated macroreticular ion exchangers with different contents of divinylbenzene was found to be greater than the number of sulfonic acid groups. The excess ammonia could be removed by washing with water. With ion exchangers containing more than 20% of divinylbenzene a certain amount of chemically bonded ammonia could not be removed, even by elution with strong acid. Sorption of ammonia occurred also on dry ion exchangers fully neutralized with sodium ion, and in that case also, ammonia could only partially be removed by water from higher crosslinked samples. On desorption into a gaseous phase the amount of desorbed ammonia was proportional to the surface area of the ion exchanger, since desorption occurred only from surface layers. The results obtained indicate that ammonia migrates among acid groups located within the mass of the ion exchanger.     

利用紫外光离子源高场不对称波形离子迁移谱快速、现场检测水中氨的含量

氨是水体主要的污染物之一,其含量是水质评估的重要参数。本研究采用真空紫外光离子源-高场不对称波形离子迁移谱(Ultraviolet photoionization high field asymmetric waveform ion mobility spectrometry, UVFAIMS)技术,发展一种的水中氨含量的现场快速检测方法。通过对比标准氨样品和水中微量氨UV-FAIMS 谱图峰的特征补偿电压(Compensation voltage, CV)值,确定了水中HN+4的特征离子峰位置;研究了不同分离电压(Dispersion voltages, DV)下HN+4谱图峰位置的关系,获得了HN+4的特征识别系数α2和α4分别为2.21×10-5 Td-2和-1.45323×10-9 Td-4;通过不同浓度样品的信号响应,研究了UV-FAIMS 对水中氨的检出限,在信噪比为3的情况下达到了9.2 μg/ L。本研究为水中氨现场检测提供了一种快速、无需前处理的技术手段。     

Enhanced ammonia oxidation on BDD induced by inhibition of oxygen evolution reaction

Electrochemical oxidation of ammonia (NH₃ and NH₄ ⁺ ) on boron-doped diamond (BDD) electrode was studied using differential electrochemical mass-spectrometry (DEMS) and chronoamperometry. Electro-oxidation of ammonia induces inhibition of the oxygen evolution reaction (OER) due to adsorption of the ammonia oxidation products on the BDD surface. The inhibition of the OER enhances ammonia electro-oxidation, which becomes the main reaction. The amino radicals, formed during ammonia oxidation, trigger a reaction chain in which molecular oxygen dissolved in solution is involved in the ammonia electro-oxidation. Nitrogen, nitrous oxide, and nitrogen dioxide were detected as the ammonia oxidation products, with nitrogen being the main gaseous product of the oxidation.     

Ammonia decomposition catalysis using non-stoichiometric lithium imide

We demonstrate that non-stoichiometric lithium imide is a highly active catalyst for the production of high-purity hydrogen from ammonia, with superior ammonia decomposition activity to a number of other catalyst materials. Neutron powder diffraction measurements reveal that the catalyst deviates from pure imide stoichiometry under ammonia flow, with active catalytic behaviour observed across a range of stoichiometry values near the imide. These measurements also show that hydrogen from the ammonia is exchanged with, and incorporated into, the bulk catalyst material, in a significant departure from existing ammonia decomposition catalysts. The efficacy of the lithium imide–amide system not only represents a more promising catalyst system, but also broadens the range of candidates for amide-based ammonia decomposition to include those that form imides.     

Ammonia and carbon dioxide permeability through perfluorosulfonic membranes

Transmembrane transport of ammonia and carbon dioxide through perfluorosulfonic membranes in ionic forms of transition metals was studied in a wide temperature interval. The different patterns of the temperature plots of the permeability coefficient of ammonia were found for different ionic forms of the membrane. An increase in the ammonia permeability with an increase in the moisture contents of the membrane also depends on its ionic form. The effects observed are explained by the different structures of water—ammonia complexes formed with metal ions. The mechanism of transmembrane transport of ammonia through perfluorosulfonic membranes in various ionic forms is discussed.     

A Continuously Regenerable Chiral Ammonia Borane for Asymmetric Transfer Hydrogenations

A novel chiral ammonia borane was designed and developed through the dehydrogenation of ammonia borane with a chiral phosphoric acid, which was highly effective for the asymmetric transfer hydrogenation of imines and β‐enamino esters to afford high levels of reactivities and enantioselectivities. Significantly, this chiral ammonia borane can be continuously regenerated during the transfer hydrogenation with the assistance of water and ammonia borane, which made it possible to obtain satisfactory results using only 0.1 mol % of the chiral phosphoric acid. Notably, the role of chiral phosphoric acid is to produce the chiral ammonia borane.     

Surface species in the direct amination of methanol over Brønsted acidic mordenite catalysts

Quantitative in situ infrared spectroscopy in combination with kinetic analysis is utilized to derive mechanistic aspects for the reaction of methanol with ammonia on Brønsted acidic mordenite. Under non-reactive conditions, a coadsorption complex between methanol and ammonia is found, in which only ammonia is in direct interaction with the Brønsted acid sites of the zeolite. This complex is proposed to be the precursor for the formation of protonated methylamines in the zeolite pores which are formed in sequential order up to tetramethylammonium ions. These methylamines are unable to desorb under reaction conditions in the absence of ammonia. They leave the surface either by ammonia adsorption assisted desorption or by scavenging of methyl groups from protonated methylamines by ammonia. Both steps are concluded to be potentially rate determining.     

Zur Bestimmung von Ammoniak in Lebensmitteln

Controlling the steam distillation which was used for ammonia determination applying normal pressure, we could state that food containing protein did release ammonia even in the presence of very little alkali (pH 7,4). By using steam distillation with magnesium oxide, for mild alkalisation, the amounts of ammonia were lower than with buffer solutions of the same alkalinity; comparatively, with buffer solutions of lower alkalinity magnesium oxide causes a higher amount of ammonia. These effects are mainly caused by the influence of the (boiling-)temperature of 100° C; besides of this the amounts of ammonia obtained are depending not only on the type of substance and alkalinity of the solution, but also on the intensity of heating and the duration of the distillation. Variations in the relationship between the amount of sample and the solution for alkalisation effect a change of alkalinity and by this always different yields of ammonia. Therefore, this method cannot be acknowledged for determinations of ammonia in substances containing easily decomposable protein compounds, even not under fixed conditions.     

The determination of free ammonia in ambient air with diffusion/denuder tubes

Ammonia is important in atmospheric chemistry because it neutralises acidic species and increases the pH of cloud droplets. Data on the concentration of free ammonia in the atmosphere are sparse because it is difficult to separate free ammonia from particulate ammonium salt aerosol. A manual method for the determination of free ammonia in air is described based on diffusion/denuder tube separation of ammonia from ammonium salt aerosol. When air is drawn through a tube coated with a selective absorbent (here oxalic acid) separation is achieved because the gaseous species diffuses much more rapidly to the tube wall than the particles. After the sampling period (usually 1–4 h, depending on the free ammonia concentration expected), the sorbed ammonia is washed from the tube and measured potentiometrically with an ammonia probe. The method is tested theoretically and experimentally. The absorption efficiency of the coated tubes is ca. 90%. In samples of room air containing 12–28 μg m^?3, the standard deviation is estimated as 1.0 μg m^?3. In field use, ammonia contents were in the range 0.53–5.0 μg m^?3.     

环氧乙烷胺化制乙醇胺

环氧乙烷选择性胺化制备乙醇胺成为近年来胺化反应的热点课题。乙醇胺主要由氨水法与液氨法两种制备方法合成,它们分属于典型的均相催化与多相催化。本文从热力学、动力学、反应机理等方面对氨水法的研究进展进行了系统地综述,并部分探讨了工业上氨水法的工艺条件。从催化剂的种类、表面酸碱性质以及孔径结构等方面对液氨法的新进展进行了系统地阐述,最后探讨了选择性胺化反应的未来研究方向。     

A new evanescent wave ammonia sensor based on polyaniline composite

A single-mode TE(0)-TM(0) optical planar waveguide ammonia sensor based on polyaniline/polymethyl methacrylate (PANI/PMMA) composite is designed and developed. The sensing properties of the photonic sensor to ammonia at room temperature are studied. A significant change is observed in the guided light output power of the sensor after it is exposed to ammonia gas. The metrological parameters (sensitivity, response time and recovery time) of the sensor are strongly influenced by the interaction length (length of sensing region). Compared with the conventional optical ammonia sensor based on absorption spectroscopy, the integrated optical sensor is more sensitive to ammonia.     

Enantioselective iridium-catalyzed allylic amination of ammonia and convenient ammonia surrogates

Iridium-catalyzed, asymmetric allylation of ammonia as a nucleophile occurs with stereoselectivity to form a symmetric diallylamine, and related allylation of the inexpensive ammonia equivalent potassium trifluoroacetamide or the highly reactive ammonia equivalent lithium di-tert-butyliminodicarboxylate forms a range of conveniently protected, primary, alpha-branched allylic amines in high yields, high branched-to-linear regioselectivities, and high enantiomeric excess. The reactions of ammonia equivalents were conducted with a catalyst generated from a phosphoramidite containing a single stereochemical element.     

介孔炭表面性质对吸附去除低浓度氨性能的影响

室内环境中低浓度氨污染普遍存在,影响人的身体健康,而消除这些低浓度的氨相对困难。本文报道了一种适用于低浓度氨吸附去除的介孔炭材料,其性能明显优于经硝酸处理的活性炭材料。该介孔炭采用磷酸铝为硬模板制备,炭表面存在大量含氧官能团,研究显示炭表面羧基和内酯基在吸附氨过程中发挥着重要作用,它们作为酸性中心与氨发生化学作用,可以有效地捕获空气中低浓度的氨污染物。