Determination of volatile bases in seafood using the ammonia ion selective electrode: collaborative study

Nine collaborating laboratories tested a combination of 23 seafood samples for volatile bases using an ammonia ion selective electrode. Results were reported as mg NH3/100 g fish, but the method reflected levels of both ammonia and trimethylamine, which permeated the ammonia membrane. The 23 samples were broken down into 8 blind duplicate pairs, 2 Youden matched pairs, and 3 single samples covering fresh to spoiled product ranging from 8 to 82 mg NH3/100 g. Seven species were evaluated: Atlantic cod, squid, Atlantic halibut, gray sole, monkfish, dogfish, and Atlantic mackerel. The ammonia electrode assay was performed on an aqueous homogenate consisting of 95 mL distilled water and 5.0 g sample tissue. Alkaline ion strength adjusting solution (2 mL) was added to the homogenate to liberate ammonia that was sensed by the ion specific electrode and measured on a precalibrated portable meter. Repeatability standard deviations (RSDr) ranged from 4.2 to 17%; reproducibility standard deviations (RSDR) ranged from 8.8 to 21%. A standard ammonium chloride solution was provided to all laboratories to spike 3 different samples at 10 mg NH3/100 g. Recoveries of added ammonia as ammonium chloride for fresh, borderline, and spoiled samples were 88.6, 107, and 128%, respectively.     

Determination of NH(3) gas by combination of nanosized LaCoO(3) converter with chemiluminescence detector

Combination of a novel NH₃ converter based on nanosized materials with chemiluminescence (CL) detector for the determination of NH₃ gas was demonstrated in this paper. NH₃ gas is oxidized on different nanosized catalysts to produce NO_x, which can react with luminol to generate CL emission. Eight nanosized materials were investigated as catalyst, and CL was detected from seven of them. The nanosized LaCoO₃ was chosen as the catalyst for preparing the converter because of its higher activity than others. Under the optimized conditions, the linear range of CL intensity versus concentration of NH₃ gas is 0.04-10 ppm (r=0.9951, n=14) with the detection limit of 0.014 ppm. The method offers advantages of long lifetime of the converter, fast response and high selectivity to NH₃. There was no response while the foreign substances, such as hydrogen, oxygen, nitrogen, formaldehyde, acetone and gasoline passing through the CL detection system, and the interference of CCl₄, ethanol, ethylene and toluene was insignificant.     

First characterization of the ammine-ammonium complex [(NH4(NH3)4)2(mu-NH3)2]2+ in the crystal structure of [NH4(NH3)4][B(C6H5)4].NH3 and the [NH4(NH3)4]+ complex in [NH4(NH3)4][Ca(NH3)7]As3S6.2NH3 and [NH4(NH3)4][Ba(NH3)8]As3S6.NH3

The compound [NH4(NH3)4][B(C6H5)4].NH3 (1) was prepared by the reaction of NaB(C(6)H(5))(4) with a proton-charged ion-exchange resin in liquid ammonia. [NH(4)(NH(3))(4)][Ca(NH(3))(7)]As(3)S(6).2NH(3) (2) and [NH4(NH3)4][Ba(NH3)8]As3S6.NH3 (3) were synthesized by reduction of As(4)S(4) with Ca and Ba in liquid ammonia. All ammoniates were characterized by low-temperature single-crystal X-ray structure analysis. They were found to contain the ammine-ammonium complex with the maximal possible number of coordinating ammonia molecules, the [NH4(NH3)4]+ ion. 1 contains a special dimer, the [(NH4(NH3)4)2(mu-NH3)2]2+ ion, which is formed by two[NH4(NH3)4]+ ions linked by two ammonia molecules. The H(3)N-H...N hydrogen bonds in all three compounds range from 1.82 to 2.20 A (DHA = Donor-H...Acceptor angles: 156-178 degrees). In 2 and 3, additional H(2)N-H...S bonds to the thioanions are observed, ranging between 2.49 and 3.00 A (DHA angles: 120-175 degrees). Two parallel phenyl rings of the [B(C(6)H(5))(4)](-) anion in 1 form a pi...pi hydrogen bond (C...C distance, 3.38 A; DHA angles, 82 degrees), leading to a dimeric [B(C6H5)4]2(2-) ion.     

Fragmentation of doubly charged ammonia cations NH 3 ++ studied by the photoion-photoion coincidence (PIPICO) method

Doubly charged NH ₃ ⁺⁺ cations were produced by double photoionization of neutral ammonia molecules by using the synchrotron radiation from ACO as a photon source of variable energy in the 35–49 eV energy range. The fragmentation of NH ₃ ⁺⁺ was studied by the photoion-photoion coincidence (PIPICO) method. NH ₃ ⁺⁺ cations were produced in the \(\tilde X^1 \) A ₁ and \(\tilde B^1 \) electronic states of which the onset energies were measured at, respectively, 35.4±0.5 eV and 44.5±0.5 eV. It was shown that the NH ₃ ⁺⁺ ions, initially produced in their \(\tilde X^1 \) A ₁ state, rapidly dissociate (in less than 50 ns), into NH ₂ ⁺ + H⁺. Furthermore, the comparison with results obtained by other methods indicates that NH ₃ ⁺⁺ ions can either be long-lived (τ>10 µs) or slowly dissociating (1 µs<τ<10 µs) or rapidly dissociating (τ<50 ns), depending on their geometry and/or internal energy in their \(\tilde X^1 \) E A ₁ electronic state.     

Determination of nitrate in agricultural material by the nitrate selective electrode

Summary When measuring nitrate in agricultural material (ensilage, dung etc.) extracted with copper sulphate solution with the nitrate selective electrode some of the samples were difficult to measure due to unstable readings and a gradually change in the calibration curve. These problems could easily be reduced by simply diluting the samples before measuring. To the diluted samples standards were added before measurement to keep the readings in the linear part of the calibration curve. In addition this dilution will increase the life time of the electrode.

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Nitratbestimmung in landwirtschaftlichem Material mit Hilfe der Nitrat-selektiven Elektrode

Zusammenfassung Bei der Messung von Nitrat in landwirtschaftlichem Material (Silage, Dung u.a.) mit Hilfe der Nitrat-selektiven Elektrode nach Extraktion mit Kupfersulfatlösung ergaben sich bei einigen Proben Schwierigkeiten wegen instabiler Anzeigen und allmählichen Veränderungen der Eichkurve. Diese Probleme konnten durch einfache Verdünnung vor der Messung reduziert werden. Zu den verdünnten Proben wurden vor der Messung Standards zugesetzt, um die Ablesungen innerhalb des linearen Teils der Eichkurve zu halten. Zusätzlich wird durch die Verdünnung die Lebensdauer der Elektroden erhöht.

     

NMR evidence for two ammonia rotational hindering potentials in solid Ca(NH3)6

Proton spin-lattice relaxation times in Ca(NH₃)₆ have been measured between 10 and 125 K. Three distinct T₁ minima have been observed and are attributed to NH₃ diffusion and to NH₃ rotating in two different hindering potentials. The results suggest that there is an appreciable difference in molecular structure between NH₃ and ND₃ in this compound.     

Coagulation studies for cellulose in the ammonia/ammonium thiocyanate (NH3/NH4SCN) direct solvent system

An extensive study of the coagulation of cellulose from cellulose/ammonia/ammonium thiocyanate solutions is presented. The effect of major variables upon the coagulation process for cellulose solutions is reported. Microscopic observations of the moving boundary associated with the coagulation were performed on gelled cellulose solutions to determine the coagulation rate as a function of molecular volumes of coagulant, bath temperatures, bath compositions, and cellulose concentrations. The data were analyzed by means of a one-dimensional linear diffusion model based on Fick's law, thereby depicting the mechanism of the coagulation process, and obtaining the diffusion coefficients of mobile components involved in the coagulation.     

Proton magnetic resonance in Sr(NH3)6: Evidence for rapid ammonia diffusion

The proton magnetic resonance linewidth in Sr(NH₃)₆ has been measured in the range 40–300 K. Two line-narrowing transitions have been detected as the temperature is increased. Between 40 and 54 K the linewidth decreases from about 2 to 1.6 G, and in the range 97–140 K the line narrows from about 1.6 G to 15 mG. The results are interpreted in terms of proton tunneling at low temperatures, a transition from tunneling to classical rotation of ammonia molecules between 40 and 54 K, and an ammonia diffusional transition with an activation energy of about 3 kcal/mole in the range 97–140 K.     

超声提取-离子选择电极法测定铝渣中的氟化物

目前铝渣中的氟化物对环境的影响已经成为人们关注重点之一。为了能够准确测定铝渣中的氟化物含量,实验对超声时间、固液比以及Al~(3+)和Ca~(2+)同时存在下的干扰进行了研究。确定了最佳超声时间为20min,以固液比为1∶20进行超声提取,提取液移取体积为5mL,加入总离子强度溶液15mL的方法来消除质量浓度不大于25mg/L Al~(3+)和Ca~(2+)的干扰,运用离子选择电极法准确测定铝渣中的氟化物,得到标准曲线线性相关系数为0.999 9,方法检出限为0.3mg/kg,相对标准偏差(n=6)小于2%,加标回收率在90.8%～108%。同时用超声提取法对样品进行前处理,分别运用离子选择电极法和离子色谱法对铝渣中的氟化物进行测定,两者测定结果一致,方法的准确度良好。     

Infrared predissociation spectroscopy of ammonia cluster cations (NH3)n+ (n=2-4) produced by vacuum-ultraviolet photoionization

Infrared predissociation spectroscopy of vacuum ultraviolet-pumped ion (IRPDS-VUV-PI) is performed on ammonia cluster cations (NH3)n+ (n=2-4) that are produced by VUV photoionization in supersonic jets. The structures of (NH3)2+ and (NH3)4+ are determined through the observation of infrared spectra and vibrational calculations based on ab initio calculations at the MP2/6-31G** and 6-31++G** levels. (NH3)2+ is found to be of the "hydrogen-transferred" form having the (H3N+-...NH2) composition. In contrast, (NH3)4+ exhibits the "head-to-head" dimer cation (H3...NH3+ core structure, where the positive charge is shared between two ammonia molecules in the core, and two other molecules are hydrogen bonded onto the core. An unequivocal assignment of the infrared spectrum of (NH3)3+ has not been achieved, because the presence of two isomeric structures could be suggested by the observed spectrum and theoretical calculations.     

Isotopic exchange of gaseous ammonia 14NH3 and 15NH3 in sulfonated macroreticular ion exchangers

Adsorption and ¹⁵NH₃ isotopic exchange was performed on dry macroreticular polystyrene ion exchanges crosslinked with varying amounts of divinylbenzene and partially neutralized by ¹⁴NH₃. Data on pressure changes and mass spectrometric analyses of isotopic composition of the gaseous phase were used to calculate equilibrium distribution of ¹⁴NH₃ and ¹⁵NH₃ under various dislocation conditions. It was established that along with the exchange of ¹⁴NH₃ to a gaseous phase, ¹⁵NH₃ penetrates to the mass of ion exchanger. This is evidently due to the migration of ammonia among functional groups. It was found that by thermal desorption under reduced pressure ammonia is released only from functional groups located on the surface of ion exchanger.     

Zwei Galliumfluorid-Ammoniakate: Ga(NH3)F3 und Ga(NH3)2F3

Two Gallium Fluoride Ammine Complexes: Ga(NH₃)F₃ and Ga(NH₃)₂F₃ Two gallium trifluoride ammines, Ga(NH₃)F₃ and Ga(NH₃)₂F₃, are obtained as single crystals through oxidation of gallium metal with NH₄HF₂ (Ga : NH₄HF₂ = 1 : 1.5) and NH₄F (Ga : NH₄F = 1 : 3.5), respectively, at 450 °C and 400 °C. Ga(NH₃)F₃ crystallizes with the non-centrosymmetric space group Abm2 (a = b = 544.6(2) pm, c = 986.6(4) pm) forming two-dimensional layers of [Ga(NH₃)F₅] octahedra. The addition of another NH₃ molecule in Ga(NH₃)₂F₃ (orthorhombic, Immm, a = 700.0(3) pm, b = 724.7(2) pm, c = 393.1(1) pm) leads to one-dimensional rods of [Ga(NH₃)₂F₄] octahedra running parallel [001] which are stacked in the [010] direction. Infrared spectra suggest hydrogen bonding (N–H…F) in Ga(NH₃)F₃, for Ga(NH₃)₂F₃ an unequivocal statement is not possible.     

Isothermal pyrolysis of iodomethanes in gases

The fact was established that the pyrolysis of gaseous iodomethanes RI yields methane and non traces of recombination products R2. A pyrolysis mechanism was proposed and rate constants of limiting stages of the pyrolysis of iodomethane, trideuteroiodomethane, and diiodomethane over the range of 500–1500 K were determined.     

Zwei neue Ammoniakate des Scandiumtrichlorides,ScCl3(NH3) und ScCl3(NH3)2

Two New Ammoniates of Scandium Trichloride, ScCl₃(NH₃) and ScCl₃(NH₃)₂ Reactions of scandium with ammonium chloride in the presence of cupric chloride in sealed copper ampoules yield colorless single crystals of the two new ammoniates of scandium trichloride, ScCl₃(NH₃) und ScCl₃(NH₃)₂. The crystal structures were determined from single crystal data; they both crystallize with the triclinic crystal system. In ScCl₃(NH₃)₂ isolated unsymmetrical dimers of double octahedra, according to [Sc‐mer‐(NH₃)_3/1Cl_1/1Cl_(2/2)×2Sc(NH₃)_1/1Cl_3/1] are the characteristic structural features. The crystal structure of ScCl₃(NH₃) also contains double octahedra, [Sc(NH₃)_2/1Cl_2/1Cl_2/2]₂; these dimers are, however, connected via common edges forming infinite zig‐zag chains according to the formulation [Sc(NH₃)_1/1Cl_1/1Cl_4/2].     

Crystal Structure of Ni(NH3)Cl2 and Ni(NH3)Br2

Ni(NH₃)Cl₂ and Ni(NH₃)Br₂ were prepared by the reaction of Ni(NH₃)₂X₂ with NiX₂ at 350 °C in a steel autoclave. The crystal structures were determined by X‐ray powder diffraction using synchrotron radiation and refined by Rietveld methods. Ni(NH₃)Cl₂ and Ni(NH₃)Br₂ are isotypic and crystallize in the space group I2/m with Z = 8 and for Ni(NH₃)Cl₂: a = 14.8976(3) Å, b = 3.56251(6) Å, c = 13.9229(3) Å, β = 106.301(1)°; Ni(NH₃)Br₂: a = 15.5764(1) Å, b = 3.74346(3) Å, c = 14.4224(1) Å, β = 105.894(1)°. The crystal structures are built up by two crystallographically distinct but chemically mostly equivalent polymeric octahedra double chains [NiX_3/3X_2/2(NH₃)] (X = Cl, Br) running along the short b‐axis. The octahedra NiX₅NH₃ share common edges therein. The crystal structures of the ammines Ni(NH₃)_mX₂ with m = 1, 2, 6 can be derived from that of the halides NiX₂ (X = Cl, Br) by successive fragmentation of its CdCl₂ like layers by NH₃.     

Phase transitions in perovskite-like oxyfluorides (NH4)3WO3F3 and (NH4)3TiOF5

Calorimetric and X-ray measurements have been performed on ammonium oxyfluorides (NH₄)₃WO₃F₃ and (NH₄)₃TiOF₅ from 120 up to 300 K. Two and one structural phase transitions were found for the former and latter compounds, respectively. In accordance with the entropy parameters both compounds undergo phase transitions of order–disorder type.     

Determination of phosphorous in titanium bearing minerals by potentiometric titration using Pb-ion selective electrode

A method for phosphorous determination in titanium bearing minerals by potentiometric titration using a Pb-ion selective electrode has been developed. Sample decomposition is achieved by means of K(2)CO(3) fusion in a platinum crucible at 800 degrees C for 30 min in a muffle furnace, and subsequent leaching with water of the fused melt. The aqueous leachate is neutralised with HClO(4) and subsequent boiling. The obtained solution is used for titration with Pb(ClO(4))(2), and the Pb-ion selective electrode detects the end point. The lowest concentration determinable is 0.02% P(2)O(5) in a solid sample. The method was applied on in-house titanium bearing mineral samples and on IGS-31 ilmenite sample (British Geological Survey, UK). Synthetic samples were prepared and analysed, and phosphorous recovery is in the range 98-106%. The recovery and accuracy of the present method have been validated by spiking experiments and by comparing with the spectrophotometric values, respectively. The precision of the proposed method in terms of relative standard deviation is 2.0%.