Plasma afterglow atomization in electrothermal atomic absorption spectrometry

Potentialities of an Ar/H₂ microwave induced plasma afterglow at 8.2 mbar as an atomization source in electrothermal atomic absorption spectrometry have been examined. More specifically the atomization efficiency, as shown from appearance temperatures, and the reaction mechanisms of the atomization of the oxides and chlorides of alkaline earth and transition metals have been investigated and compared with conventional electrothermal atomization. For all the investigated metal chlorides and alkaline earth oxides, a considerable decrease in appearance temperature (some 500 K), is observed in the plasma afterglow. Such enhanced atomization is believed to be linked to reactions with H atoms. No plasma enhancement, however, is measured for the atomization of the transition metal oxides. All metal oxides are effectively reduced to free metal in the solid state by the Ar/H₂ afterglow, and as a consequence the supply rate is governed by the metal sublimation for these compounds. For metal chlorides, however, strong evidence is found for the atomization process to proceed via gas phase reactions.     

Nickel chloride interferences on zinc and cobalt in graphite furnace atomic absorption spectrometry using a dual cavity platform

The interference mechanisms of nickel chloride in the determination of cobalt and zinc by graphite furnace atomic absorption spectrometry were investigated using a dual cavity platform. This platform, which has two separate cavities instead of one, allows interferences in the gas phase and in the condensed phase to be differentiated by pipetting the analyte and the interferent onto the separate locations as necessary. The interference mechanism of nickel chloride is found to depend upon the pyrolysis temperature. In the presence of excess nickel chloride, analyte chlorides are formed both in the condensed phase and by reaction between analyte species and HCl(g) generated by the hydrolysis of nickel chloride. The analyte chlorides are then lost during pyrolysis or at the very beginning of the atomization step. At low pyrolysis temperatures, where nickel chloride is not significantly hydrolysed, the drop in sensitivity can be attributed to the expulsion of the analyte species together with rapidly expanding decomposition products of nickel chloride, and/or to gas-phase reaction between analyte atoms and chlorine in the atomization step.     

The removal of chloride interference in determination of chromate ion by atomic absorption spectrometry with electrothermal atomization

Two mechanisms of chloride interference in the atomic absorption spectrometry of chromate in a graphite furnace have been established. The first is due to chloride salts remaining at the atomization step; this can be prevented by volatilizing the chlorides or converting them to oxides before atomization. The other arises from formation of chlorochromate ions, which can be removed by addition of an organic acid. The tetraammonium salt of EDTA is very suitable for this purpose.     

Matrix Effect of Alkali and Alkaline Earth Metal Halides on Fluorescence Quantum Yield of Indium in Laser‐Induced Fluorescence Flame Spectrometry

As interfered with by alkali and alkaline earth metal halides added as the matrix in an acetylene/air flame, the fluorescence quantum yield of In as the analyte in a laser‐induced fluorescence (LIF) flame spectrometry has been thoroughly characterized. The fluorescence quantum yield is determined by a ratio of F to A, where F is the measured fluorescence of In and A is the difference between the absorption signals recorded for the analyte and the blank solutions. The normalized fluorescence signal is treated to prevent deviations due to variations of the atomization efficiency under the conditions with and without the matrix added. The fluorescence quantum yield is measured to be almost independent of the matrix concentration up to 500 ppm (μg/mL) studied, under conditions of either optical unsaturation or saturation. By considering a quenching effect induced by electron‐atom collisions, the calculated fluorescence quantum yields are consistent with our observations.     

Removal of chloride interference in the determination of chromium by atomic absorption spectrometry with electrothermal atomization

Two mechanisms of chloride interference are described. The first arises from coordination of chloride to chromium(III), which can be prevented by addition of a masking agent such as tetraammonium—EDTA, The other is due to chloride salts remaining at the atomization step; this can be prevented by volatilizing the chlorides or converting them to oxides before atomization.     

Use of 2-(tert-butoxy)-N-(3-carbamothioylphenyl)acetamide and graphene oxide for separation and preconcentration of Fe(Ⅲ),Ni(Ⅱ),Cu(Ⅱ) and Zn(Ⅱ) ions in different samples

A simple and selective method using a column packed with graphene oxide(GO) as a solid phase extractant has been developed for the multi-element preconcentration of Fe(Ⅲ),Ni(Ⅱ),Cu(Ⅱ) and Zn(Ⅱ)ions prior to flame atomic absorption spectrometric determinations.The method is based on the sorption of mentioned ions on synthesized GO using 2-(tert-butoxy)-N-(3-carbamothioylphenyl)acetamide as a chelating agent.Several parameters on the extraction and complex formation were optimized.Under the optimized conditions(pH 6,flow rate 9 mL/min),metal ions were retained on the column,then quantitatively eluted by HNO3solution(5 mL,3.0 mol/L).The preconcentration factor was calculated as250.The detection limits for the analyte ions of interest were found in the range of 0.11 ng/mL(Ni2+) to0.63 ng/mL(Cu2+).The column packed with GO was adequate for metal ions separation in matrixes containing alkali,alkaline earth,transition and heavy metal ions.     

Studies on the occurrence of atoms and molecules of aluminum, gallium, indium and their monohalides in an electrothermal carbon furnace

Molecular absorption spectra of monohalides (MX; X = F, Cl and Br) of aluminum, gallium and indium have been observed, where the monohalide species were produced in the electrothermal carbon furnace. In the spectra, some characteristic band structures have been identified for each metal halide. Generally, aluminum halides and/or metal fluorides provided clear and sharp band structures. The spectral bandwidth, background absorptions, and co-existing cations influenced the analytical features of molecular absorption spectrometry utilizing the monohalide bands. The time-dependent signal profiles of atoms and molecules at the stage of atomization in the carbon furnace have been observed for discussing the mechanisms of atomization and molecule formation of the Group III elements. Alkali and alkaline earth ions enhanced the molecular absorptions of monohalides, and transition metal ions reduced the background absorptions due to cutting the oxide. In addition, the application of the molecular absorptions of monohalides to the determination of trace halogens has also been investigated using the electrothermal vaporization technique.     

A possible steady state kinetic model for the atomization process during flame atomic spectrometry: Application to atomization interference effects of aluminum on Group II elements

The atomization interference effects of AlCl₃ on MgCl₂ and CaCl₂ during flame atomic absorption spectrometry were studied in terms of a steady state kinetic model which takes into account relative rates of thermal dissociation of analyte and interferant metal salts, recombination of counter atom and analyte and interferant atoms, charge transfer between analyte and interferant species, and ion/electron collisional de-ionization within the plasma. Data are presented showing that the interference of AlCl₃ on the atomization of MgCl₂ and CaCl₂ in an air-acetylene flame is due (a) to interference effects due to AlCl₃ which occur prior to complete atomization of the Group II metal chlorides, and (b) to the recombination of the Group II metal and the chlorine atom which is enhanced by the increased density of the chlorine atom as a result of the dissociation of the AlCl₃ interferant.     

A possible steady state kinetic model for the atomization process during flame atomic spectrometry: Application to atomization interference effects of aluminum on Group II elements

The atomization interference effects of AlCl₃ on MgCl₂ and CaCl₂ during flame atomic absorption spectrometry were studied in terms of a steady state kinetic model which takes into account relative rates of thermal dissociation of analyte and interferant metal salts, recombination of counter atom and analyte and interferant atoms, charge transfer between analyte and interferant species, and ion/electron collisional de-ionization within the plasma. Data are presented showing that the interference of AlCl₃ on the atomization of MgCl₂ and CaCl₂ in an air-acetylene flame is due (a) to interference effects due to AlCl₃ which occur prior to complete atomization of the Group II metal chlorides, and (b) to the recombination of the Group II metal and the chlorine atom which is enhanced by the increased density of the chlorine atom as a result of the dissociation of the AlCl₃ interferant. Received: 23 February 1998 / Revised: 18 December 1998 / Accepted: 25 December 1998     

Reaction of polyvinyl chloride with calcium and magnesium oxides

Reaction of polyvinyl chloride with calcium and magnesium oxides was studied. The dependence of binding with metal oxides of hydrogen chloride formed by polyvinyl chloride dehydrochlorination on the oxide to polymer weight ratio and on temperature was examined. The activation energies and specific rates of formation of the corresponding metal chlorides were calculated. Conditions of complete chloride binding into environmentally safe products were found.     

Investigation of interference mechanisms of nickel chloride on copper determination and of colloidal palladium as modifier in electrothermal atomic absorption spectrometry using a dual cavity platform

The interference of nickel chloride on the determination of copper by electrothermal atomic absorption spectrometry was investigated using a specially designed dual cavity platform (DCP), which allows the analyte and interferent to vaporize from separate cavities, so that gas and condensed phase interferences can be distinguished to some extent. It was found that, when low pyrolysis temperatures were used, the interference of nickel chloride on copper originated from the formation of copper chloride in the condensed phase, which is not efficiently dissociated in the atomization stage. Alternately, when analyte and interferent were in separate cavities of the DCP, a gas-phase reaction between copper and chlorine in the atomization stage resulted in a similar signal depression. When higher pyrolysis temperatures were used, interference could be attributed to losses of volatile copper chloride in the pyrolysis stage. These losses were more pronounced when analyte and interferent were in separate cavities of the DCP, indicating again a gas-phase reaction between copper and chlorine, as well as a protective action of nickel oxide, when analyte and interferent were mixed. Colloidal palladium used as modifier removed the chloride interference independent of the pyrolysis temperature applied, when copper and nickel chloride were mixed. Colloidal palladium also increased the integrated absorbance for copper by 40–50%, even when analyte and modifier were in separate cavities of the DCP, indicating a strong gas-phase interaction between copper atoms and the modifier through adsorption/desorption processes.     

Basicities of alumina-supported alkaline earth metal oxides

A series of alumina-supported alkaline earth metal oxide catalysts were prepared by incipient-wetness impregnation. These catalysts were characterized by nitrogen-sorption to determine their surface areas and pore size distributions. The basicities of these catalysts were characterized by temperature-programmed desorption of carbon dioxide. The TPD results demonstrate that all of the catalysts have one-peak profiles. The basicity increases with increasing atomic number of the alkaline earth metal. The alumina-supported alkaline earth oxides exhibit the same basic properties as bulk metal oxides. However, the presence of alumina can increase the mechanical strength of the catalyst, since the alkaline earth oxides have a weak mechanical strength. The basic properties of the catalysts are strongly influenced by the calcination temperature.     

Ionization interference in the acetylene-nitrous oxide flame

The influence of excess cesium upon the atomic line intensities or absorbances in the acetylene-nitrous oxide flame has been investigated for twenty elements with ionization energies up to 8 eV. Volatilization interference has been corrected for. It is shown that true degrees of ionization can be derived from the intensity increase observed upon cesium addition if corrections for incomplete atomization are made and no molecular ions are formed.     

SCR烟气脱硝对PM2.5排放特性的影响机制研究

采用V₂O₅-WO₃/TiO₂催化剂,对选择性催化还原(SCR)烟气脱硝装置出口PM_2.5物性进行分析,考察SO₂氧化与PM_2.5形成的关系,并采用原位漫反射红外光谱(DRIFTS)对SCR脱硝过程中NH₄HSO₄的生成及SCR脱硝温度条件下的NH₄HSO₄热稳定性进行了分析研究。结果表明,经SCR脱硝后,亚微米级细颗粒数浓度明显升高,且形貌特征及元素组成发生变化,形成的细颗粒主要为NH₄HSO₄及少量(NH₄)₂SO₄;SCR烟气脱硝对PM_2.5排放特性的影响主要通过以下途径:一是SO₃与SCR烟气脱硝系统中的NH₃、H₂O反应形成;二是SO₃与逃逸的NH₃、H₂O在SCR脱硝装置后续系统发生反应形成硫酸氢铵与硫酸铵;此外还与SO₃和烟气中游离的CaO等碱土金属氧化物反应形成硫酸盐,随烟气携带出SCR脱硝装置有关。     

On the mechanism of the releasing effect of lanthanum chloride in flame spectrometry

Graphite furnace volatilization and flame atomization were combined for studying the volatilization characteristics of Ca + Al and Ca + Al + La systems. Based on the results of these model experiments the following mechanism of releasing effect is offered: the excess of lanthanum chloride additive promotes the evolution of calcium chloride vapour at a relatively low temperature and thus the formation of calcium aluminate (the thermostable compound of the analyte and the interferent) is prevented. This explanation is consistent with the finding that a releasing effect is not attained with lanthanum nitrate additive.     

Improvement of the stability of Hg/AC catalysts by CsCl for the high-temperature hydrochlorination of acetylene

Activated carbon-supported mercuric chloride(HgCl_2) is used as an industrial catalyst for acetylene hydrochlorination. However, the characteristic of easy sublimation of HgCl_2 leads to the deactivation o the catalyst. Here, we showed that the thermal stability of the Hg/AC catalyst can be evidently improved when Cs Cl is added into the Hg/AC catalyst. Compared with the pure Hg/AC catalyst, the sublimation rate of HgCl_2 from the Hg–Cs/AC catalyst decreased significantly and the Hg–Cs/AC catalyst showed bette catalytic activity and stability in the reaction. This promoting effect is related to the existence of cesium mercuric chlorides(Cs_xHg_yCl_(x+2y)) highlighted by XRD, HR-TEM and EDX analyses. Thus, reacting HgCl_2 with alkali chlorides to form alkali-mercuric chlorides may be a key to design highly efficient and thermally stable mercuric chloride catalyst for hydrochlorination reactions.     

铝卟啉配合物催化二氧化碳与环氧丙烷共聚反应

铝卟啉是一类土壤环境友好的金属卟啉,尽管早在1978年Inoue就已经发现它可以催化CO₂和环氧丙烷的共聚反应,但是该催化体系一直面临催化活性低、聚合物相对分子质量低等难题。 本文通过改变铝卟啉催化剂配体中苯环上取代基的种类和位置,制备出中心金属电子环境差异化的铝卟啉,并以双三苯基膦氯化铵(PPNCl)为助催化剂,探讨其对CO₂与环氧丙烷的共聚反应的催化行为。 结果表明,当铝卟啉中苯环上2,4位同时被Cl^-取代后,在90 ℃和3 MPa压力下,转化频率(TOF)达到2672 h^-1。 当利用离去能力较强的对甲苯磺酸基团(OTs^-)作为铝卟啉的轴向配体,可以合成出数均相对分子质量达1.84×10⁵的脂肪族聚碳酸酯。     

Disilane Cleavage with Selected Alkali and Alkaline Earth Metal Salts

The industry-scale production of methylchloromonosilanes in the Müller–Rochow Direct Process is accompanied by the formation of a residue, the direct process residue (DPR), comprised of disilanes Me_nSi₂Cl_6-n (n=1–6). Great research efforts have been devoted to the recycling of these disilanes into monosilanes to allow reintroduction into the siloxane production chain. In this work, disilane cleavage by using alkali and alkaline earth metal salts is reported. The reaction with metal hydrides, in particular lithium hydride (LiH), leads to efficient reduction of chlorine containing disilanes but also induces disproportionation into mono- and oligosilanes. Alkali and alkaline earth chlorides, formed in the course of the reduction, specifically induce disproportionation of highly chlorinated disilanes, whereas highly methylated disilanes (n>3) remain unreacted. Nearly quantitative DPR conversion into monosilanes was achieved by using concentrated HCl/ether solutions in the presence of lithium chloride.     

Diesel soot combustion catalysts: review of active phases

The most relevant information about the different active phases that have been studied for the catalytic combustion of soot is reviewed and discussed in this article. Many catalysts have been reported to accelerate soot combustion, including formulations with noble metals, alkaline metals and alkaline earth metals, transition metals that can accomplish redox cycles (V, Mn, Co, Cu, Fe, etc.), and internal transition metals. Platinum catalysts are among those of most interest for practical applications, and an important feature of these catalysts is that sulphur-resistant platinum formulations have been prepared. Some metal oxide-based catalysts also appear to be promising candidates for soot combustion in practical applications, including ceria-based formulations and mixed oxides with perovskite and spinel structures. Some of these metal oxide catalysts produce highly reactive active oxygen species that promote efficient soot combustion. Thermal stability is an important requirement for a soot combustion catalyst, which precludes the practical utilisation of several potential catalysts such as most alkaline metal catalysts, molten salts, and metal chlorides. Some noble metal catalysts are also unstable due to the formation of volatile oxides (ruthenium, iridium, and osmium).     

Size-resolved kinetic measurements of aluminum nanoparticle oxidation with single particle mass spectrometry

Aluminum nanoparticles are being considered as a possible fuel in advanced energetic materials application. Of considerable interest therefore is a knowledge of just how reactive these materials are, and what the effect of size on reactivity is. In this paper we describe results of size resolved oxidation rate using a recently developed quantitative single particle mass spectrometer (SPMS). Aluminum nanoparticles used were either generated by DC Arc discharge or laser ablation, or by use of commercial aluminum nanopowders. These particles were oxidized in an aerosol flow reactor in air for specified various temperatures (25-1100 degrees C), and subsequently sampled by the SPMS. The mass spectra obtained were used to quantitatively determine the elemental composition of individual particles and their size. We found that the reactivity of aluminum nanoparticles is enhanced with decreasing primary particle size. Aluminum nanoparticles produced from the DC Arc, which produced the smallest primary particle size (approximately 19 nm), were found to be the most reactive (approximately 68% aluminum nanoparticles completely oxidized to aluminum oxide at 900 degrees C). In contrast, nanopowders with primary particle size greater than approximately 50 nm were not fully oxidized even at 1100 degrees C (approximately 4%). The absolute rates observed were found to be consistent with an oxide diffusion controlled rate-limiting step. We also determined the size-dependent diffusion-limited rate constants and Arrehenius parameters (activation energy and pre-exponential factor). We found that as the particle size decreases, the rate constant increases and the activation energy decreases. This work provides a quantification of the known pyrophoric nature of fine metal particles.