Updating chromatographic predictions by accounting ageing for single and tandem columns

The most efficient optimization methodologies in liquid chromatography are based on the modeling and prediction of the chromatographic behavior for each compound in the sample. However, when the column suffers some ageing after the modeling process, predictions may differ significantly from the actual separation. Repeating the modeling is especially troublesome when several columns are involved, as is the case of coupled columns. We propose a shortcut to correct the time and peak profiles in these situations, after evaluating the effects of ageing. The original models are corrected by introducing parameters accounting for column ageing, obtained using the data of a small subset of compounds from those used to model the brand‐new column. The ageing parameters are fitted from the discrepancies between the data predicted with the original retention models for the brand‐new column and the experimental data measured for the aged column. The approach was developed and tested to predict the chromatographic behavior of 15 sulfonamides, analyzed with individual and tandem columns, using isocratic and gradient elution. Chromatograms more in line with the aged column performance were predicted. The agreement between predictions and experimental data in the aged columns was excellent.     

Preparation of Alumina Supported Palladium Catalysts by Sol-Gel Method

The chemical reactivity of the aluminium-sec-butoxide (ASB) and the palladium acetylacetonate Pd(acac)₂, used as precursors for the preparation of the alumina supported palladium catalysts by sol-gel method was investigated by the spectroscopic study of the precursor mixture during ageing, using FTIR, UV-VIS and ²⁷Al NMR. The obtaind results showed that acetylacetonate ligands were linked to aluminum when the mixture was aged at 40°C. This was proved by the bands observed at 1530 and 1600 cm^–1 in the FTIR spectra, the band obtained at 289 nm in the UV-VIS spectra and the ²⁷Al NMR sharp peak at 3 ppm. Furthermore, in order to avoid the Pd(acac)₂ reduction to metallic palladium by the SB occurring when the mixture is aged for 3 h, an optimum ageing time should be selected. The precursors modification and the preservation of the palladium oxidation state during ageing could be the required conditions to create a bond between palladium and aluminium during the gelation step. This should be the reason of the thermal stability improvement of the alumina supported palladium catalyst prepared by the sol-gel method.     

Effect of additives on sintering of zirconia ceramics

The effect of two types of additives on the sintering processes of zirconium ceramics was investigated. The impact of both polyvinyl alcohol (12 mass%) and bismuth oxide (1 mass%) on compaction of ultradisperse powders of stabilized zirconia produced by plasma-chemical method and on densification of the compacts during sintering was studied. In the initial state, plasma-chemical powders demonstrate hindered compactibility and sinterability. The additives were incorporated through mechanical stirring with intermediate sieving using a sieve. It was found that introduction of polyvinyl alcohol significantly reduces wall friction and hence facilitates the compaction process. However, no effect on densification and sintering kinetics was observed. Incorporation of bismuth oxide microadditives decreases the temperature of the peak compacting rate. In one-step sintering, the compacts are found to markedly expand at the isothermal ageing stage. The expansion is more distinct at increased compaction pressure. It is shown that this expansion is associated with an increase in the volume of pores surrounded by the liquid phase of bismuth oxide. Two-step sintering with an intermediate stage of isothermal ageing at 1200 °C shows a 100 °C decrease in the sintering temperature, no expansion of the samples occurs at the final ageing stage at sintering temperature, and the ceramics produced exhibits good operational parameters. Recommendations are given on the use of low-melting microadditives in sintering ultradisperse powders obtained by plasma-chemical method.     

Combinatorial synthesis of oxide powders with an autopipetting system

We describe development of a relatively simple, rapid route to produce combinatorial compositional oxide powder libraries by autopipetting of liquid precursors. This partitioning approach should apply equally well to any low viscosity, liquid precursors for the synthesis of oxide powders. A commercial autopipet is modified by fitting a plastic "mask" assembly beneath the pipet array in order to partition and direct liquids into crucibles. A series of 10 mixtures from two precursor solutions can be produced quickly. After they are dispensed, the liquid mixtures are dried in the crucibles and reacted at elevated temperatures to produce oxide powders. In the present work, the viability of the pipetting process is demonstrated by using a polymerizable complex powder synthesis method to produce (1-x) LaAlO(3) - x SrTiO(3) powders. For this system, a reaction at 900 degrees C for 2 h in air was sufficient to yield solid solutions in this system. X-ray powder diffraction was used to determine the pseudocubic unit cell lattice parameter. The linear change of lattice constant with composition confirms the compositional accuracy of the partitioning.     

Voltammetric characterization of metal sulfide particles and nanoparticles in model solutions and natural waters

Voltammetric scans in sulfidic natural waters often reveal reduction peaks in the range −0.9 to −1.35 V versus Ag/AgCl. These peaks have been attributed to iron sulfide complexes or clusters. However, sols containing CuS nanoparticles now also are known to produce reduction peaks in this range. Here we investigate the voltammetric behavior of two additional metal sulfides at the Hg electrode in 0.55 M NaCl + 0.03 M NaHCO₃ electrolyte, pH = 8.5. We show that Pb and Hg sulfides, either as suspended powders or as precipitated nanoparticles, also yield cathodic peaks between −0.9 and −1.35 V, similar to peaks obtained with CuS and FeS. For precipitated nanoparticles, the position and shape of these reduction peaks change with ageing. Freshly formed nanoparticles produce less negative reduction peaks than aged nanoparticles. Peaks from aged nanoparticles often consist of two or more superimposed reduction peaks. When all other experimental parameters are held constant, the amount of nanoparticle analyte accumulated on the electrode increases with the amount of ageing (≤1 h). Addition of EDTA or acidification followed by purging can be used to distinguish PbS nanoparticles and Fe sulfide clusters from CuS and HgS nanoparticles or from colloidal S. This test was applied to interpret −0.9 to −1.35 V reduction peaks observed in two meromictic lakes. In conjunction with other evidence, this test suggests that FeS clusters are present in one case whereas colloidal S is present in the other. Interpreting −0.9 to −1.35 V voltammetric peaks observed in sulfidic natural waters requires caution, but these peaks are potentially rich sources of information about trace metal speciation.     

Determination of E-2-nonenal by high-performance liquid chromatography with UV detection assay for the evaluation of beer ageing

The analysis of E-2-nonenal is of considerable interest for the brewery industry as this compound is claimed to be responsible for a paper/cardboard unpleasant flavour. Usually, the presence of E-2-nonenal can be noticed in aged beers at levels higher than 0.1 microg/l. In this work, an analytical method was developed to determine E-2-nonenal in beer involving steam distillation of beer followed by an extraction/concentration step using solid-phase extraction and determination of E-2-nonenal by HPLC with UV detection. Fastness and simplicity are the main advantages of the proposed method, when compared with other existing methodologies for the determination of E-2-nonenal in beer. Using the developed conditions, the interference of E-2-nonenal formed by degradation of its precursors during steam distillation is almost negligible. The presence of sulphur dioxide at legal levels does not interfere with the assay. The method was used in a comparative study of fresh and either naturally or forced aged beers. A much larger chromatographic peak was found near the peak of E-2-nonenal that correlates well with the peak of E-2-nonenal. Identification of the corresponding compound is currently under investigation, considering its future application on the evaluation of beer ageing.     

Thermal decomposition behaviour of cobalt(II)-picolyl-terminated poly(dimethylsiloxane)

Thermal, chemical and rheological properties of ultraviolet aged asphalt binder were characterized by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) and dynamic shear rheometer (DSR), respectively. Asphalt binder samples were made with different film thickness (50, 100, 200 and 500 μm) and suffered different ageing time (0, 48, 96 and 144 h), at a certain UV radiant intensity of 20 w m^–2 in a self-made accelerated ageing oven. The results indicate that the UV light ageing would lead to the improvement of thermal behavior and the growth of the glass transition temperature of asphalt binder. This type of ageing can be also reflected from the FTIR spectra in terms of the characteristic peaks of the carbonyl groups and sulphoxides. The UV light ageing can change some rheological parameters of asphalt binder, such as complex modulus and phase angle. The ageing degrees of asphalt binder by this type of ageing test are mainly related to the ageing time and film thickness of the sample.     

纳米晶Sb掺杂SnO2(ATO)粉体的合成与表征

以Sn粉和Sb₂O₃为原料.采用共沉淀法制备了纳米ATO粉.TG-DSC及FTIR结果表明.450℃以前前驱体已失去全部水分.并完全转化为氧化物.XRD测量结果表明.所得ATO粉具有四方金红石结构.500℃焙烧后粉体的粒径为12nm.随着焙烧温度的升高.粉体的粒径增加.TEM测定结果表明,粉体的分散性很好.团聚很少.粉体的烧结性能良好,950℃时烧结5h即达到理论密度的97.3％.用霍尔系数法测定粉体的导电行为.表明该粉体具有良好的导电性能.     

New Method for Catalyst Powder Manufacturing Based on Solvent Combustion

A new method for the synthesis of fine catalyst powders is presented. Catalyst precursors are dissolved in an ethanol-water mixture which is burned through a nozzle-type burner. As a result, catalyst powders are formed and removed from flue gases through a filter. LaMnO₃ catalysts for the catalytic combustion of methane have been prepared, characterised (TEM, XRD) and compared with a reference manfacturing method (the citrates one) showing promising, though improvable, results. This revised version was published online in August 2006 with corrections to the Cover Date.     

Protection of natural rubber films against thermal ageing by addition of amine and phenolic anti-oxidants

The aim of the investigation was to discover how to protect natural rubber articles against thermal ageing. Thin films (0.2 mm) were prepared from natural rubber latex by cold dipping and then vulcanized at 100° for 20 min. Films of one series were protected by the addition of amine anti-oxidant, and those of the other series by phenolic anti-oxidant. The films were air aged at 70° for 72 hr or sterilized for or 1 or 2 hr at 120° in sterilization chambers with steam. Breaking strength of films increased by adding the phenolic anti-oxidant up to 1.6 phr, and by adding the quinoline anti-oxidant up to 1.2 phr. Major decrease of breaking strengths occurred in steam ageing. Moduli at 100 and 300% elongation of aged films showed slight stiffening of the rubber. Measurements of elongations at break revealed increased values, especially for prolonged steam sterilizations. Colour developed on ageing was more pronounced in quinoline—containing films and increased in the order: air ageing < steam ageing, 1 hr < steam ageing, 2 hr     

pH值对溶剂热合成FeS2粉体的影响

采用FeSO₄与NH₂CSNH₂为反应前驱物, 通过溶剂热反应合成了高纯度的FeS₂ (pyrite)粉体. 实验表明,在聚乙烯吡咯烷酮（PVP）作保护剂的乙醇水溶液中, 200 ℃下反应36 h, 适当调节溶液的pH值, 即可在酸性环境(pH=5)和碱性环境(pH=10)下制得单一相的黄铁矿型FeS₂粉体. 讨论了溶液pH值对溶剂热合成FeS₂粉体物相组成、晶粒度及光学性质的影响.     

Micrometric BN powders used as catalyst support: influence of the precursor on the properties of the BN ceramic

Thin powders and foams of boron nitride have been prepared from molecular precursors for use as noble metal supports in the catalytic conversion of methane. Different precursors originating from borazines have been tested. The best results were obtained using a precursor derived from trichloroborazine (TCB) which, after reacting with ammonia at room temperature and then thermolyzing up to 1800°C, led to BN powders with a specific area of more than 300 m² g⁻¹ and a micrometric spherical texture. Comparable results were obtained using polyborazylene under similar conditions. Aminoborazine-derived precursors did not yield such high specific area ceramics but the BN microstructure resembled a foam with a crystallized skin and amorphous internal part. These differences were related to the chemical mechanism of the conversion of the precursor into BN. Polyhaloborazines and polyborazines yielded BN through gas-solid reactions whereas aminoborazine polymers could be kept waxy up to high temperatures, which favored the glassy foam. Catalysts composed of BN support and platinum have been prepared using two routes: from a mixture of precursor or by impregnation of a BN powder leading to very different catalysts.     

Oxidation States of Iron in Doped TiO2-SiO2 Sol-Gel Powders: A 57Fe Mössbauer Study

Ceramic coatings obtained by sol-gel routes are more and more attractive for protective purposes. Improved resistance against wet corrosion of steels can be obtained by doping the covering layer with elements like for instance transition ones. It is of major importance to have a clear-cut knowledge of the oxidation state of the doping element, especially after different heat treatments which usually follow the deposition process. Here we report about the oxidation states of 5 wt.% iron doped TiO₂, SiO₂ and mixed sol powders obtained by the sol-gel method with alkoxide precursors added with FeSO₄, 7 H₂O in organic medium. The evolution of the Fe oxidation state versus various heat treatments is followed by ⁵⁷Fe Mössbauer spectrometry supplemented by XRD data. As-dried samples are amorphous and contain ferric Fe cations, with a local distorted oxygen environment. After heating at 500°C during 3 min, ferrous and ferric oxides are evidenced together solely for silica and mixed silica-titania powders, in marked contrast with titania powders where only ferric species exist. The complete ferric state is restored for all samples after annealing at 900°C for one hour.     

低压合成甲醇催化剂母料变色点性质的研究

研究了合成甲醇催化剂母料陈化期间pH值的变化情况，尤其是母料变色点前后pH值的变化，考察了反应pH值及反应温度对变色时间及催化剂活性的影响。结果表明，合成甲醇催化剂母料在陈化期间pH值一直在改变，在变色点附近出现了pH值的一个极小值，与其相应的是在母料变色前后催化剂的活性发生了明显的变化，因此，在变色点前后母料的组成及结构都发生了明显的变化。升高反应温度有利于母料结构的调变，升高反应pH值不利于母料结构的这种变化。通过本实验确定了催化剂母料在并流情况下最佳沉淀pH值范围为7.5～8.5，最佳沉淀温度大于80 ℃。     

Use of Chelate Complexes of Lead(II) in Low-Temperature Technologies of Ceramic Piezoelectric Materials

Technology is suggested for fabrication of ceramic piezoelectric materials from the lead-containing ferroelectric phase. The technology includes a low-temperature synthesis of ultradispersed lead titanate and zirconate powders and also of phases of solid solutions on their basis and the low-temperature procedure for sintering of ceramic fabricated from ultradispersed powders of ferroelectric phases. As precursors used in the suggested low-temperature synthesis serve lead glycerate and tartrate. It was found that, when interacting (at temperatures of 240–330°C) with hydroxo-peroxo-aqua complexes of titanium and(or) zirconium(IV) in the course of 30–40 min, the precursors form ultradispersed powders of these phases, which are single-phase and contain particles with average size of less than 100 nm. It was shown that using the suggested technology makes it possible not only to reduce the energy expenditure for separate procedures for synthesis of ultradispersed ferroelectric phases and for synthesis of piezoelectric materials, but also to substantially diminish the discharge of lead(II) compounds into the atmosphere of industrial premises. It was also shown that the technology enables fabrication of piezoelectric materials with prescribed values of electrical parameters.

     

氧化铝胶体的添加对氧化铝γ→α相变的影响

在γ-Al2O3粉体中添加氧化铝胶体,研究其对氧化铝α相变的影响.结果表明,与α氧化铝粉体籽晶相比较,氧化铝胶体也可以起到籽晶的作用;由于其颗粒较小、在γ-Al2O3中分散均匀且能与之紧密接触,大大降低了α相变温度,改善了煅烧产物的微结构,从而得到分散均匀、平均粒径< 100 nm的α氧化铝超细粉体.根据对粉体形貌TEM的观察,初步探讨了添加氧化铝胶体的前驱体α相变的过程.     

Hydrothermal Synthesis and Characterization of Perovskite PbTiO_3 Powders from Different Precursors

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Low-Density Forsterite (Mg2SiO4) Powders Prepared from Modified Alkoxides

2MgO-SiO₂ low-density powders have been prepared from alkoxide precursors modified with acetic anhydride. The resultant solutions did not gel, but formed precipitates. These consisted of an organic magnesium compound and amorphous silica. Tapping densities comparable with those of forsterite aerogels were obtained, with the density increasing as the precursor solution concentration increased. Crystalline forsterite formed around 790°C. Higher initial solution concentrations led to greater amounts of MgO in the powders after heating to 1000°C. Transmission electron microscopy showed primary particles between 20 and 30 nm which formed loose fractal agglomerates. By altering the preparation conditions, powders with morphologies more like aerogels than xerogels could be produced.     

The mechanical properties of a model hydrogenated nitrile butadiene rubber (HNBR) following simulated sweet oil exposure at elevated temperature and pressure

A typical carbon black reinforced hydrogenated nitrile butadiene rubber (HNBR) was exposed to a mix of hydrocarbons (toluene, heptane and cyclohexane) at elevated temperatures and pressure in order to chemically age the material. The effect of this exposure on the mechanical properties is reported; the most significant change is a dramatic increase in tensile stiffness for specimens exposed at 160 °C for 12 weeks. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) revealed changes in the glass transition behaviour of this material, with a general reduction in the magnitude of the glass transition with increasing ageing time. In addition, gravimetric studies of the swollen specimens after removal from the hydrocarbon mix showed that the more aged specimens underwent significantly slower drying rates compared to less aged specimens. These results may be explained by an increase in crosslink density in the materials being the main mechanism occurring during chemical ageing of these HNBR compounds.     

Counter-flow liquid injection plasma synthesis of spinel powders

A novel counter-flow liquid injection plasma synthesis (CF-LIPS) reactor has been developed to produce ceramic powders. By using a counter-flow plasma configuration, entrainment of reactant particles into the plasma is improved compared to conventional injection methods. The counter-flow process also creates large recirculation zones which increase the residence time to more than 100 ms as predicted by modeling results [1]. The long residence time ensures complete evaporation and decomposition of precursor particles and complete reactions to the desirable products. Also, the process employs liquid precursors rather than solids, resulting in less contamination of products from unevaporated reactants. Results show that CF LIPS is an excellent method for producing single-phase and spherical spinel powders with a narrow particle size distribution. Particle size increases with increasing precursor concentration based on the synthesis of magnesium aluminate powders. Characterization techniques include X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), X-ray mapping, centrifugal sedimentation particle size distribution analysis, and vibrating sample magnetometer (VSM) measurements. In addition, crystallographic studies are conducted to determine the bond lengths, bond angles, and stoichiometries of the as-produced spinels.