Matrix sensitivity of solid sampling AAS. Determination of zinc in geological samples

Direct solid sampling techniques in AAS have several advantages over wet digestion methods such as small sample size requirements and simple calibration procedures. But some disadvantages also exist such as the sample in homogeneity and the matrix sensitivity of calibration. The calibration is commonly carried out by varying the sample mass and evaluating the peak intensity versus absolute analyte amount. It is shown here that this procedure must be considered doubtful when matrix effects are expected. In the case of zinc determination in geological samples it has been shown that calibration functions obtained by different reference materials differ significantly from each other. As an alternative a three-dimensional calibration technique can be applied that evaluates the peak intensity versus both analyte content and sample weight. The resulting calibration planes are expected to be hyperbolically curved. This three-dimensional calibration has been applied to the determination of Zn in geological samples and compared with classical solid sampling AAS calibration procedures.     

Solid solubility in the Bi-Sb-As ternary system

The existence region of the ternary solid solution in the Bi-Sb-As system is studied using DTA, X-ray powder diffraction, and thermodynamic calculations. The alloys of this system have positive nonideality, which is mainly due to the elastic component of the enthalpy of mixing. The nonideality increases as the antimony concentration in the sample decreases, and finally brings about the instability and decay of the solid solution. It is shown experimentally that complete miscibility is observed at high antimony concentrations, when the antimony atom fraction is higher than or equal to 0.75–0.80.     

Properties of molten carboxylates part 6. A quantiative differential thermal analysis study of phase transitions in some zinc and cadmium carboxylates

Quantitative DTA results are presented for the phase changes in some cadmium and zinc n-alkanoates. Cadmium carboxylates form liquid crystal phases. The total entropy of the solid-to-liquid transition is small indicating a high degree of aggregation in the isotropic liquid. The phases previously reported by Skoulios are shown to be due to the presence of basic carboxylates. The zinc carboxylates have solid—solid transformations but do not form liquid crystal phases. The entropies of fusion are of the same order as those in the lead salts showing only a small degree of aggregation in the liquid.     

30 years of research in thermal analysis and calorimetry

The research in thermal analysis and calorimetry, conducted by the author over the period 1964 to 1993, is summarised and concisely reviewed. The major investigations have focussed on thermal analysis studies of coordination compounds, particularly the metal dithiocarbamate complexes. A significant solution calorimetric study of some metal dithiocarbamate complexes has also been undertaken. DSC has been applied to determine the sublimation enthalpies of many metal dithiocarbamate and metal pentane-2,4-dionate complexes and solution calorimetry has been applied to study the thermochemistry of the latter group of complexes. Thermal analysis investigations of several inorganic molten salt systems have been initiated. Thermometric titrimetry has been applied to study metal-macrocyclic ligand systems in aqueous media and particularly those systems of environmental significance. Temperature calibration standards for TMA have been proposed and TMA has been applied to study the mechanical properties of several common inorganic compounds. DTA has been applied to study a wide variety of phenols and has subsequently been applied as an analytical technique to determine the components of solid state phenol mixtures. Thermometric titrimetry has been applied to determine the phenolic content of wines. A comprehensive thermal analysis study of Australian brown coal has been undertaken, involving the DSC determination of coal specific energy, a TG/DTA study of the coal pyrolysis and combustion processes and a TG/DTA and EGA study of the cation catalytic effect on the coal pyrolysis process. Thermal analysis and calorimetric techniques have been extensively publicised and promoted by the publication of specialist reviews, the presentation of symposia review papers and the oral presentation of short courses, particularly in the SE Asian region. This review essentially reveals the diversity of possible application of thermal analysis and calorimetric techniques and the primary significance of thermodynamic data in the fundamental rationalisation of chemical phenomena.     

Preliminary round-robin studies on the ICTAC certified reference materials for DTA

The ICTAC Committee on Standardisation has formed a Task Group to investigate the suitability of the ICTAC Certified Reference Materials for DTA, covering the temperature range 450°–1100°C, for accurate temperature calibration purposes and to evaluate their potential as enthalpy calibrants for DTA and DSC equipment. This paper reports the results of preliminary round-robin studies on barium carbonate and strontium carbonate, using a dual-point calibration method based on the melting points of aluminium and gold. In addition the fusion of ICTAC potassium sulphate has been investigated as a possible calibration transition.     

Dynamic dielectric analysis. A new thermal analysis technique

Applications of dynamic dielectric analysis (DDA) in studies on the thermal decomposition and phase transformations of solid materials are discussed. Three illustrative examples are presented for (a) a system undergoing a chemical reaction or thermal alteration on application of heat, (b) a system undergoing a crystallographic transformation and (c) detection of moisture in naturally occurring materials. The advantages derived by applying a combination of DDA and a conventional thermal analysis technique such as DTA to studies on thermal processes are demonstrated. It is shown that the information obtained from techniques such as DTA or TG is limited in scope unless used in conjunction with a method which sheds light on the mechanistic aspects of the physical or chemical process of interest.     

A study of transition temperature standards by DTA

Thirteen reference standards (TherMetric melting point standards and NBS-ICTA standards) for temperature calibration of DTA in the range from 50 to 425° have been compared and found to be accurate to within ±0.5°. Most of these standards are shown to be usable to at least 100°/min heating rates.     

Applications of inductively coupled plasma mass spectrometry and laser ablation inductively coupled plasma mass spectrometry in materials science

Inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) have been applied as the most important inorganic mass spectrometric techniques having multielemental capability for the characterization of solid samples in materials science. ICP-MS is used for the sensitive determination of trace and ultratrace elements in digested solutions of solid samples or of process chemicals (ultrapure water, acids and organic solutions) for the semiconductor industry with detection limits down to sub-picogram per liter levels. Whereas ICP-MS on solid samples (e.g. high-purity ceramics) sometimes requires time-consuming sample preparation for its application in materials science, and the risk of contamination is a serious drawback, a fast, direct determination of trace elements in solid materials without any sample preparation by LA-ICP-MS is possible. The detection limits for the direct analysis of solid samples by LA-ICP-MS have been determined for many elements down to the nanogram per gram range. A deterioration of detection limits was observed for elements where interferences with polyatomic ions occur. The inherent interference problem can often be solved by applying a double-focusing sector field mass spectrometer at higher mass resolution or by collision-induced reactions of polyatomic ions with a collision gas using an ICP-MS fitted with collision cell. The main problem of LA-ICP-MS is quantification if no suitable standard reference materials with a similar matrix composition are available. The calibration problem in LA-ICP-MS can be solved using on-line solution-based calibration, and different procedures, such as external calibration and standard addition, have been discussed with respect to their application in materials science. The application of isotope dilution in solution-based calibration for trace metal determination in small amounts of noble metals has been developed as a new calibration strategy. This review discusses new analytical developments and possible applications of ICP-MS and LA-ICP-MS for the quantitative determination of trace elements and in surface analysis for materials science.     

A switch-on fluorescence assay for bacterial β-lactamases with amyloid fibrils as fluorescence enhancer and visual tool

Herein is described the development of a novel switch-on fluorescence assay for detecting β-lactamases. The fluorescence assay comprises two components: solid beads coated with a β-lactam antibiotic, which is linked to an environment-sensitive fluorophore (dansylaminothiophenol, DTA), and amyloid fibrils of hen lysozyme (acting as fluorescence enhancer and visual tool). In the presence of the clinically significant TEM-1 β-lactamase, the DTA-antibiotic complex on the solid beads is hydrolyzed, thus releasing the DTA dye into solution. The DTA dye is only weakly fluorescent in solution but gives strong green fluorescence upon binding to lysozyme fibrils. These strongly fluorescent DTA-bound fibrils can be easily visualized by the naked eye upon illumination of the sample with a simple UV lamp. The fluorescence assay can detect TEM-1 at low concentration (0.01 nM). In contrast, no observable fluorescence appears when the fluorescence assay is performed on samples without the TEM-1 β-lactamase.     

Variable interlayer distance of intercalates of naphthalenedisulfonate isomers in hydrotalcite-like Zn and Al layered double-hydroxides

Three isomers of naphthalenedisulfonates (naphthalene-2,6-,-1,5- and -2,7-disulfonates; abbreviated as N26DS, N15DS and N27DS, respectively, and collectively abbreviated as NijDS) are intercalated in the interlayer region of Zn and Al layered double-hydroxides (Zn/Al-LDH). The intercalated products are obtained under weak alkaline conditions as precipitates from reaction mixtures containing one of the isomers and calcined powder prepared by using carbonate-intercalated Zn/Al-LDH. When N26DS or N15DS is intercalated, two solid phases are observed which have different values of basal spacing in powder X-ray diffraction (XRD) patterns, whereas only one phase appears when N27DS is intercalated. The different basal spacing results from one of two alternate orientations taken by the interlayer NijDS. One of the two phases appears exclusively in XRD patterns, although the other is produced together with a by-product. A more closely packed orientation is suggested for the interlayer guest molecules in the latter phase. The solid state chemistry has been investigated using UV visible diffuse reflection (DR) spectroscopy, differential thermal analysis/thermogravimetry (DTA/TG) and X-ray photoelectron spectroscopy (XPS).     

Surface Instability of Serpentine in Aqueous Suspensions

The electrokinetic behavior and stability of aqueous suspensions containing serpentine minerals of different deposits have been studied. Crystallochemical analyses carried out by X-ray diffraction, IR spectroscopy, TEM, DTA/TG, and XRF revealed that all samples are lizardite-type serpentines with a similar chemical composition. It has been determined that the electrokinetic behavior of lizardite aqueous suspensions is mainly a function of the Mg/Si atomic ratio on surface. So, the low isoelectric point observed in some samples has been linked to values of this ratio lower than that of the ideal lizardite (Mg/Si=1.5). Dissolution studies have shown that the removal of Mg cations from the solid at speeds faster than that theoretically expected (Mg/Si=1.5), i.e., incongruent dissolution, is responsible for the enrichment of Si cations on surface. Therefore, it has been clearly established that the surface charge value developed in the lizardite/aqueous electrical interface is a function of the lizardite surface alteration grade. Copyright 2000 Academic Press.     

PMHFP与稀土元素的固态络合物的合成及其性质的研究

本文用“萃取-沉淀法”、“水溶液析出法”合成了稀土(Ⅲ)及Ce(Ⅳ)与螫合剂PMHFP的固态络合物。测定了络合物的组成,研究了紫外、红外光谱、热稳定性以及个别络合物作为核磁共振中的化学位移试剂的可能性。     

Methods of calibration in the direct analysis of solid samples by electrothermal atomic absorption spectrometry

One of the major problems involved in the direct analysis of solid samples by electrothermal atomic absorption spectrometry (ETAAS) lies in the calibration step because non-spectral interference effects are often pronounced. Three standardization techniques have been described and used in solid sampling-ETAAS: (i) standard additions method; (ii) calibration relative to a certified reference material; and (iii) calibration curve technique. However, an adequate statistical evaluation of the uncertainty in the analyte concentration in the solid sample is most frequently neglected, and reported errors may be seriously underestimated. This can be attributed directly to the complexity of the statistical expressions required to accurately account for errors in each of the calibration techniques mentioned above, and the general lack of relevant reference literature. The object of this work has been to develop a computer package which will perform the necessary statistical analyses of solid sampling-ETAAS data; the result is the program “SOLIDS” described here in the form of an electronic publication in Spectrochimica Acta Electronica, the electronic section of Spectrochimica Acta Part B. The program could also be useful in other analytical fields where similar calibration methods are used. The hard copy text, outlining the calibration models and their associated errors, is accompanied by a diskette containing the program, some data files, and a manual. Use of the program is exemplified in the text, with some of the data files discussed included on the diskette which, together with the manual, should enable the reader to become familiarized with the operation of the program, and the results generated.     

Theoretical investigation of the mechanism and dynamics of intramolecular coherent resonance energy transfer in soft molecules: a case study of dithia-anthracenophane

A computational study is conducted on dithia-anthracenophane (DTA), for which there is experimental evidence for coherent resonance energy transfer dynamics, and on dimethylanthracene (DMA), a molecule representing the energy donor and the acceptor in DTA. Electronic excitation energies are calculated by configuration interaction singles (CIS) and time-dependent density functional theory (TD-DFT) methods and are compared to experimental ones. Electronic coupling constants are calculated between two DMAs embedded into the ground-state structure of DTA employing methods based on transition densities. The resulting values of electronic coupling provide a more consistent interpretation of experiments than those based on one-half the level spacing of DTA excitation energies. Solvation effects are studied based on the polarizable continuum model (PCM). Solvent-induced polarization and screening effects are shown to make opposite contributions, and the net electronic coupling is little different from the value in a vacuum. The likelihood of coherent population transfer is assessed on the basis of a recently developed theory of coherent resonance energy transfer. The time scale of bath is shown to have an important role in sustaining the quantum coherence. The combination of quantum chemical and dynamical data suggests that the electronic coupling in DTA is in the range of 50-100 cm(-1). The presence of oscillatory excitation population dynamics can be understood from the picture of polaronic excitation moderately dressed with dispersive vibrational modes. The effect of torsional modulation on the excitation energies of DTA and electronic coupling is examined on the basis of optimized structures with the torsional angle constrained. The result suggests that inelastic effect due to torsional motion cannot be disregarded in DTA.     

DTA,ETA, and TG investigations of Zirconium phosphates of different crystallinity

Interpretation of all thermal effects which occur on heating zirconium phosphates is possible when simultaneous DTA, ETA, and TG is applied. A rapid transition of poorly crystalline zirconium phosphate into normal cubic modification at high temperatures is clearly shown by DTA when amorphous zirconium phosphate is used. In contrast, because of the more rigid crystal lattice, this reaction is only visible in ETA when crystalline preparations are heated.Especially after exchange of protons by cations, some amorphous zirconium phosphates exhibit a second exotherm in DTA. This reaction is believed to depend on growing up of partially crystalline structures.     

The application of DTA to hot corrosion studies of chromium and nickel powders and nimonic 80A

DTA has been successfully employed to study the hot corrosion behaviour of chromium and nickel powders and Nimonic 80A alloy samples in the presence of corrodants such as NaCl and Na₂SO₄. The DTA data indicate a large high-temperature exotherm due to oxidation in air; the onset of oxidation occurs at much lower temperatures when additional oxidants are added. The results also show that NaCl attacks chromium much more aggressively than does either Na₂SO₄ or the salt mixture. The reverse has been observed for nickel, i.e. enhanced corrosion in the presence of Na₂SO₄ and the mixtures. Both Cr and Ni are oxidized to their respective oxides, via chloride formation in the presence of NaCl, and via sulphide formation in the presence of Na₂SO₄. Sodium chromate formation was confirmed with chromium in addition to the above compounds in the presence of sodium salts. On the other hand, the DTA results on Nimonic 80A alloy samples indicate that the corrosion attack is negligible as long as the salt is in the solid form, but once the salt is molten it triggers catastrophic corrosion. The mechanism of hot corrosion is discussed.     

CsxRb1-xYbI3体系相图、结构及荧光光谱研究

用一步合成法对CsxRb_1-xYbI₃体系进行了全组成范围内的合成,采用差热分析和X射线粉末相分析法制作了相图,用体系的荧光光谱进一步验证了相图的可靠性.该体系形成一个既有包晶反应又有类低共熔反应的有限固溶体,包晶反应温度和类低共熔反应温度分别为627℃和371℃.相分析确定了RbYbI₃高温相及三类固溶体的结构:0≤x≤0.5形成以RbYbI₃为基的NH₄CdCl₃型固溶体和以RbYbI₃高温相为基的CaIrO₃型固溶体,0.75≤x≤1.0形成以CsYbI₃为基的GdFeO₃型固溶体.     

Progress in direct solid sampling analysis using line source and high-resolution continuum source electrothermal atomic absorption spectrometry

The literature about direct solid sample analysis of the past 10–15 years using electrothermal atomic absorption spectrometry has been reviewed. It was found that in the vast majority of publications aqueous standards were reported as having been used for calibration after careful program optimization. This means the frequently expressed claim that certified reference materials with a matrix composition and analyte content close to that of the sample have to be used for calibration in solid sample analysis is not confirmed in the more recent literature. There are obviously limitations, and there are examples in the literature where even calibration with certified reference materials did not lead to accurate results. In these cases the problem is typically associated with spectral interferences that cannot be corrected properly by the systems available for conventional line source atomic absorption spectrometry, including Zeeman-effect background correction. Using high-resolution continuum source atomic absorption spectrometry, spectral interferences become visible owing to the display of the spectral environment at both sides of the analytical line at high resolution, which makes program optimization straightforward. Any spectrally continuous background absorption is eliminated automatically, and even rapidly changing background absorption does not cause any artifacts, as measurement and correction of background absorption are truly simultaneous. Any kind of fine-structured background can be eliminated by “subtracting” reference spectra using a least-squares algorithm. Aqueous standards are used for calibration in all published applications of high-resolution continuum source atomic absorption spectrometry to direct solid sample analysis. This contribution is based on a presentation given at the Colloquium for Analytical Atomic Spectroscopy (CANAS ‘07) held March 18–21, 2007 in Constance, Germany.     

Thermal studies on some reactions in the solid-state

The solid-state thermal reactions of 2,6-diamino-4-chloropyrimidine, 3,3-dimethoxybenzidine and of thiosemicarbazide with each of 2-hydroxy-1-naphthaldehyde and 2,4-dihydroxybenzaldehyde in a mole ratio of 1∶1 produced (1+1) condensation products (‘half units’). These solid state reactions have been studied by means of differential thermal analysis (DTA). The products of the reactions were identified using elemental analysis and IR spectroscopy. Some kinetic parameters such as orders and activation energies of the reactions were evaluated form the DTA curves.     

Insights into the Crystallisation Process from Anhydrous,Hydrated and Solvated Crystal Forms of Diatrizoic Acid

Diatrizoic acid (DTA), a clinically used X‐ray contrast agent, crystallises in two hydrated, three anhydrous and nine solvated solid forms, all of which have been characterised by X‐ray crystallography. Single‐crystal neutron structures of DTA dihydrate and monosodium DTA tetrahydrate have been determined. All of the solid‐state structures have been analysed using partial atomic charges and hardness algorithm (PACHA) calculations. Even though in general all DTA crystal forms reveal similar intermolecular interactions, the overall crystal packing differs considerably from form to form. The water of the dihydrate is encapsulated between a pair of host molecules, which calculations reveal to be an extraordinarily stable motif. DTA presents functionalities that enable hydrogen and halogen bonding, and whilst an extended hydrogen‐bonding network is realised in all crystal forms, halogen bonding is not present in the hydrated crystal forms. This is due to the formation of a hydrogen‐bonding network based on individual enclosed water squares, which is not amenable to the concomitant formation of halogen bonds. The main interaction in the solvates involves the carboxylic acid, which corroborates the hypothesis that this strong interaction is the last one to be broken during the crystal desolvation and nucleation process.