Direct determination of Ag,Cu and Ni in solid materials by graphite furnace atomic absorption spectrometry using a specially designed graphite tube

This paper presents first results of a study using a specially designed graphite tube (“ring chamber tube”) for direct solid sample analysis. This tube allowed the introduction of a relatively large amount (up to 10 mg) of solid material into a separate chamber around the middle part of the atomisation volume to avoid any disturbance of the optical light path in the atomisation volume due to the solid material. Graphite tubes without and with pyrolytic coatings have been used. Best results were obtained using low and well-defined ramp rates, long integration times and integration of the absorbance (A.s) signals. The good analytical applicability of this tube is demonstrated by several examples: Ag in gold wire for microelectronics and Cu and Ni in plant material. The results obtained from three different methods of calibration are in good agreement with the certified values. The detection limits reached for the three elements are in the pg-range.     

Temperature calibration of a mass spectrographic evolved gas analysis system

Because of the vacuum used in mass spectrographic evolved gas analysis, the usual effects of temperature lag between actual and apparent sample temperatures are exaggerated. Factors contributing to this temperature difference are discussed. The melting point of various metals in the range 110–1100°C are used to obtain insights and estimates regarding these temperature discrepancies at different heating rates, utilizing a variety of sample holders. In general, if the sample is in good contact with the heated supporting surface, the agreement between the observed and reported equilibrium melting temperatures is good at heating rates of ? ～ 20°C min. At higher heating rates the differences become larger (?10°C) and the effect increases with increasing temperature of melting. For sample holders which are not in good contact with the sample, hot spots can develop at high temperatures due to unequal thermal radiation. Under these circumstances the apparent melting point can be considerably lower than the actual equilibrium temperature and less dependent upon heating rate.     

Observation of infrared free-induction decay and optical nutation signals from nitrous oxide using a current modulated quantum cascade laser

Free induction decay (FID), optical nutation, and rapid passage induced signals in nitrous oxide, under both optically thin and optically thick conditions, have been observed using a rapid current pulse modulation, or chirp, applied to the slow current ramp of a quantum cascade (QC) laser. The variation in optical depth was achieved by increasing the pressure of nitrous oxide in a long path length multipass absorption cell. This allows the variation of optical depth to be achieved over a range of low gas pressures. Since, even at the highest gas pressure used in the cell, the chirp rate of the QC laser is faster than the collisional reorientation time of the molecules, there is minimal collisional damping, allowing a large macroscopic polarization of the molecular dipoles to develop. This is referred to as rapid passage induced polarization. The resultant FID signals are enhanced due to the constructive interference between the field within the gas generated by the slow ramp of the laser (pump), and that of the fast chirp of the laser (probe) signal generated by pulse modulation of the continuously operating QC laser. The FID signals obtained at large optical depth have not been observed previously in the mid-infrared regions, and unusual oscillatory signals have been observed at the highest gas pressures used.     

Square modulated differential thermal analysis

KMnF₃ and DKDP crystals have been studied around their phase transitions using a conduction calorimetry technique where a long periodical square thermal pulse (0.05 K in amplitude) is superposed to a heating or cooling ramp as low as 0.06 K h⁻¹. Specific heat data obtained in the dissipation and relaxation semiperiods of the square pulse become different inside the phase transition interval. The electromotive force developed by the heat fluxmeters at the end of the relaxation semiperiod (underlying signal) is compared with the DTA trace obtained in a second run with the same temperature ramp but without the modulated perturbation. The comparison between the DTA trace and specific heat data obtained in the first run allows us to determine the value of the latent heat and to obtain information about the kinetic of the phase transition.     

DSC And X-Ray Diffraction Coupling

A new technique, that allows simultaneous time-resolved synchrotron X-ray diffraction as a function of temperature (XRDT) and high sensitivity DSC to be carried out in the same apparatus, has been developed. Microcalorimetry and XRDT scans can be performed at any rate between 0.01 and 10°C min^?1 with a 0.01°C temperature resolution in the temperature range, 30–130°C and at lower cooling rates but the same heating rates in the ?30–+30°C range. The use of a single and very small sample (1 to 20 μl) contained in a thin glass capillary for both measurements and simultaneous data collection prevents any temperature shift between recordings and any possible difference in the thermal histories of the samples.     

On-line coupled ion chromatography-ICP-(AES, MS) and electro thermal vaporisation-ICP-MS in use for ultra trace analysis of high purity rhenium

This work presents the benefits of coupling techniques such as Electro Thermal Vaporisation (ETV)-ICP-MS and Ion Chromatography (IC)-ICP-(AES, MS) for ultra trace analysis in a high purity rhenium powder sample. Direct analysis using ICP-AES suffers from poor detection limits and allows trace analysis only above 1 g/g for most analytes. ICP-MS analysis of trace elements is more sensitive, but signal depression caused by the heavy Re-ions limits trace analysis to concentrations of 50–100 ng/g analyte in the solid sample. Coupling Ion Chromatography with ICP-spectrometers, combined with time resolved measurement (IC-ICP-TRM) of the elution signals, was used to enhance the sensitivity of both ICP-AES and ICP-MS. Resulting detection limits are in the very low ng/g to pg/g range. Coupling of ETV and ICP-MS offers the possibility of eliminating the volatile Re₂O₇ matrix by thermal pretreatment and allows ICP-MS measurements without matrix interferences caused by Re. Results from these methods are compared with Glow Discharge Mass Spectrometry (GDMS) analysis, a semiquantitative solid state technique. The results are also compared with the manufacturers' specifications to show the power of modern routine analysis using ICP-AES or FAAS.     

Ramp rate effect on polyimide film properties and morphology

The stress in films of semirigid and rigid polyimides (PIs) on silicon (Si) substrate has been measured in situ during curing using a newly modified bending beam apparatus. By using the apparatus, the onset of residual stress in the initially solvent-rich films has also been investigated. The stress characteristics of the PI films are strongly ramp rate dependent. Different ramp rates result in markedly different stress patterns, thermo-mechanical properties, and film morphologies. The residual stress at room temperature after curing is scattered around 23–31 MPa for the films of pyromellitic dianhydride-4,4′-oxydianiline (PMDA-ODA). For pyromellitic dianhydride-p-phenylenediamine (PMDA-PDA), it systematically increases from ?6 to 28 MPa for ramp rate increasing from 0.5 to 10°C/min. The residual stress is very low in the slowly cured PMDA-PDA films. However, these films have gone through a very high-stress transient state during curing. The maximum transient stress is comparatively higher in the films of PMDA-PDA than in PMDA-ODA. Slowly cured PMDA-PDA films exhibit high structural ordering, high in-plane anisotropy, and low coefficient of thermal expansion. ©1995 John Wiley & Sons, Inc.     

Solid—liquid phase diagrams of mixtures containing substituted phenols and amine mixtures

The thermal decomposition of CaCO₃ was studied under high vacuum by means of both TG and the more recently developed constant decomposition rate thermal analysis (CRTA) which allows the monitoring of both reaction rate and the residual pressure over the sample. The reliability of the kinetic results seems to be much higher with the latter technique which actually allows the reduction of the reaction rate and therefore the heat and mass transfer effects over a broad range of sample size. For instance, it was necessary, by conventional TG started under a vacuum of 2 10^?6 torr with a heating rate of 0.5 K min^?1, to lower the amount of sample to 2 mg in order to obtain the same activation energy as that calculated from CRTA with various samples weighing up to 50 mg. The TG experimental conditions quoted above (and which are upper limits of mass and heating rate) are beyond the limit of sensitivity of most available conventional TG equipment.     

Photothermal microscopy applied to the study of polymer composites

It is proposed to transfer the capabilities of a high sensitivity photothermal technique, developed by the group and widely used in the study of thermal properties of ceramics, metals and glass, to the study of polymer composites. The technique uses a sensing beam for the measurement of the thermal response of the sample due to local effects induced by heating with a modulated pump laser. With a simple spatial sweep of the beams on the sample surface, information on a micrometric scale of the thermal diffusivity of the material, distribution of phases and pores is obtained. Post-process analysis allows calculating average values of relevant properties such as thermal diffusivity, degree of crystallinity and distribution of aggregates. These measurements are performed at low laser powers (of the order of micro watts) avoiding the damage of the studied samples and turning this technique into a powerful tool of non-destructive characterization.     

Electrospray ionization with aluminum foil: A versatile mass spectrometric technique

In this study, we developed a novel electrospray ionization (ESI) technique based on household aluminum foil (Al foil) and demonstated the desirable features and applications of this technique. Al foil can be readily cut and folded into desired configuration for effective ionization and for holding sample solution in bulk to allowing acquisition of durable ion signals. The present technique was demonstrated to be applicable in analysis of a wide variety of samples, ranging from pure chemical and biological compounds, e.g., organic compounds and proteins, to complex samples in liquid, semi-solid, and solid states, e.g., beverages, skincare cream, and herbal medicines. The inert, hydrophobic and impermeable surface of Al foil allows convenient and effective on-target extraction of solid samples and on-target sample clean-up, i.e., removal of salts and detergents from proteins and peptides, extending ESI device from usually only for sample loading and ionization to including sample processing. Moreover, Al foil is an excellent heat-conductor and highly heat-tolerant, permitting direct monitoring of thermal reactions, e.g., thermal denaturation of proteins. Overall, the present study showed that Al-foil ESI could be an economical and versatile method that allows a wide range of applications.     

Birefringence thermal analysis of liquid crystalline monomers and their photopolymers

Birefringence analysis was used to measure thermal transitions in liquid crystal diacrylate monomers and their corresponding polymers. In this technique, linearly polarized light was used to probe the sample as the temperature increased via a linear ramp. Various phase transitions were observed in the liquid crystalline monomers. In addition, the monomers were isothermally photopolymerized in the liquid crystalline state and the resulting polymer networks retained their liquid crystalline order. Glass-to-rubber transitions as well as indications of further thermal polymerization and stress relaxation were detected. Results from birefringence experiments were compared to those of more traditional thermal analysis techniques including DSC and TMA.The authors would like to thank the National Science Foundation for sponsoring this research under NSF Grant No. DMR-9420357. We would also like to thank Mary Galaska and John Murphy, of the University of Dayton, for their help in conducting experiments, and Katy Weaver, also of the University of Dayton, for her help in sample preparation.     

Carbothermal synthesis of vanadium nitride: Kinetics and mechanism

Constant rate thermal analysis (CRTA) has been used for the first time to study the kinetics of the carbothermal reduction of V₂O₅ in nitrogen to obtain vanadium nitride. It is noteworthy to point out that CRTA method allows both a good control of pressure in the sample surroundings and the use of reaction rates low enough to keep temperatures gradients at a negligible level to avoid any heat or mass transfer phenomena. This method allows one to control the texture and the structure of many materials through kinetic control of the thermal treatment of the precursors. The precise control of the external parameters of the reaction shows that CRTA is an attractive method for kinetic studies and leads to more reliable kinetic data. It has been shown that the carbothermal synthesis of vanadium nitride is best described by a three‐dimensional diffusion kinetic model (the Jander equation) with an activation energy which falls in the range of 520–540 kJ/mol. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 369–375, 2006     

Method for rapid tritiated water extraction from environmental samples

We have developed a thermal vacuum desorption process to rapidly extract water from environmental samples for tritium analysis. Thermal vacuum desorption allows for extraction of the moisture from the sample within a few hours in a form and quantity suitable for liquid scintillation counting and allows detection of tritium at the levels of <2 Bq/l of milk, <0.5 Bq/g of vegetation, and <0.5 Bq/g of soil. We developed a prototype unit that can process batches of twenty or more samples within 24 hours. Early data shows that a high percentage of water is extracted reproducibly without enrichment or depletion of the tritium content. The quench coefficient of the extracted water is low allowing for accurate, direct liquid scintillation counting. In most samples, good comparison has been observed with results using freeze-dry lyophilization as the water extraction method     

Influence of the heating rate on the temperature profiles and on the conversion rate of powdery cellulose and pine sawdust

An experimental study of the thermal decomposition of powdered cellulose and pine sawdust has been performed. The influence of the heating rate on the temperature profiles in the sample and on the solid conversion rate has been studied. A mathematical model without adjustable parameters has been used to calculate the temperature at different points in the solid bed and the average total solid conversion. The experimental results have been compared with those calculated by the model. A good agreement has been obtained for sawdust. Some differences are observed for cellulose at high heating rates, and the influence of the thermal conductivity and the reaction heat on the results has been analysed.     

Electrochemical oxidation and cleavage of peptides analyzed with on-line mass spectrometric detection

An on-line electrochemistry/electrospray mass spectrometry system (EC/MS) is described that allows fast analysis of the oxidation products of peptides. A range of peptides was oxidized in an electrochemical cell by application of a potential ramp from 0 to 1.5 V during passage of the sample. Electrochemical oxidation of peptides was found to occur readily when tyrosine was present. Tyrosine was found to be oxidized between 0.5 and 1.0 V to various oxidation products, including peptide fragments formed by hydrolysis at the C-terminal side of tyrosine. The results confirm earlier knowledge on the mechanisms and reaction products of chemical and electrochemical peptide oxidation. Methionine residues are also readily oxidized, but do not induce peptide cleavage. At potentials higher than about 1.1 V, additional oxidation products were observed in some peptides, including loss of 28 Da from the C-terminus and dimerization. The tyrosine-specific cleavage reaction suggests a possible use of the EC/MS system as an on-line protein digestion and peptide mapping system. In addition, the system can be used to distinguish phosphorylated from unphosphorylated tyrosine residues. Four forms of the ZAP-70 peptide ALGADDSYYTAR with both, either or neither tyrosine phosphorylated were subjected to a 0-1.5 V potential ramp. Oxidation of, and cleavage adjacent to, tyrosine was observed exclusively at unphosphorylated tyrosine residues.     

n-alkanes on MgO(100). I. Coverage-dependent desorption kinetics of n-butane

High-quality temperature-programmed desorption (TPD) measurements of n-butane from MgO(100) have been made for a large number of initial butane coverages (0-3.70 ML, ML-monolayers) and a wide range of heating ramp rates (0.3-10 K/s). We present a TPD analysis technique which allows the coverage-dependent desorption energy to be accurately determined by mathematical inversion of a TPD spectrum, assuming only that the preexponential factor (prefactor) is coverage independent. A variational method is used to determine the prefactor that minimizes the difference between a set of simulated TPD spectra and corresponding experimental data. The best fit for butane desorption from MgO is obtained with a prefactor of 10(15.7+/-1.6) s(-1). The desorption energy is 34.9+/-3.4 kJ/mol at 0.5-ML coverage, and varies with coverage approximately as Ed(theta)=34.5+0.566theta+8.37 exp(-theta/0.101). Simulations based on these results can accurately reproduce TPD experiments for submonolayer initial coverages over a wide range of heating ramp rates (0.3-10 K/s). Advantages and limitations of this method are discussed.     

Multi-wavelength thermal lens spectrophotometer

A novel four-wavelength pump-probe configuration thermal lens spectrophotometer that is capable of simultaneously measuring thermal lens signals at four different wavelengths has been developed. The four excitation beams were derived from the same argon ion laser, which operated in a multi-line mode. The sample was sequentially excited by these four and the corresponding thermal lens signals were monitored by a He-Ne laser. Compared with other existing thermal lens apparatus, this four-color spectrophotometer has advantages that include its ability to provide identification of the analyte (as the ratios of the signals at four different excitation wavelengths) and to analyze simultaneously four-component samples without the need for any prior sample preparation. With this apparatus and with the use of 6-mW excitation beams modulated at 1.02 Hz, the detection limit for four-component samples is estimated to be about 10^?9 M, which is similar to the detection limit obtained for a one-component sample using a single-wavelength system.     

Thermal conductivity measurements using the flash method

Thermal diffusivity is the speed with which heat propagates through a material. It has a multitude of direct applications, such as determining heat transfer through brake pads at the moment of contact, etc., but more often it is used to derive thermal conductivity from the fundamental relationship tying it with specific heat capacity and density. Using a new multi-sample configuration system, and testing a reference sample adjacent to the unknown, specific heat capacity can be obtained parallel with thermal diffusivity. Thus, a single test yields thermal diffusivity and thermal conductivity with prior knowledge of density. The method is fast and produces results with high accuracy and very good repeatability. The sample size, 12 to 30 mm diameter and 2 to 5 mm thickness, is easy to handle and is well suited for a broad range of materials, even for composites, often a problem for other methods. Typical data on two polymers, Pyrex glass and Pyroceram 9606 are presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Polymeric Schiff Bases. VII. Some Parameters in the Evaluation of the Thermal Stability of Poly(p-Xylylidene-p-phenylenediamine)

Thermogravimetric analyses of poly(p-xylylidene-p-phenylenediamine) in nitrogen, helium, and air yield stability values substantially identical to values obtained from tests in vacuo. The respective thermal stability values in nitrogen and in air are unchanged over a fourfold change in gas flow rates. Slightly lower values are found at heating rates of 5–15°C/min than at 30°C/min. Thermal stabilities are lower in oxygen than in air, but the values are still relatively high. Higher apparent thermal stability values are observed when a powder sample of 10 mg is evaluated as a single mass rather than as a fine powder. Calorimetric measurements indicate that Schiff base polymers which have been heated in nitrogen to 1000–1200°C have not been converted to graphite-type polymers. The Schiff base polymers are resistant to radiation; their stability is shown to be independent of dose rate and of the nature of the ionizing radiation.