Genetic programming: a novel method for the quantitative analysis of pyrolysis mass spectral data

A technique for the analysis of multivariate data by genetic programming (GP) is described, with particular reference to the quantitative analysis of orange juice adulteration data collected by pyrolysis mass spectrometry (PyMS). The dimensionality of the input space was reduced by ranking variables according to product moment correlation or mutual information with the outputs. The GP technique as described gives predictive errors equivalent to, if not better than, more widespread methods such as partial least squares and artificial neural networks but additionally can provide a means for easing the interpretation of the correlation between input and output variables. The described application demonstrates that by using the GP method for analyzing PyMS data the adulteration of orange juice with 10% sucrose solution can be quantified reliably over a 0-20% range with an RMS error in the estimate of ～1%.     

Automated derivatization instrument: preparation of alditol acetates for analysis of bacterial carbohydrates using gas chromatography/mass spectrometry

An automated derivatization instrument was developed for preparation of alditol acetates for GC/MS profiling of bacterial carbohydrates. The multistage alditol acetate method is now performed sequentially by a computer-controlled instrument. A series of electrically driven solenoid valves are in-line with a 21-sample manifold. A set of solvent valves controls the input of solvent and/or nitrogen gas to each sample chamber. A set of gas valves controls output to atmosphere or vacuum. Additionally, closure of all valves allows the sample to be sealed in a closed chamber. Temperature is also determined automatically. The availability of this instrument could help popularize the alditol acetate procedure and serve as a prototype for automation of other complex derivatization procedures.     

In-line catalytic derivatization method for selective detection of chlorinated aromatics with a hyphenated gas chromatography/laser mass spectrometry technique: a concept for comprehensive detection of isomeric ensembles

The combination of gas chromatography (GC) and laser-based resonance-enhanced multiphoton ionization-time-of-flight mass spectrometry (REMPI-TOFMS) represents a three-dimensional analytical method, using the gas chromatographic retention time, the wavelength of the ionization laser for REMPI, and the molecular mass as analytical parameters. In this work, a novel analytical scheme for detection of chlorinated aromatic compounds, including isomeric ensembles, by GC/REMPI-TOFMS is presented. The concept uses an in-line hydrodechlorination catalyst for post- or precolumn derivatization of chlorinated aromatic compounds. The chlorinated aromatics are quantitatively reduced, forming their respective aromatic skeletons. These aromatic skeletons are detected selectively by REMPI-TOFMS. The first results for substance class selective detection of chlorinated benzene isomers are given, and potential applications in the field of the analysis of compounds such as polychlorinated dibenzo-p-dioxins and -furans are discussed.     

Theoretical study of high-performance frontal analysis: a chromatographic method for determination of drug-protein interaction

High-performance frontal analysis (HPFA), a chromatographic method to determine unbound drug concentration in drug-protein binding equilibrium, has been considered on the basis of a theoretical plate model, where a rapid equilibrium of drug-protein binding in the mobile phase in the interstices of packing materials and a chromatographic partition equilibrium of the drug were taken into account simultaneously. When a certain excess volume of drug-protein mixed solution is injected directly into a HPFA column packed with a restricted-access type phase that excludes protein but retains drug in the micropores, the drug is eluted as a zonal peak with a plateau region. The elution profile can be well simulated by the mass balance equation derived according to a relatively simple plate theory concept, which confirms that the drug concentration in the plateau range agrees with the unbound drug concentration in the sample solution. The model was applied to the theoretical and systematic investigation of the dependence of the HPFA profile on several chromatographic conditions and the properties of the sample solution, such as injection volume of sample solution, drug and protein concentrations in sample solution, capacity factor of the drug, theoretical plate number, and binding parameters. The smaller capacity factor and the higher column efficiency lead to the larger plateau volume. The lower drug concentration, the higher protein concentration, and the stronger binding constant, which give the lower unbound drug fraction, lead to the larger plateau volume and allow frontal analysis with a smaller sample size.     

Online comprehensive RPLC × RPLC with mass spectrometry detection for the analysis of proteome samples

LC-MS-based shotgun proteomics relies both on the power of the separation techniques and the sensitivity of detection methods. As a viable alternative to classical approaches in this field, we developed a fully automated, comprehensive 2D LC system, in which RPLC × RPLC was coupled to MS detection, for the first time, and applied for the analysis of tryptic digests obtained from α-casein and dephosphorylated α-casein. The use of a significantly different pH in the two dimensions allowed us to attain high peak capacity, despite the employment of novel identical stationary phases. Furthermore, such a combination addresses compatibility issues, thus allowing straightforward interfacing in online 2D LC configuration, as well as direct linkage to a mass spectrometer. A theoretical peak capacity of ca. 8500 was calculated for the setup, employing four serially coupled C18 columns in the first dimension (600 × 2.1 mm, 2.7 μm d.p.), operated under basic conditions, and 3 cm length of the same stationary phase (30 × 4.6 mm, 2.7 μm d.p. column), under acidic conditions, for fast second dimension analysis.     

Isotope dilution mass spectrometry — A primary method of measurement and its role for RM certification

This article describes the application of isotope dilution mass spectrometry (IDMS) to the field of reference material (RM) characterisation focusing on the approach, which is applied by the IDMS group at BAM. Emphasis is placed on IDMS measurements of highest analytical quality. Basic principles as well as the equation system are being recalled. Different calibration strategies, such as single, double or triple IDMS, are critically reviewed and the achievable uncertainties are discussed. Differences in the application of thermal ionization mass spectrometry (TIMS) and inductively coupled plasma mass spectrometry (ICPMS) are discussed as well as differences between different types of mass spectrometers such as single collector versus multi-collector or quadrupole versus magnetic sector instruments. Possible sources of errors and bias are mentioned and correction models introduced and applied within the past years are discussed. Several examples for RM characterisations in the field of elemental analysis are shown, each demonstrating excellent analytical quality. In general it can be stated that IDMS is the most important reference method for elemental analysis, offering highest accuracy and precision or smallest measurement uncertainties, when properly applied. Thus IDMS represents by far the best suited reference method for RM characterisation. Due to its universal applicability IDMS offers sufficient potential to follow future needs in analytical chemistry as well as in the RM sector     

Extremely deep profiling analysis of the atomic composition of thick (>100 μm) GaAs layers within power PIN diodes by secondary ion mass spectrometry

A new opportunity to analyze the atomic composition of thick (>100 μm) epitaxial GaAs layers by SIMS with lateral imaging of the cross section of a structure is demonstrated. The standard geometry of ldepth analysis turns out to be less informative owing to material redeposition from the walls of a crater to its floor occurring when the crater depth reaches several micrometers. The profiles of concentration of doping impurities Te and Zn and concentrations of Al and major impurities in PIN diode layers are determined down to a depth of 130 μm. The element sensitivity is at the level of 10¹⁶ at/cm³ (typical for depth analysis at a TOF.SIMS-5 setup), and the resolution is twice the diameter of the probing beam of Bi ions. The possibility of enhancing the depth resolution and the element sensitivity of the proposed analysis method is discussed.     

A new approach to the diagnostics of nanoislands in Ge x Si1 − x /Si heterostructures by secondary ion mass spectrometry

A new approach to the diagnostics of Ge _x Si_{1 ? x} /Si heterostructures with self-assembled nanoislands, which is based on the method of secondary ion mass spectrometry (SIMS) using secondary Ge₂ cluster ions, is discussed. Calibration dependences of the yield of atomic (Ge) and cluster (Ge₂) secondary ions on the concentration of germanium in homogeneous Ge _x Si_{1 ? x} have been obtained for a TOF.SIMS-5 setup. It is established that, in contrast to the well-known linear dependence of ⁷⁴Ge/³⁰Si ∫ x/(1 ? x), the secondary Ge₂ cluster ions obey the quadratic relation Ge₂/³⁰Si ∫ [x/(1 ? x)]². It is shown that the proposed SIMS depth profiling using nonlinear calibration relations for Ge₂ cluster ions provides expanded information on multilayer Ge _x Si_{1 ? x} /Si heterostructures with nanoislands. By using this approach, without additional a priori data on the sample structure, it is possible to distinguish planar layers and GeSi layers with three-dimensional nanoislands, estimate the height of islands, reveal the presence of a wetting layer, and trace the evolution of islands during their formation in a multilayer structure.     

Nuclear magnetic resonance imaging – a potential method for analysis of bone material

The basic usage of nuclear magnetic resonance (NMR) microimaging for materials characterization is introduced. An application of microimaging for three-dimensional structural study of trabecular bone is presented with elementary types of image presentation. Solid bone in itself does not produce any significant NMR intensity and natural lipids and/or added 70% ethanol has been used as a signal source. The applied pulse sequences were three-dimensional spin echo and three-dimensional chemical shift selective spin echo. © 1998 Chapman & Hall     

Visualization of deuterium flux and grain boundary diffusion in duplex stainless steel and Fe–30 % Ni alloy,using secondary ion mass spectrometry equipped with a Ga focused ion beam

Time of flight secondary ion mass spectrometry (TOF-SIMS) equipped with a high spatial resolution Ga focused ion beam (Ga-FIB) was applied to understand hydrogen diffusion and desorption behavior in duplex stainless steel and Fe–30 % Ni alloys. Deuterium was used as a tracer of hydrogen. Results showed that the secondary ion intensity from body-centered cubic (bcc) and face-centered cubic (fcc) Fe represents the flux of deuterium from the surface and the concentration of deuterium, respectively. The deuterium-depleted zone can be visualized from the interface between bcc and fcc phase to fcc Fe on the surface. Furthermore, direct visualization of the grain boundary diffusion of deuterium is also possible in fcc Fe–30 % Ni alloys, using Ga-FIB-TOF-SIMS.     

Perovskite‐type Li‐ion solid electrolytes: a review

All-solid-state lithium batteries with inorganic solid electrolytes are recognized as the next-generation battery systems due to their high safety and energy density. To realize the practical applications of all-solid-state lithium battery, it is essential to develop solid electrolytes which exhibit high Li-ion conductivity, low electron conductivity, wide electrochemical window, and low interface resistance between the electrode and the solid electrolyte. Among many solid electrolytes, the perovskite-type lithium-ion solid electrolytes are promising candidates that can be applied to all-solid-state lithium batteries. However, the perovskite-type solid electrolytes still suffer from several significant problems, such as poor stability against lithium metal, high interface resistance, etc. In this review, we have analyzed and summarized the properties of perovskite-type solid electrolytes with two different systems, namely three-component oxide system Li_3xLa_2/3?xTiO₃ (LLTO) and four-component oxide system (Li, Sr)(B, B’)O₃ (B?=?Zr, Hf, Ti, Sn, Ga, etc., B’ = Nb, Ta, etc.). LLTO and (Li, Sr)(B, Ta)O₃ compounds exhibit high Li-ion conductivity of up to >?10^??4 S·cm^??1 at room temperature. Based on the review of academic literature, the ion transportation mechanism, composition design, electrical properties, stability, doping, and application of these solid electrolytes are discussed, which would be helpful for the further development of all-solid-state lithium batteries.

     

Temperature-resolved molecular emission spectroscopy: an analytical technique for solid materials

Temperature-resolved molecular emission spectroscopy is described as a thermal analysis method for the analysis of solids and liquids. The technique uses an electrically heated graphite cup to decompose and/or vaporize the sample. The vapors are carried by a stream of argon into a cool hydrogen diffusion flame. Both the quantity and the nature of the decomposed species can be determined. The technique is particularly useful for the determination of sulfur, phosphorus, or nitrogen. Calibration curves for sulfur show the expected parabolic shape, and those for phosphorus are linear. The detection limit for elemental sulfur was determined to be approximately 50 ng. The evolution of sulfur is shown to be related to the decomposition temperature which is characteristic of the sulfur-containing species. Reproducibility of the decomposition temperatures is typically ±2%.     

Secondary ion mass spectrometry and multireflection infrared analyses of conversion coatings on Fe–Cr–Al stainless steels for catalysis: study of thermal stability

Abstract

The thermal stability of three stainless steel conversion coatings for high temperature applications (e.g. photothermal conversion catalysis) are investigated. The thermal oxidation in air up to 1000°C of Fe–17Cr, Fe–18Cr–1·3Al, and Fe–22Cr–5Al coatings (all wt-%) are compared. This study has revealed a critical temperature below which the coating thickness is preserved; the critical temperature increases and the thermal oxidation of the conversion coating decreases with higher chromium and aluminium content. This is attributed to the difference in the substitution ratio of γ lacunar phase (additionally oxidised substituted magnetite), which is the main component of the conversion coatings. The thermal stability of this phase is higher when it is richer in chromium or aluminium. Higher contents of these elements raise the temperature of formation of chromite (FeCr₂O₄) and alumina, the occurrence of which causes thickening of the coating during thermal treatment.

MST/1891     

Examination of the suitability of α-tocopherol as a stabilizer for ultra-high molecular weight polyethylene used for articulating surfaces in joint endoprostheses

The lifetime of articulating surfaces in joint endoprostheses made of ultra-high molecular weight polyethylene (UHMW-PE), especially of UHMW-PE-cups of hip-endoprostheses, is usually limited to 10–15 years due to material failure as a result of oxidation of the UHMW-PE in vivo. In this study the suitability of the natural antioxidant -tocopherol (vitamin E) as a stabilizer for UHMW-PE in these applications was investigated. Specimens with 0.1%, 0.2%, 0.4% and 0.8% w/w -tocopherol as well as unstabilized samples were sintered and sterilized with -rays at 25 kGy in accordance with standard processing methods of cups for total hip-endoprostheses. These specimens were aged in pure oxygen at 70 °C and 5 bar as well as in aqueous H₂O₂ at 50 °C. The degree of oxidation was observed by means of FTIR-spectroscopy, DSC analysis and mechanical testing. The FTIR-measurements showed that -tocopherol can prolong the lifetime of UHMW-PE in an oxidative environment by a factor of more than 2.5. In the mechanical tests no embrittlement could be observed with the stabilized samples. A comparison with the standard antioxidant system Irganox® 1010/Irgafos® 168 (Ciba-Geigy, Switzerland) was carried out and revealed that -tocopherol can even exceed the stabilization effect of this widely-used antioxidant system.     

Time-dependent oxidation during nano-assisted laser desorption ionization mass spectrometry: a useful tool for structure determination or a source of possible confusion?

This work reports on a new and extremely simple approach for determination of a double bond position by a laser desorption ionization mass spectrometry. It is solely based on the catalytic properties of nanostructured surfaces used in nanoassisted laser desorption ionization experiments. These surfaces can induce oxidation of analytes, which results in a mass shift that can be detected by mass spectrometry. If a site of unsaturation is oxidized and cleaved, the m/z difference is diagnostic of the position of a double bond. By demonstrating that the oxidation depends on the analyte surface dwell time, it was proven that it is caused by the surface activity and not by the laser desorption ionization process itself. Control matrix-assisted laser desorption/ionization (MALDI) experiment showed only a limited partial oxidation and no time dependency of the process. The ability to determine a position of a double bond was demonstrated on polyunsaturated phospholipids and cyclosporine A. In some other cases, however, the unexpected oxidation could cause confusion, as demonstrated for a glycosphingolipid from a porcine brain extract.     

Laser-induced liquid bead ion desorption mass spectrometry: an approach to precisely monitor the oligomerization of the β-amyloid peptide

In the present work, the recently developed laser-induced liquid bead ion desorption mass spectrometry (LILBID MS) is applied as a novel technique to study Aβ oligomerization, thought to be crucial in Alzheimer's disease (AD). The characterization of the earliest nucleation events of this peptide necessitates the application of several techniques to bridge the gap between small oligomers and large fibrils. We precisely monitored in time the transformation of monomeric Aβ (1-42) into oligomeric Aβ(n) (n < 20) and its dependence on concentration and agitation. The distribution shows signs of the hexamer being crucial in the assembly process. The intensity of the monomer decreases in time with a time constant of about 9 h. After a lag time of around 10 h, a phase transition occurred in which the total ion current of the oligomers goes to nearly zero. In this late stage of aggregation, protofibrils are formed and mass spectrometry is no longer sensitive. Here fluorescence correlation spectroscopy (FCS) and transmission electron microscopy (TEM) are complementary tools for detection and size characterization of these large species. We also utilized the oligomers of Aβ (1-42) as a model of the corresponding in vivo process to screen the efficacy and specificity of small molecule inhibitors of oligomerization. The LILBID results are in excellent agreement with condensed phase behavior determined in other studies. Our data identified LILBID MS as a powerful technique that will advance the understanding of peptide oligomerization in neurodegenerative diseases and represents a powerful tool for the identification of small oligomerization inhibitors.     

The ‘linguistic pattern’ method for a workstation layout analysis

The ‘Linguistic Pattern’ approach to the facilities and panels layout is presented. This approach is based on Zadeh's possibility theory and the Lukasiewicz multivalued implication formula. The idea of the approach is presented on the basis of a simple exemplary problem of an automobile display arrangement. The general idea of a computer algorithm is presented and some potential benefits of the proposed approach are discussed.     

Extrinsic problem of mass exchange for a solid sphere and a drop at high peclet numbers and Re ≤100

Based on the solution of the problem of flow around a liquid sphere for 0.5Re100, values are found for the mass-transfer coefficients for a solid sphere, a drop, and a gas bubble in diffusion boundary-layer approximation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 1, pp. 69–72, January, 1976.     

Application of pyrolysis–gas chromatography/mass spectrometry for the identification of polymeric materials in failure analysis in the automotive industry

The application of analytical pyrolysis–gas chromatography mass spectrometry (Py–GC/MS) in the failure analysis of two hydraulic cylinders and their rubber membranes from the automotive industry were presented.     

Layer-by-layer analysis of the chemical state of iron in carburized steel surfaces by conversion electron Mössbauer spectrometry

Conversion electron Mössbauer spectra revealed that the uppermost surface layer of a carburized and quenched steel was almost -austenite and that the surface layer of this sample consisted of -martensite and -austenite. Iron carbide was expected to have been formed in the surface layer of a carburized and annealed steel but, in fact, no iron carbide could be recognized in the sample. This may be due to the de-carburization or the re-diffusion of carbon into the steel. However, conclusive evidence supporting this explanation was not obtained.