Aflatoxin analysis at the beginning of the twenty-first century

Aflatoxin mycotoxins were first described in the early 1960s as important fungal toxins, which contaminate many different human foods and animal feeds. Accurate and sensitive determination of these carcinogenic compounds immediately became an important requirement to meet food safety concerns and new official legislated regulations. For these reasons, analytical methods for aflatoxins continued to develop over the decades, reflecting advances in analytical chemistry. Currently, a wide range of methods are available to analytical scientists, ranging from newly described multi-toxin liquid chromatography tandem mass spectrometry to rapid methods based on immunological principles. These latter methods can provide quantitative outputs or a simple rapid determination of contamination level above or below a pre-determined cutoff value. The newest official methods as validated by Association of Official Analytical Chemists International or Comité Européen de Normalisation rely on immunoaffinity column clean-up of conventional extracts, followed by high-performance liquid chromatography separation of the analogues with detection based on natural fluorescence or the fluorescence generated by various derivatisation methods. In selecting from this range of available methods, the analytical chemist must decide on the requirements of the analysis such that the method chosen is ‘fit for purpose’.     

On the existence of primary methods of measurement

 There is much discussion in chemical metrology about the definition of primary methods of measurement, just as a couple of years ago there was debate about its predecessors, absolute methods and definitive methods. It is argued in this paper that the designation of certain methods as being primary only makes sense if there is an outstanding property identified that is common to all primary methods, and not present for all non-primary methods. The aim to identify primary methods should not blur our notion that it is the good practice of analytical chemistry that produces good results, not a particular method of analysis.     

Symplectic Methods for the Numerical Solution of the Radial Shrödinger Equation

In this paper new symplectic-schemes for the numerical solution of the radial Shrödinger equation are proposed. In particular, symplectic integrators for Hamiltonian systems have been developed. Based on this approach, second- and third-order methods are proposed. These methods are more accurate than the existing ones. We compare these methods not only with the existing symplectic methods, but also with a classical Runge–Kutta–Nyström method.     

Analytical Studies on the Role of Oxidants of the Olefinic Double Bond in the Determination of Flunarizine

Simple, sensitive, and selective spectrophotometric methods (M₁ and M₂) for the assay of flunarizine (FZ) through the olefinic double bond are proposed. Method M₁ is based on the reaction of potassium permanganate to the olefinic double bond in FZ and estimating the unreacted permanganate with Fast Green FCF (FG FCF). Method M₂ involves the treatment of the olefinic double bond in FZ with a Lemieux reagent (KMnO₄ and NaIO₄) and estimating the aldehyde formed with 3-methyl-2-benzothiazolinone hydrazone (MBTH). The color produced in both methods has maximum absorption at 620 nm. The Beer's law limits, precision, and accuracy of the methods are checked by the reference method. The methods are found to be suitable for the determination of flunarizine. The recoveries range from 99.18 to 101.13%.     

Precision of integral methods for the determination of the kinetic parameters

In this paper, a systematic analysis of the errors involved in the determination of the kinetic parameters (including the activation energy and frequency factor) from five integral methods has been carried out. The integral methods analyzed here are Coats-Redfern, Gorbachev, Wanjun-Yuwen-Hen-Zhiyong-Cunxin, Junmeng-Fusheng-Weiming-Fang, Junmeng-Fang and Junmeng-Fang-Weiming-Fusheng method. The results have shown that the precision of the kinetic parameters calculated by the different integral methods is dependent on u (E/RT), that is, on the activation energy and the average temperature of the process.     

A Family of Trigonometrically-Fitted Symmetric Methods for the Efficient Solution of the Schrödinger Equation and Related Problems

In this paper a family of trigonometrically-fitted symmetric ten-step methods for the efficient solution of the Schrödinger equation and related problems is presented. Construction and stability analysis of the new methods is described. Numerical results obtained for the resonance problem of the one-dimensional Schrödinger equation show the efficiency of the new methods when they are compared with known methods in the literature.     

Family of Twelve Steps Exponential Fitting Symmetric Multistep Methods for the Numerical Solution of the Schrödinger Equation

In the present paper we present a family of twelve steps symmetric multistep methods. The explicit part of new family of methods is applied to the scattering problems of the radial Schrödinger equation. This application shows the efficiency of the new family of methods.     

The degree of efficiency, the degree of reproducibility and the equivalence probability in statistical comparisons of analytical methods for the determination of tin in tin ores

Summary In most cases investigations concerning the reproducibility of different analytical methods for the determination of tin in tin ores consist only in comparisons of means, i.e. detection of systematic errors. The fact that the methods use different calibrating procedures, on the one hand, and that their accuracy varies, on the other hand, makes it necessary, to look for more sensitive criteria. For this purpose, the degree of efficiency regarding the determination of the true mean of a reference method, the degree of (mutual) reproducibility, and the equivalence probability are defined and their meaning is statistically interpreted. The degree of efficiency ɛ of any two methods is defined as the ratio of their mean square errors in determining the true mean of a reference method. This quantity can be described by the ratio of the upper bounds for the probabilities of an error by the two methods. The degree of reproducibility P* of different analytical methods we understand as minimal probability of comparable measuring results. The equivalence probability P_e is defined as a-posteriori probability of the hypothesis that the two distribution functions considered are identical. The criteria ɛ, P* and P_e seem to be more suitable for statistical comparisons as compared to known statistical standard procedures, such as the t-test criterion. The applicability of these quantities was checked by the example of 6 different methods for the determination of tin in tin ores. For this purpose, it was necessary to evaluate objectively the efficiency of sample division in order to get reproducible final samples for analysis using the hierarchical two-way classification of variance analysis. General knowledge concerning the analytical methods used could be completed.     

Comparison of three methods for the determination of the electrical conductivity of ion-exchange polymers

The development of ion-exchange membranes techniques using an electrical potential gradient incite often to define the electrical conductivity of this category of functional polymers. The investigation methods of this conductivity did not stop to vary, to such a point that some results can be contradictory. So we have determined this dynamic characteristic in comparing three recent methods. This has been done with three ion-exchange membranes often used in industrial applications: CM1 and CM2, made from sulfonated and crosslinked polystyrene, and Nafion^® 117 made from sulfonated uncrosslinked polytetrafluoroethylene. Measurements were achieved in sodium chloride solutions, at concentrations from 0.1 to 2 mol l⁻¹. The results show, whatever the polymer microstructure, non-negligible disparities between the three methods.     

Planar chromatography at the turn of the century.

An overview of the state-of-the-art of modern thin-layer chromatography (planar chromatography) is presented with emphasis on the complementary features of thin-layer and column liquid chromatographic separations. The reasons for selecting thin-layer chromatography for a particular analysis are identified by its attributes: a disposable stationary phase; simultaneous parallel separations; static detection free of time constraints; storage device for chromatographic information; all sample components are observed in the chromatogram. Future prospects for improved separation performance in TLC using zone refocusing, forced flow and electroosmotic flow methods are discussed as well as increasing zone capacity by using two-dimensional development and coupling to column chromatographic methods. Advances in coupling thin-layer chromatography with spectroscopic methods for structural elucidation are also considered. Finally, some predictions are made for how thin-layer chromatography will be practiced in the future.     

Photoinitiation and electroinitiation in the polymerization of 2-vinylnaphthalene

The zinc chloride-catalyzed polymerization of 2-vinylnaphthalene (VN) with both photoinitiation and electronitiation methods was examined. Good yields were obtained with both methods, the electroinitiated process being somewhat faster. The mechanism for polymerization initiation was investigated through a detailed comparison of the kinetics. Both initiation methods show a similar response to increasing input energy and to change in salt to monomer mole ratio. Both methods indicate formation of a ZnCl₂–(2-VN)₂ complex as intermediate with the formation of the species being rate-determining. These results, together with other similar investigations, are then used to deduce a mechanism that involves the formation of an electronically excited donor–acceptor complex. It is argued that in certain salt-stabilized, electron-delocalized, aromatic systems, such excitation is possible in electroinitiation.     

DSC study of the kinetic parameters of the metastable phases formation during non-isothermal annealing of an Al–Si–Mg alloy

Kinetics of β″ and β′ precipitations in an AlSiMg have been studied under non-isothermal conditions using differential scanning calorimetry (DSC) technique. The variation of the activation energy as a function of transformed fraction is determined using two isoconversional methods of Kissinger–Akahira–Sunose (KAS) and Friedman. The results obtained using the two methods show a change in the activation energy for both metastable phases precipitations as a function of transformed fraction. The results obtained from KAS method as compared with those obtained from Friedman method, show some major disagreements between the two methods. The growth exponent, determined by Ozawa method, decreases as a function of temperature for both phases.     

Usefulness of capability indices in the framework of analytical methods validation

Analytical methods capability evaluation can be a useful methodology to assess the fitness of purpose of these methods for their future routine application. However, care on how to compute the capability indices have to be made. Indeed, the commonly used formulas to compute capability indices such as Cpk, will highly overestimate the true capability of the methods. Especially during methods validation or transfer, there are only few experiments performed and, using in these situations the commonly applied capability indices to declare a method as valid or as transferable to a receiving laboratory will conduct to inadequate decisions.     

Speciation of Heavy Metals in Soils and Sediments. An Account of the Improvement and Harmonization of Extraction Techniques Undertaken Under the Auspices of the BCR of the Commission of the European Communities

Abstract

An account is presented of a series of investigations and collaborative studies, initiated by BCR, on current methods of metal speciation by extraction of soils and sediments with chemical reagents. It was established by extensive consultation with European experts that the diverse procedures used could be harmonized into agreed methods. These methods, including both single extractant and sequential extraction procedures were subjected to collaborative, interlaboratory trials and the results, presented briefly here, showed that it was both possible and desirable that reference soils and sediments, characterised by certified values for extractable contents, be prepared. As a consequence of these studies two soils have been prepared and will shortly be the subject of interlaboratory analysis with a view to certification of their EDTA and acetic acid extractable contents of some heavy metals. Following this workshop a feasibility study of the agreed sequential extraction procedure will, it is believed, shortly lead to certification of sediments for contents extractable by a defined sequential extraction procedure.     

Review of separation methods for the determination of ammonium/ammonia in natural water

Ammonium (NH₄⁺) and ammonia (NH₃) in aquatic ecosystems are of great interest to environmental scientists because they can be used to study the nitrogen cycle and as water quality indicators. Analytical separation methods developed in recent decades have been used widely to determine NH₄⁺ and NH₃ in aqueous solutions. This review presents an overview of state-of-the-art separation methods and analytical techniques for determining NH₃/NH₄⁺ in natural water, including chromatographic methods, electrophoretic methods, extraction methods, membrane-based gas diffusion methods, membraneless gas diffusion methods, passive sampling methods, and paper-based analytical methods. Common detection techniques that can be used in conjunction with particular separation methods are described, phase-transfer strategies (liquid-liquid, liquid-solid, liquid-membrane-liquid, and liquid-gas-liquid methods) are highlighted, and the strengths and weaknesses of the separation methods are discussed. The outlook, challenges, and expected future developments in the field of separation methods for determining NH₄⁺ and NH₃ in natural water are presented.     

Some new aspects of the theory of radioanalytical methods based on the partial solvent extraction separation of the element to be determined

Interrelationship between the error of the radioanalytical methods and the concentration of the element to be determined has been found for extraction systems with different parameters K_ex, pH, a concentration of the extractant. Based on a mathematical discussion of this interrelationship, the criterion of the estimation of sensitivity has been proposed for the different radioanalytical methods based on the substoichiometric principle as well as some deviations from it.     

Analytical Methods for the Determination of 90Sr and 239,240Pu in Environmental Samples

Artificial long-lived radionuclides such as ⁹⁰Sr and ^239,240Pu have been long released into the environment by human nuclear activities, which have a profound impact on the ecological environment. It is of great significance to monitor the concentration of these radionuclides for environmental safety. This paper summarizes and critically discusses the separation and measurement methods for ultra-trace determination of ⁹⁰Sr, ²³⁹Pu, and ²⁴⁰Pu in the environment. After selecting the measurement method, it is necessary to consider the decontamination of the interference from matrix elements and the key elements, and this involves the choice of the separation method. Measurement methods include both radiometric methods and non-radiometric methods. Radiometric methods, including alpha spectroscopy, liquid scintillation spectrometry, etc., are commonly used methods for measuring ^239+240Pu and ⁹⁰Sr. Mass spectrometry, as the representative of non-radiometric measurement methods, has been regarded as the most promising analytical method due to its high absolute sensitivity, low detection limit, and relatively short sample-analysis time. Through the comparison of various measurement methods, the future development trend of radionuclide measurement is prospected in this review. The fully automatic and rapid analysis method is a highlight. The new mass spectrometer with ultra-high sensitivity shows strong analytical capabilities for extremely low concentrations of ⁹⁰Sr, ²³⁹Pu, and ²⁴⁰Pu, and it is expected to develop determination methods with higher sensitivity and lower detection limit.     

Applications of nuclear methods in the automotive industry

Over the years nuclear methods have proved to be a valuable asset to industry in general and to the automotive industry in particular. This paper summarizes some of the most important recent contributions of nuclear technology to the development of vehicles having high quality and long-term durability. Radiotracer methods are used to measure engine oil consumption and the wear rates of inaccessible components. Radiographic and tomographic methods are used to image fluids and structures in engines and accessory components. Tracers are used to understand combustion chemistry and quantify fluid flow. Gauging methods are used for inspection and process control. Nuclear analytical methods are used routinely for materials characterization and problem solving. Although nuclear methods are usually considered as the means of last resort, they can often be applied more easily and quickly than conventional methods when those in industrial engineering and R&D are aware of their unique capabilities.