House-of-security approach to measurement in analytical chemistry: quantification of human error using expert judgments

A new technique for quantification of human errors in chemical analysis using expert judgments is described. This technique is based on the house-of-security approach developed recently in the field of safety and security for prevention of terrorist and criminal attacks against an organization. The following relative quantification parameters (expressed in %) are proposed in the technique: (a) likelihood score of human error in a chemical analytical measurement/testing method, (b) severity score of human error for reliability of the test results, (c) importance score of a component of a laboratory quality system, and (d) effectiveness score of the quality system as a whole in preventing/blocking human error. As an example, 34 scenarios of human error in pH measurement of groundwater are discussed and quantified.     

Human being as a part of measuring system influencing measurement results

The role of human being as a part of a measuring system in a chemical analytical laboratory is discussed. It is argued that a measuring system in chemical analysis includes not only measuring instruments and other devices, reagents and supplies, but also a sampling inspector and/or analyst performing a number of important operations. Without this human contribution, a measurement cannot be carried out. Human errors, therefore, influence the measurement result, i.e., the measurand estimate and the associated uncertainty. Consequently, chemical analytical and metrological communities should devote more attention to the topic of human errors, in particular at the design and development of a chemical analytical/test method and measurement procedure. Also, mapping human errors ought to be included in the program of validation of the measurement procedure (method). Teaching specialists in analytical chemistry and students how to reduce human errors in a chemical analytical laboratory and how to take into account the error residual risk, is important. Human errors and their metrological implications are suggested for consideration in future editions of the relevant documents, such as the International Vocabulary of Metrology (VIM) and the Guide to the Expression of Uncertainty in Measurement (GUM).     

钢中氧化物夹杂分析的误差来源及结果的可靠性

本文综述了采用化学-电化学方法分析钢中氧化物夹杂的误差来源。基体元素的水解、钝化、共存相的干扰和包裹相等引起正偏差;化学溶损、沉淀处理等引入的负偏差;以及随机误差。相应地提出了提高分析精度的具体措施。对这种既无标样又无标准可循的分析其结果的可靠性不仅需根据钢中氧含量而定,还需根据夹杂物的总量与分量的吻合程度来判定,此外要结合钢的化学成份,冶炼工艺,脱氧制度来综合判断。     

The Compositional Aspects of Edible Flowers as an Emerging Horticultural Product

Edible flowers are becoming very popular, as consumers are seeking healthier and more attractive food products that can improve their diet aesthetics and diversify their dietary sources of micronutrients. The great variety of flowers that can be eaten is also associated with high variability in chemical composition, especially in bioactive compounds content that may significantly contribute to human health. The advanced analytical techniques allowed us to reveal the chemical composition of edible flowers and identify new compounds and effects that were not known until recently. Considering the numerous species of edible flowers, the present review aims to categorize the various species depending on their chemical composition and also to present the main groups of compounds that are usually present in the species that are most commonly used for culinary purposes. Moreover, special attention is given to those species that contain potentially toxic or poisonous compounds as their integration in human diets should be carefully considered. In conclusion, the present review provides useful information regarding the chemical composition and the main groups of chemical compounds that are present in the flowers of the most common species.     

Use of modifiers with metal atomizers in electrothermal AAS: a short review

The evolution of chemical modifiers for Mo and W atomizers is slowly progressing, based mainly on trial and error experimentation. Despite repeated use of some chemical compounds, such as thiourea for Mo atomizers, at this point there is no panacea similar to the Pd+Mg mixture used widely in graphite furnace atomic absorption spectrometry. Clearly, the chemical processes involved during atomization from a metal atomizer differ significantly from those occurring in a graphite tube, so successful graphite modifiers may not be readily adapted to metal atomizers. As a result, the analyst must begin anew with the evaluation of many potential modifiers in hopes of finally arriving at some universal solution. The purpose of this review, with 62 references, is to describe that journey to date, and to point out some promising paths that may lead to future success: such as the development of permanent chemical modifiers for W and Mo electrothermal atomizers.     

Some theoretical considerations in analytical chemistry : A simple method of calculating acid - base titration errors

The error in acid-basc titrations is analysed into a chemical error due to disparity between end- and equivalence points, a visual (or instrumental) discrimination error due to uncertainty in remembering or comparing colours, and an indicator error due to consumption of titrant by the indicator Simple expressions arc derived for the calculation of the chemical error, and these arc progressively refined ultimately to expressions which are rigorous and exact under all conditions.     

Probable physical mechanisms of the activation of oncogenes through carcinogens

A brief review is given of the three main known biochemical mechanisms of human oncogene activation. The underlying possible physical and chemical mechanisms (both short- and long-range) caused by chemical carcinogens are also briefly discussed. The probable role in carcinogenesis of conformational solitons generated after the release of carcinogens previously bound to nucleotide bases is pointed out. For such a soliton the Hamiltonian is written down and the solution of classical equations of motion is outlined.     

生命元素图谱与化学元素周期表

旨在用化学语言表面与生命有关的问题。讨论了微量元素与生物体作用的规律性,人体生命元素平衡谱的构成,人与环境间精细的动态的物质交换平衡以及“天人合一”的哲学思想,指出生命元素在元素周期表中昂首翘尾的“近似动物体形”分布潜示生命的存在,提出不仅要注重有机营养平衡,更要注重无机营养平衡的观点。     

Visual pH Sensors: From a Chemical Perspective to New Bioengineered Materials

Many human activities and cellular functions depend upon precise pH values, and pH monitoring is considered a fundamental task. Colorimetric and fluorescence sensors for pH measurements are chemical and biochemical tools able to sense protons and produce a visible signal. These pH sensors are gaining widespread attention as non-destructive tools, visible to the human eye, that are capable of a real-time and in-situ response. Optical “visual” sensors are expanding researchers’ interests in many chemical contexts and are routinely used for biological, environmental, and medical applications. In this review we provide an overview of trending colorimetric, fluorescent, or dual-mode responsive visual pH sensors. These sensors include molecular synthetic organic sensors, metal organic frameworks (MOF), engineered sensing nanomaterials, and bioengineered sensors. We review different typological chemical entities of visual pH sensors, three-dimensional structures, and signaling mechanisms for pH sensing and applications; developed in the past five years. The progression of this review from simple organic molecules to biological macromolecules seeks to benefit beginners and scientists embarking on a project of pH sensing development, who needs background information and a quick update on advances in the field. Lessons learned from these tools will aid pH determination projects and provide new ways of thinking for cell bioimaging or other cutting-edge in vivo applications.     

Data analyzer computer program for neutron activation analysis

In order to save time, manpower and minimize human error, a new computer program was designed, built and implemented using Visual Basic 6.0. The new program automatically reads and recognizes all the information in the “peak reports” from Gammaplus software, and is capable of automatically detecting the chemical isotopes within samples and calculating their concentrations and uncertainties. With minimum input from the user, the software has proven to be fast, reliable and user friendly.     

Extraction of soil organic phosphorus

Organic phosphorus is an important component of soil biogeochemical cycles, but must be extracted from soil prior to analysis. Here we critically review the extraction of soil organic phosphorus, including procedures for quantification, speciation, and assessment of biological availability. Quantitative extraction conventionally requires strong acids and bases, which inevitably alter chemical structure. However, a single-step procedure involving sodium hydroxide and EDTA (ethylenediaminetetraacetate) is suitable for most soils and facilitates subsequent speciation by nuclear magnetic resonance spectroscopy. Analysis of extracts by molybdate colorimetry is a potential source of error in all procedures, because organic phosphorus is overestimated in the presence of inorganic polyphosphates or complexes between inorganic phosphate and humic substances. Sequential extraction schemes fractionate organic phosphorus based on chemical solubility, but the link to potential bioavailability is misleading. Research should be directed urgently towards establishing extractable pools of soil organic phosphorus with ecological relevance.     

Error bounds on the SCISSORS approximation method

The SCISSORS method for approximating chemical similarities has shown excellent empirical performance on a number of real-world chemical data sets but lacks theoretically proven bounds on its worst-case error performance. This paper first proves reductions showing SCISSORS to be equivalent to two previous kernel methods: kernel principal components analysis and the rank-k Nystro?m approximation of a Gram matrix. These reductions allow the use of generalization bounds on these techniques to show that the expected error in SCISSORS approximations of molecular similarity kernels is bounded in expected pairwise inner product error, in matrix 2-norm and Frobenius norm for full kernel matrix approximations and in root-mean-square deviation for approximated matrices. Finally, we show that the actual performance of SCISSORS is significantly better than these worst-case bounds, indicating that chemical space is well-structured for chemical sampling algorithms.     

Self-interaction error in density functional theory: a mean-field correction for molecules and large systems

Corrections to the self-interaction error which is rooted in all standard exchange-correlation functionals in the density functional theory (DFT) have become the object of an increasing interest. After an introduction reminding the origin of the self-interaction error in the DFT formalism, and a brief review of the self-interaction free approximations, we present a simple, yet effective, self-consistent method to correct this error. The model is based on an average density self-interaction correction (ADSIC), where both exchange and Coulomb contributions are screened by a fraction of the electron density. The ansatz on which the method is built makes it particularly appealing, due to its simplicity and its favorable scaling with the size of the system. We have tested the ADSIC approach on one of the classical pathological problem for density functional theory: the direct estimation of the ionization potential from orbital eigenvalues. A large set of different chemical systems, ranging from simple atoms to large fullerenes, has been considered as test cases. Our results show that the ADSIC approach provides good numerical values for all the molecular systems, the agreement with the experimental values increasing, due to its average ansatz, with the size (conjugation) of the systems.     

The chemical biology of apoptosis. Exploring protein-protein interactions and the life and death of cells with small molecules

Apoptosis, a fundamental process for both human health and disease, is initiated and regulated by protein-protein interactions, notable examples of which are the interactions involving Bcl-2 and IAP protein families. This article discusses recent advances in the use of chemical approaches in discovering and studying small molecules targeted to proteins of the Bcl-2 and IAP families. These small molecules and their complexes with receptors provide the tools and model systems to probe the basic mechanism of molecule recognition underling the life and death of cells and develop novel strategies for therapeutic intervention of the dysregulated apoptotic process. The review of these studies highlights the opportunity and challenge in this emerging area of chemical and chemical biological research.     

Scaling correction approaches for reducing delocalization error in density functional approximations

Delocalization error associated with the presently used density functional approximations is one of the main sources of errors which plague density functional theory calculations. In this paper, we give a comprehensive review on scaling correction(SC) approaches developed recently for reducing the delocalization error. The global and local SC approaches impose the rigorous Perdew-Parr-Levy-Balduz condition that the total electronic energy should scale linearly between integer electron numbers, on systems involving global and local fractional electron distributions, respectively. After presenting the theoretical background and mathematical formulation of scaling corrections, we demonstrate that they lead to universal alleviation of delocalization error. This is exemplified by the substantial improvement for the prediction of a wide range of electronic properties, including Kohn-Sham frontier orbital energies and band gaps, dissociation behavior of molecules, reaction barriers, electric polarizabilities, and charge-transfer species. The encouraging performances of SC approaches highlight their practicality and usefulness, and also affirm that an explicit treatment of fractional electron distributions is essentially important for reducing the intrinsic delocalization error. The existing limitations, the remaining challenges, and the future perspectives of SC are also discussed. Moreover, the SC approaches are compared with some existing methods attempting to remove the self-interaction error, such as the Perdew-Zunger self-interaction correction, the local hybrid hyper-generalized gradient approximations, and the rangeseparated density functional approximations. The unique advantages of SC suggest that it could open a novel and potentially paradigm-changing route for advancing density functional theory methods towards chemical accuracy.     

Lycopene: The need for better methods for characterization and determination

The healthy properties of lycopene – a red pigment present in tomato and other vegetables and fruits – make it a key carotenoid in the human diet. The present demand of high-purity lycopene for use in food, pharmaceutical, cosmetic and dye industries makes it essential to revisit its chemical characteristics, human absorption, transport and distribution in tissues, metabolism and, particularly, the analytical methods available for its extraction, separation, detection and preparative isolation. The aim of this state-of-the-art review of lycopene is to establish a starting point for the new research needed on this topic.     

How the Chemical Properties of GBCAs Influence Their Safety Profiles In Vivo

The extracellular class of gadolinium-based contrast agents (GBCAs) is an essential tool for clinical diagnosis and disease management. In order to better understand the issues associated with GBCA administration and gadolinium retention and deposition in the human brain, the chemical properties of GBCAs such as relative thermodynamic and kinetic stabilities and their likelihood of forming gadolinium deposits in vivo will be reviewed. The chemical form of gadolinium causing the hyperintensity is an open question. On the basis of estimates of total gadolinium concentration present, it is highly unlikely that the intact chelate is causing the T₁ hyperintensities observed in the human brain. Although it is possible that there is a water-soluble form of gadolinium that has high relaxitvity present, our experience indicates that the insoluble gadolinium-based agents/salts could have high relaxivities on the surface of the solid due to higher water access. This review assesses the safety of GBCAs from a chemical point of view based on their thermodynamic and kinetic properties, discusses how these properties influence in vivo behavior, and highlights some clinical implications regarding the development of future imaging agents.