New theoretical expressions for the five adsorption type isotherms classified by BET based on statistical physics treatment

New theoretical expressions to model the five adsorption isotherm types have been established. Using the grand canonical ensemble in statistical physics, we give an analytical expression to each of five physical adsorption isotherm types classified by Brunauer, Emett, and Teller, often called BET isotherms. The establishment of these expressions is based on statistical physics and theoretical considerations. This method allowed estimation of all the mathematical parameters in the models. The physicochemical parameters intervening in the adsorption process that the models present could be deduced directly from the experimental adsorption isotherms by numerical simulation. We determine the adequate model for each type of isotherm, which fixes by direct numerical simulation the monolayer, multilayer, or condensation character. New equations are discussed and results obtained are verified for experimental data from the literature. The new theoretical expressions that we have proposed, based on statistical physics treatment, are rather powerful to better understand and interpret the various five physical adsorption type isotherms at a microscopic level.     

Modeling and analytical simulation of rotating disk ultrafiltration module

An unsteady state mass transfer model has been developed for rotating disk ultrafiltration module. Starting from the basic physics of the system, analytical expression of back transport flux generated due to rotation-induced shear field is determined, which is subsequently incorporated in the fundamental material balance equation. In order to get an analytical solution of governing partial differential equation via Laplace transformation, pseudo steady state consideration is imposed both on permeate as well as back transport flux. Once the analytical form of concentration field is obtained using the expression permeate flux, membrane surface concentration are evaluated using polymer solution theory and irreversible thermodynamics. Finally an iterative scheme is designed to simulate the permeate flux and membrane surface concentration under specified set of operating parameters. The prediction from this model is found to be in good agreement with experimental data obtained from PEG-6000/water system using cellulose acetate membrane of 5000 Da molecular weight cut-off.     

Molecular springs, muscles, rheostats, and precessing gyroscopes: from review to preview

The concepts of molecular springs and gyroscopes have existed for some time, and there have been numerous reports published about these fascinating topics. Here we describe our interest in this topic, reviewing our initial progress. This is not a complete story, rather an offering of synthetic strategies, interesting molecular structures, observations, and possibilities. In many cases, the "properties" component of the structure-property relationship for a given compound is the result of a computational prediction. Given the present state of theoretical chemistry, a computer's predictive power can far exceed that which can be presently accomplished by existing experimental analytical means. The theoretical results reported here allude to intriguing possibilities. Hopefully, this intrigue will help catalyze the development of definitive, albeit rather esoteric, single-molecule analytical experiments. The intentionally speculative nature of this review is intended to stimulate new challenges for and perspectives from those in related fields of interest; hopefully presenting a preview of what is to come.     

Analytical Chemistry in the USSR

Abstract

In the USSR analytical chemistry is one of the most important of the chemical disciplines. Since its beginning as an independent part of the chemical research, analytical chemistry has developed as an integral part of the political economy, and serves the practical needs of industry, as well as being a theoretically well-founded science. Besides economically important problems like the analysis of the composition of sediments of raw materials, quality control in metallurgy and in the production of rare elements, analytical control in the chemical, pharmaceutical, nuclear-energy and semiconductor production are of importance, and furthermore, analysts develop their own theory, and success in many phases of development are related to a knowledge of other sciences, especially to physics, mathematics, general chemistry, metallurgy, biology, etc.     

Analytical optimization of some parameters of a Laser-Induced Breakdown Spectroscopy experiment

Laser-Induced Breakdown Spectroscopy (LIBS) experiments are performed on standard metallic samples, in air at atmospheric pressure, using a Nd:YAG laser at 1064 nm and a fiber located close to the plasma to collect its emission. This configuration is chosen because it is representative of many LIBS setups. The influence of several experimental parameters is studied in order to optimize the analytical performances: signal-to-background ratio (SBR), line intensity and repeatability. Temporal parameters of the detector are adjusted for each measurement to maximize the SBR. The signal is found to linearly depend on the pulse energy over our range of investigation. This behavior is related to the increase of the number of vaporized atoms when the pulse energy increases. Complementary measurements of plasma dimensions support our conclusions. We show the existence of an optimum fluence on the sample that gives the highest signal and the lowest relative standard deviation (RSD), and which does not depend on the pulse energy. Finally we demonstrate that ablation is much more efficient using a laser beam with a high numerical aperture, other experimental parameters being unchanged, because of a less pronounced laser shielding by the plasma. Analytical consequences of this result are discussed.     

Injection profiles in liquid chromatography. I. A fundamental investigation

This is a fundamental experimental and theoretical investigation on how the injection profile depends on important experimental parameters. The experiments revealed that the injection profile becomes more eroded with increased (i) flow rate, (ii) viscosity of the eluent, (iii) size of the solute, (iv) injection volume and (v) inner diameter of the injection loop capillary. These observations cannot be explained by a 1D-convection-diffusion equation, since it does not account for the effect of the parabolic flow and the radial diffusion on the elution profile. Therefore, the 1D model was expanded into a 2D-convection-diffusion equation with cylindrical coordinates, a model that showed a good agreement with the experimental injection profiles dependence on the experimental parameters. For a deeper understanding of the appearance of the injection profile the 2D model is excellent, but to account for injection profiles of various injection volumes and flow rates in preparative and process-chromatography using computer-optimizations, a more pragmatic approach must be developed. The result will give guidelines about how to reduce the extra-column variance caused by the injection profile. This is important both for preparative and analytical chromatography; in particular for modern analytical systems using short and narrow columns.     

Another scientific practice separating chemistry from physics: thought experiments

Thought experiments in the history of science display a striking asymmetry between chemistry and physics, namely that chemistry seems to lack well-known examples, whereas physics presents many famous examples. This asymmetry, I argue, is not independent data concerning the chemistry/physics distinction. The laws of chemistry such as the periodic table are incurably special, in that they make testable predictions only for a very restricted range of physical conditions in the universe which are necessarily conditioned by the contingences of chemical investigation. The argument depends on how ‚thought experiment’ is construed. Here, several recent accounts of thought experiments are surveyed to help formulate what I call ‚crucial’ thought experiments. These have a historical role in helping to judge between hypotheses in physics, but are not helpful in chemistry past or present.     

Atomic physics and atomic spectroscopy: mother and daughter?

In Part 1 the roots of analytical atomic emission (AES), absorption (AAS), fluorescence (AFS), optogalvanic (OG) and forward-scattering (FS) spectroscopy in atomic physics are exposed. The essential differences between FS and AAS or AFS are stressed. The links of plasma-source mass-spectrometry with atomic spectroscopy and with flame ionization research are also indicated. Part 2 deals with various aspects of the continual interrelation between atomic physics and atomic spectroscopy. The usage of AAS in atomic physics is exemplified by shock-tube experiments on the oxidation of Cr atoms and the curve-of-growth of the Cr resonance lines in argon. Examples of the usage of AFS in physical experiments are given that relate to the collisional mixing of Zeeman substates and the far-wing profiles of the collisionally broadened Na-D lines. Other aspects of this interrelation are discussed that relate to the sources of atomization and excitation, to the detection or measuring techniques, and to the research or development of analytical methods and sources. In Part 3 the revival of AES and the prospects of some laser-based atomic spectroscopies are summarized, whereas a further exploitation of anomalous dispersion in analytical atomic spectroscopy is suggested. General conclusions and exhortations are collated in Part 4.     

Analytical Chemistry — today''s definition and interpretation

Conclusion Analytical Chemistry is an applied, experimental field of natural science and is based not only on chemistry, but also on physics, biology, information theory and many fields of technology. The purpose of Analytical Chemistry is to provide information on the chemical composition of natural and synthetic objects and the changes in this composition over space and time. It is a typical multidisciplinary subject with many feedback links emphasizing teamwork in solution of problems.     

Teaching the integrated and modern perspectives of analytical chemistry

The present situation of analytical chemistry teaching within a chemistry curriculum is exemplified by the reformed chemistry curriculum in Germany. This approach is contrasted with teaching analytical chemistry within a novel curriculum in natural sciences termed 'applied science'. The latter curriculum ensures a superior education in chemistry, physics, biology, mathematics and information science, thus gaining an integrated perspective of analytical chemistry.     

Teaching the integrated and modern perspectives of analytical chemistry

The present situation of analytical chemistry teaching within a chemistry curriculum is exemplified by the reformed chemistry curriculum in Germany. This approach is contrasted with teaching analytical chemistry within a novel curriculum in natural sciences termed ‘applied science’. The latter curriculum ensures a superior education in chemistry, physics, biology, mathematics and information science, thus gaining an integrated perspective of analytical chemistry.     

Introducing Field Environmental–Analytical Chemistry in the Quantitative Analysis Laboratory

Advances in instrumentation and technology now provide the ability to perform many quantitative determinations in the field. Additionally, the potential for sample degradation and analyte decomposition make it necessary to determine certain analytes (e.g., dissolved oxygen) in the field when conducting environmental analyses. Unfortunately, field environmental—analytical chemistry is not a substantial portion of the analytical chemistry curriculum at many institutions. Students in lower-level analytical chemistry courses are often non-chemistry science majors, particularly at institutions with small chemistry departments. We report here on an experiment in which field environmental-analytical chemistry is introduced in the quantitative analysis laboratory. In the context of a water quality assessment of a local river, students determine temperature, pH, ORP, nitrate nitrogen, and ammonia nitrogen at several points in the river. The experimental objective is to determine the potential effects local agricultural practices and treated wastewater discharge may be having on the water composition. The pedagogical objective is to expose these students to the difficulties involved in making analytical determinations in unfamiliar and/or disruptive settings.     

The Kalman filter in analytical chemistry

During the past ten years, the means by which more information can be extracted from experimental data have become an important area of research in analytical chemistry. Digital filters have been demonstrated to have a number of applications to analytical problems. These techniques typically involve a least-squares fit of experimental data to some model of the process being filtered. One method for filtering experimental data is based on the Kalman filter, a recursive, linear digital filter first developed for use in navigation, but now used in many fields. This paper discusses the implementation of Kalman filters in analytical chemistry. The principles of state-space digital filtering are reviewed, and the development of state/space models is discussed. Discussion is focused on the discrete Kalman algorithms. Two examples are provided to demonstrate the operation of the discrete Kalman filtering algorithm. Similarities between Kalman filtering and weighted least-squares methods are considered, and the specific advantages and disadvantages of linear and nonlinear Kalman filtering approaches are evaluated. To illustrate the range of problems which benefit from use of the filter, a comprehensive literature survey of the application of Kalman filtering to chemical problems is provided.     

The Life of a Surface Bubble

Surface bubbles are present in many industrial processes and in nature, as well as in carbonated beverages. They have motivated many theoretical, numerical and experimental works. This paper presents the current knowledge on the physics of surface bubbles lifetime and shows the diversity of mechanisms at play that depend on the properties of the bath, the interfaces and the ambient air. In particular, we explore the role of drainage and evaporation on film thinning. We highlight the existence of two different scenarios depending on whether the cap film ruptures at large or small thickness compared to the thickness at which van der Waals interaction come in to play.     

Electrothermal atomization from metallic surfaces: Part 3. Some new developments in design and performance of a tungsten-tube atomizer

A new design of a work-head for a tungsten-tube atomizer as well as voltage- and temperature-feedback circuits added to the power supply of a Varian model CRA-63 atomizer are described. The importance of rapid, temperature-controlled heating of the atomizer is shown. The effect of heating rate (0.5–20 K ms^-1) on the analytical signal of many elements is investigated; experimental atomization and residence times and peak absorbance values are evaluated. The analytical performance of the tungsten-tube atomizer is tested for elements of different volatilities.     

Multivariate analysis of nutritional information of foodstuff of plant origin for the selection of representative matrices for the analysis of pesticide residues

Testing safety of foodstuffs of plant origin involves the analysis of hundreds of pesticide residues. This control is only cost-effective through the use of methods validated for the analysis of many thousands of analyte/matrix combinations. Several documents propose representative matrices of groups of matrices from which the validity of the analytical method can be extrapolated to the represented matrices after summarised experimental check of within group method performance homogeneity. Those groups are based on an evolved expert consensus based on the empirical knowledge on the current analytical procedures; they are not exhaustive, they are not objectively defined and they propose a large list of representative matrices which makes their application difficult. This work proposes grouping 240 matrices, based on the nutritional composition pattern equivalence of the analytical portion right after hydration and before solvent extraction, aiming at defining groups that observe method performance homogeneity. This grouping was based on the combined outcome of three multivariate tools, namely: Principal Component Analysis, Hierarchical Cluster Analysis and K-Mean Cluster Analysis. These tools allowed the selection of eight groups for which representative matrices with average characteristics and objective criteria to test inclusion of new matrices were established. The proposed matrices groups are homogeneous to nutritional data not considered in their definition but correlated with the studied multivariate nutritional pattern. The developed grouping that must be checked with experimental test before use was tested against small deviations in food composition and for the integration of new matrices.     

Metrology in chemistry – a public task

 The importance of analytical chemistry is increasing in many public fields, and the demand for reliable measurement results is growing accordingly. A measurement result will be reliable only if its uncertainty has been quantified. This can be achieved only by tracing the result back to a standard realizing the unit in which the measurement result is expressed. The National Metrology Institutes (NMIs) can contribute to the reliability of the measurement results by developing measuring methods, and by providing reference materials and standard measuring devices. In fields in which the comparability of measurement results is of particular importance, they establish traceability structures. Responding to the globalization of trade and industry the International Committee for Weights and Measures (CIPM) agreed on an arrangement on the mutual recognition of calibration certificates (CIPM MRA) issued by the NMIs. Received: 19 April 2000 / Accepted: 28 July 2000     

Experimental studies of the electronic structure of graphene

Graphene, the single layer of hexagonally coordinated carbon, is a two-dimensional material with many unusual properties; its physical realization a few years ago has caused a storm of activities in the solid state physics and materials science communities. The intriguing “massless Dirac Fermion” character of its charge carriers renders graphene a unique study object in condensed matter physics, and we discuss how surface-related techniques such as photoemission, STM and LEED play a prominent role in these investigations. We report on experimental studies of the growth and electronic structure of epitaxial single and few layer graphene on silicon carbide. The unusual band structure of single layer graphene and its evolution as layers are added towards bulk graphite is studied. In the special case of the bilayer, the opening of a gap by inducing an asymmetry through the influence of doping is examined. Finally, the influence of many body processes on the spectral function is discussed on the basis of high resolution photoemission data. The discussion of these aspects gives a comprehensive overview of the electronic structure of graphene as examined by experiment.