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The amount of substance evaporated from the surface of a viscous dielectric liquid during nanosecond barrier discharge has been measured for the first time using a method based on the creation of a gas microbubble in the volume of liquid and subsequent generation of discharge in the bubble. By measuring increase in the bubble radius during discharge, it is possible to determine the amount of substance evaporated from the microbubble walls. It is established that millijoule energy deposition in discharge leads to the evaporation of several nanomoles of substance, and this amount grows with the deposited electric energy.

Following the revision of the International System of Units (SI), that takes effect on 20 May 2019, the unit mole is defined by using a fixed number of elementary entities. This number is the fixed numerical value of the Avogadro constant, which is the defining constant of the unit mole. This definition was made possible because the determination of the Avogadro constant had reached a level of relative uncertainty that allowed its value to be fixed and, at the same time, safeguard continuity of measurement results before and after the definition. The motivation for the revision of the SI and the mole in particular will be explained and the experimental work that allowed it is summarized.

A study is reported of the quantification of the amount of matter by secondary ion mass spectrometry (SIMS) when depth profiling a nominally 3.1 nm thick delta layer of FMOC-l-pentafluorophenylalanine in Irganox 1010. The depth profiles are made using 5 keV Ar2300+ cluster ions with analysis by 25 keV Bi3+ ions. Data for 89 negative secondary ions shows profiles whose integrated intensities as a function of depth, even when normalized to the intensity for the pure material, still vary over a factor of 12. This variation mainly arises from matrix effects that are measured here using separate samples with mixed layers of three intermediate compositions of the two materials. Matrix enhancements or suppressions vary widely from secondary ion to secondary ion and are not related to the energy of the analyzing Bi3+ ion. Strong effects can cause the delta layer signal to show structure that may be misinterpreted. The compositional profile is established by using trial Dowsett profiles, representing the compositi...

The base quantity ‘amount of substance’ is poorly understood and the name and symbol usually avoided. This is because of its formal interpretation as the number of entities multiplied by the reciprocal of the mysterious Avogadro constant, N A. If X signifies the kind of entities involved, the number of entities in a sample, N(X), is easily comprehended, and if m av(X) is the sample-average entity mass, the total mass, m(X) = N(X)m av(X)—an aggregate of N(X) average entity masses—is also conceptually straightforward. However, the corresponding amount of substance, n(X) = N(X)(1/N A)—an aggregate of N(X) ‘reciprocal Avogadro constants’—is incomprehensible unless some physical meaning can be attached to 1/N A. By contrast, the base unit, mole, is thought of by chemists as an aggregate of a particular number of entities: mol = $$ {\mathcal N}_{\rm{Avo}} $$ ent, where $$ {\mathcal N}_{\rm{Avo}} $$ is the Avogadro number (equal to g/Da) and ent represents one entity. It makes sense, therefore, to interpret amount of substance as an aggregate of a general number of entities: n(X) = N(X) ent—an easily grasped concept. A ‘reciprocal Avogadro constant’ is thus seen to actually be exactly one entity. One mole then corresponds to setting N(X) = $$ {\mathcal N}_{\rm{Avo}} $$ , for which the total mass is the relative entity mass in grams—conforming to the original mole concept.

The original version of this article unfortunately contained an error. The author would like to correct the error with this erratum. In the third sentence of the fifth paragraph, the symbol N was erroneously included. The correct version of this sentence should read

The International System of Units (SI) is founded on 7 SI base units (meter, kilogram, second, ampere, kelvin, mole, candela) for 7 base quantities (length, mass, time, electric current, thermodynamic temperature, amount of substance, luminous intensity) assumed to be mutually independent. There is a need for a new quantity that describes the quality or type of the substance. The processing and introduction of this quantity is investigated. The method of the maximum possible atomic number of elements in Mendeleev’s Periodic Table was used. Here is a proposal of the 8th base quantity called type of substance and its unit boscovich, B. This quantity cannot be derived from 7 existing quantities and therefore should be introduced as a separate new one. It is also explained why the unit boscovich for type of substance is suggested.

The debate about whether measurement reactivity exists in daily diary research on substance use is still unsettled due to the issues of study design and statistical methodology. This study proposes a time-varying effect model (TVEM) that characterizes the trajectory of substance use behaviors with nonparametric functions determined by the data rather than imposes presumed parametric functions. It also allows researchers to investigate the effect of measurement reactivity on not only the likelihood of using substances but also the amount of substance use. The TVEM was applied to analyze diary data on alcohol and marijuana use collected from an experiment, which randomized 307 participants in Michigan into daily and weekly assessment schedules during 2014–2016. This study found short-term measurement reactivity on alcohol use, but did not find a significant reactivity effect on marijuana use. The daily group had smaller odds of abstinence from drinking but lower expected drinking quantity in the first week of assessment, which dissipated by the second week. The results indicate that although daily self-monitoring could have short-term reactivity on substance use behaviors that tend to fluctuate across days, such as alcohol use, it does not affect substance use behaviors that are quite consistent, such as marijuana use. Our findings imply that although daily monitoring of drinking may motivate people to reduce the quantity consumed once they start to drink, it may also arouse their desire to start drinking. Yet, both effects tend to last only one week, as participants accommodate to the monitoring by the second week.

We study the motion of a substance in a channel that is part of a network. The channel has 3 arms and consists of nodes of the network and edges that connect the nodes and form ways for motion of the substance. Stationary regime of the flow of the substance in the channel is discussed and statistical distributions for the amount of substance in the nodes of the channel are obtained. These distributions for each of the three arms of the channel contain as particular case famous long-tail distributions such as Waring distribution, Yule-Simon distribution and Zipf distribution. The obtained results are discussed from the point of view of technological applications of the model (e.g., the motion of the substance is considered to happen in a complex technological system and the obtained analytical relationships for the distribution of the substance in the nodes of the channel represents the distribution of the substance in the corresponding cells of the technological chains). A possible application of the obtained results for description of human migration in migration channels is discussed too.

FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais O ensino de Química é permeado por conteúdos aos quais muitos estudantes apresentam dificuldades de compreensão. Sob essa premissa, o presente estudo busca investigar um dos temas que ainda carecem de atenção no processo de ensino e aprendizagem de Química: a grandeza Quantidade de Matéria e a sua unidade de medida, o mol. Para tanto, nos propusemos a fazer uma reconstrução histórica sobre o assunto, buscando abordar os conceitos atômicos presentes em John Dalton e o acirrado debate que acaba por arquitetar o conceito da constante de Avogadro, várias décadas depois. Para o desenvolvimento desse assunto no contexto da sala de aula, delimitamos alguns episódios históricos e seus partícipes, iniciando com a definição de átomo por Dalton, e encerrando com a definição da constante de Avogadro por Jean Perrin em 1909. Concomitantemente, procuramos investigar quais os principais fatores, para além dos científicos, que influenciaram na construção do conceito de Quantidade de Matéria. Tivemos também, o apoio de professores das universidades de Minas Gerais, que ao responderem um questionário, nos possibilitou conhecer quais as principais dificuldades conceituais de estudantes em fase inicial de graduação; e, também, as estratégias utilizadas pelos docentes para superar tais obstáculos. Realizamos, ainda, uma análise do ponto de vista histórico nos livros didáticos indicados pelo Plano Nacional do Livro Didático, dos anos de 2015 e de 2018, a fim de avaliarmos como essas obras tratavam o tema; e, consequentemente, termos um panorama, mesmo que parcial, do tipo de informação que os estudantes têm sobre Quantidade de Matéria, ao ingressarem na Universidade. Como última etapa da pesquisa, propusemos e aplicamos uma estratégia didática com Licenciandos em Química da Universidade Federal de Juiz de Fora. Para essa etapa, realizamos a intervenção em duas turmas, uma em fase inicial de curso, e a outra em fase de conclusão. Nossa estratégia didática buscou valorizar a História da Ciência de forma que os licenciandos pudessem ressignificar o conceito de Quantidade de Matéria. Acreditamos que esse possa ser um excelente recurso didático no Ensino de Química, pois a partir da contextualização histórica é possível que o estudante ressignifique conceitos, minimizando, assim, a atividade corriqueira de memorização. Mediante as diferentes intervenções didáticas utilizadas com os alunos iniciantes e concluintes, foi possível averiguar o aproveitamento didático advindo da estratégia de ensino proposta neste estudo. The teaching of chemistry is permeated by content and many students have difficulties understanding them. This research aims to investigate one of the topics that need to be studied in the teaching and learning process of Chemistry: the Amount of Substance and its unit of measure, the mol. To do so, we did a historical reconstruction on the subject and approach the atomic concepts of John Dalton and the debate on the theme that defined decades after this the concept of the Avogadro. For the development of this subject in the context of the classroom, we delimit some historical episodes and their participants, beginning with the definition of atom by Dalton, and ending with the definition of the constant of Avogadro by Jean Perrin in 1909. At the same time, we seek to investigate the main causes besides the scientists factors that influenced the construction of the by Amount of substance concept. We have had the support of professors from the universities of Minas Gerais who, when they answered the questionnaire, enabled us to know the main conceptual difficulties of students in the initial stage of graduation; and also the strategies used by teachers to overcome such obstacles. We also carried out an analysis from the historical point of view in the didactic books indicated by the National Plan of the Didactic Book, from the years of 2015 and 2018, in order to evaluate how these works dealt with the theme; and, consequently, we have a panorama, even if partial, of the type of information that the students have about Quantity of Matter upon entering the University. As a last step of the research, we proposed and applied a didactic strategy with Licentiates in Chemistry of the Federal University of Juiz de Fora. For this stage, we performed the intervention in two classes, one in the initial phase of the course, and the other in the completion phase. Our didactic strategy sought to value the History of Science so that the licenciandos could resignify the concept of Quantity of Matter. We believe that this can be an excellent didactic resource in the Teaching of Chemistry, because from the historical contextualization it is possible for the student to re-significate concepts, thus minimizing the routine activity of memorization. Through the different didactic interventions used with beginning and finishing students, it was possible to ascertain the didactic utilization coming from the teaching strategy proposed in this study.

This paper describes the results achieved by high school seniors on an item which involves translation of the equationP=kTinto a corresponding pictorial external representation. The majority of students (the classes of 2011, 2012 and 2013) did not give the correct answer to the multiple choice part of the translation item. They chose pictorial representations of the other gas laws (P=k/V, orV=kT) instead. Failure to choose the correct answer was surprising considering that the symbol for volume was absent which should have been the key clue. Through the analysis of students' explanations (the classes of 2011 and 2012) and interviews (the class of 2013) we considered the reasoning applied by students who chose the correct answer or distractors for the multiple choice part of the item. Among the students who answered correctly there were explanations which contained misconceptions. Several factors that lead to the unsuccessful translation between external representations have been discovered. Students interpreted the change in one quantity based on the notation for the change in another one because of deep rooted cognitive schemas about changing two quantities (volume and pressure, pressure and temperature, temperature and volume), without consideration that for such changes to be valid for gases all three quantities need to be considered for a certain amount of substance. Those cognitive schemas interfered with mathematical reasoning,i.e.students possessed limited understanding of the equations.

The amount of substance and its unit the mole is a basic concept in chemistry. However, previous research has shown that teaching and learning the concept are challenging tasks for both teachers and students. The purpose of this study was to pinpoint the problems which emerge in the teaching and learning process, and provide integrated suggestions for classroom instruction. By means of videotaping and interviews, the case studies explored how the mole is presented and conceptualized in two secondary classrooms in two different countries, Australia and Taiwan. Data analysis was based on a concept map and focused on how two key ideas were presented in the lessons and perceived by the students: (1) the definition of the mole, and (2) the concept of molar mass. The findings show that during the lessons on the mole, most of the time was spent on solving stoichiometric problems. Conceptually, the number aspect of the mole, that is, Avogadro's number, was emphasized; the concept of molar mass was introduced without meaningfully connecting it to the concept of relative atomic/molecular mass. Although the students were able to solve relevant problems, they could not coherently explain the relations among the concepts. Two critical components for a conceptual understanding of the mole emerged: (1) the number aspect of the mole needs to be justified by its mass aspect, and (2) the connection between molar mass and relative atomic/molecular mass needs to be explicitly explained. The two components provide one explanation for students' algorithmic learning and their confusion in learning about the mole, and serve as concrete suggestions for improving classroom instruction. The study once again manifested the significance of teaching for conceptual understanding in science education. It also exemplifies how a concept map of a specific scientific concept can also be a useful analytical tool in educational research. © 2015 Wiley Periodicals, Inc. J Res Sci Teach 53: 181–214, 2016.

The definition of the mole in the current SI and the draft definition for the “new SI” are reviewed. Current textbook treatments of the mole are compared to these official definitions. For historical perspective, the treatment of the mole and amount of substance in textbooks before and after those quantities were introduced into the SI in 1971 is reviewed. Textbook definitions have not always matched the official definitions, but they reflect the common usage of chemists. Textbook definitions will likely resemble the official definition more closely if the new SI is adopted, because the draft definition is closer than the current official definition to what is found in many textbooks. The SI base quantity amount of substance, however, will likely continue to pose problems for chemistry educators and to be widely ignored by practitioners of chemistry if it is retained. Official definitions and expert usage of some terms related to the mole (particularly amount of substance) do not always coincide.

Free acidity of aqueous solutions was initially defined in 1909 by Søren Peter Lauritz Sørensen as pH = −lgcH+ (c/mol·dm−3 or m/mol·kg−1 of the free hydrogen ions in solution, H+) soon (1910) was changed to pH = paH+ = −lgaH+, integrating the new concepts of activity, ai and activity coefficient γi, for the ionic species i under concern, H+ in this case; it is ai = −lg(miγi). Since individual ions do not exist alone in solution, primary pH values cannot be assigned solely by experimental measurements, requiring extra thermodynamic model assumptions for the activity coefficient, γH+, which has put pH in a unique situation of not being fully traceable to the International System of Units (SI). Also the concept of activity is often not felt to be as perceptible as that of concentration which may present difficulties, namely with the interpretation of data. pH measurements on unknown samples rely on calibration of the measuring setup with adequate reference pH buffers. In this work, the assignment of pH values to buffers closely matching the samples, e.g., seawater, is revisited. An approach is presented to assess the quantity pmH+ = −lgmH+ profiting from the fact that, contrary to single ion activity coefficients, mean activity coefficients, can be assessed based on experimentally assessed quantities alone, γExp ±, thus ensuring traceability to the mole, the SI base unit for amount of substance. Compatibility between γExp ± and mean activity coefficient calculated by means of Pitzer model equations, γPtz ±, validates the model for its intended use.

In their paper, Mohr and Phillips demonstrate that the SI's representation of 'plane angle' as dimensionless rather than as an independent dimensional quantity continues to create confusion. The authors also address perceived problems in terminology regarding numbers of items, such as discrete events or particles. However, their general philosophy of equating the dimensionless 'number of items' to '(number of items) × (item name)' leads to false conclusions, such as that the hertz is equal to 2π radians per second, and therefore not a coherent SI unit. In attempting to specify kinds of entities, the authors introduce descriptive labels into their supposed 'units,' resulting in confusion between number of entities and amount of substance. And, in discussing the mole and related fundamental constants, they incorrectly portray the Avogadro constant as a conversion factor, identically equal to 1, thereby corrupting the relationships between the Boltzmann constant and the universal gas constant, and between the elementary charge and the Faraday constant. In my comment, I explain and correct these and related errors.

In chemistry and in acid-base physiology, the Henderson-Hasselbalch equation plays a pivotal role in studying the behaviour of the buffer solutions. However, it seems that the general function to calculate the valence of acids, bases and ampholytes, N = f(pH), at any pH, has only been provided by Kildeberg. This equation can be applied to strong acids and bases, pluriprotic weak acids, bases and ampholytes, with an arbitrary number of acid strength constants, pKA, including water. By differentiating this function with respect to pH, we obtain the general equation for the buffer value. In addition, by integrating the titration curve, TA, proposed by Kildeberg, and calculating its Legendre transform, we obtain the Gibbs free energy of pH (or pOH)-dependent titratable acid. Starting from the law of electroneutrality and applying suitable simplifications, it is possible to calculate the pH of the buffer solutions by numerical methods, available in software packages such as Excel. The concept of buffer capacity has also been clarified by Urbansky, but, at variance with our approach, not in an organic manner. In fact, for each set of monobasic, dibasic, tribasic acids, etc., various equations are presented which independently fit each individual acid-base category. Consequently, with the increase in acid groups (pKA), the equations become more and more difficult, both in practice and in theory. Some examples are proposed to highlight the boundary that exists between acid-base physiology and the thermodynamic concepts of energy, chemical potential, amount of substance and acid resistance.

Quantitative analysis is an important field in the quality control of medicinal plants, aiming to determine the amount of pharmacologically active constituents in complex matrices. Often biological effects of herbal drugs are not restricted to single compounds, but are rather caused by a number of often biogenetically related plant metabolites. Depending on the complexity of the analyzed plant extract, conflicts between accuracy, such as total content assays using photometric or colorimetric methods, and comprehensiveness, e.g. quantification of one or a few lead compounds can occur. In this study, we present a qHNMR approach determining the total amount of cycloartanoids in black cohosh (Actaea racemosa) rhizomes. Perdeuterated methanol containing 1,2,4,5-tetrachloro-3-nitrobenzene as an internal standard was used for extraction. Amounts of cycloartanoids were then measured by integrating 1H NMR signals of all cycloartenoids' H-19 exo protons. Due to their unusually low chemical shifts, these signals are well separated from all remaining signals in crude extracts. Thus, accurate (recovery rates of 99.5-102.5%) and precise (relative standard deviations below 2.5%) quantification of cycloartanoids was accomplished. To the best of our knowledge, this is the first example of a quantification of the total amount of a pharmacologically relevant compound class by integration of one 1H NMR signal characteristic for all members of this particular compound class. Additionally, we propose a new term and unit for the evaluation of medicinal plants and herbal medicinal products: the "specific partial amount of substance" of pharmacologically active constituents, indicated in mmol/g.

The core objective of a chemical composition measurement is to determine its true value. However, when measuring the composition of a macroscopic sample with a large number of atoms or molecules, realizing the true value of the measurand at both the macroscopic and microscopic levels remains an unsolved theoretical problem. We find that the true value of a sample composition exists in any subsample of a homogeneous molecular population of the sample. Here, we propose the Central Law of Measurement of the Amount of Substance: “The homogeneity of a sample molecular population represents the measurement accuracy of the sample composition in an analytical procedure”. The Central Law is based on a homogeneous molecular population axiom in which the molecular composition of a sample is identical for any homogeneous subsample. Furthermore, we point out that, at the microscopic scale, Avogadro’s law does not hold true.

Understanding Concepts for Calculations: Amount of Substance and Mole

Just as the gram is an Avogadro number of daltons, g = (g/Da) Da, the current definition of the mole can be interpreted as an Avogadro number of entities, as it is often thought of by chemists—and it should be explicitly redefined this way. By introducing a hitherto missing atomic-scale unit for the amount of any substance, the entity (symbol ent), analogous to the dalton for mass, we can then define the mole as: mol = (g/Da) ent—i.e., an Avogadro number of entities. It is argued that the name for the base quantity should be “chemical amount,” by analogy with “electric current.” Recent proposals and counterproposals for redefining the mole (and renaming “amount of substance”) are critically discussed in light of the above intuitively obvious definition.

Within the Working Group on Inorganic Analysis (IAWG) of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM) international key comparisons and pilot studies related to inorganic analysis are carried to ensure consistency in this field at the highest level. Some of these comparisons deal directly with the preparation and characterization of monoelemental solutions or with topics, closely related. The importance of monoelemental solutions lies in the fact that almost every measurement in inorganic analysis relies on the comparison with either a reference material, or references in form of solutions, usually (mono)elemental solutions. All quantitative measurement approaches, e.g. isotope dilution or standard addition, need an accurate reference solution made from a well characterized reference material, prepared under full gravimetric control. These primary (monoelemental) solutions do not only serve as arbitrary references/calibration solutions, but they also link up measurement results to the International System of units (SI), this way establishing the so-called metrological traceability to a measurement unit of the SI. Without such solutions on the highest possible level of accuracy and with the smallest possible associated uncertainties (for e.g. element content and/or impurities), an analysis itself can never be as good as it could be with appropriate reference solutions. This article highlights select key comparisons and pilot studies dealing with monoelemental solution-related topics within the IAWG from the foundation of CCQM—25 years ago—up to latest achievements in the field of inorganic analysis.

Since several years, the seven base units, m (metre), kg (kilogram), s (second), A (ampere), K (kelvin), mol (mole), and cd (candela) of the SI, are under revision and re-definitions are being proposed by the CCU (the Consultative Committee on Units to the CIPM, the International Committee on Weights and Measures) [1]. The mechanism of such a re-definition is lengthy and not that well known, certainly not in the chemical measurement community. In essence, CCU prepares proposals to the CIPM that passes a final recommendation for decision to the CGPM (the General Conference on Weights and Measures). CGPM is convened every 4 years: 2003, 2007, 2011, then exceptionally after 3 years in 2014, then, presumably, in 2018. It decides in virtue of the powers given to it by the Diplomatic Treaty on the Metre, ‘Convention du Metre’, signed in 1875. To that effect, CCU informs (and collects opinions of) other Consultative Committees to the CIPM on units in various fields such as: Electricity and Magnetism (CCEM), Photometry and Radiometry (CCPR), Thermometry (CCT), Length (CCL), Time and Frequency (CCTF), Ionising Radiation (CCRI), Units (CCU), Mass and Related Quantities (CCM), Amount of Substance: metrology in chemistry (CCQM), Acoustics, Ultrasound, and Vibration (CCAUV).

The Avogadro constant, the number of entities in the amount of substance of one mole, links the atomic and the macroscopic properties of matter. Since the molar Planck constant is very well known via the measurement of the Rydberg constant, the Avogadro constant is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a new definition of the kilogram in terms of a fundamental constant. Here, we describe a new and unique approach for the determination of the Avogadro constant by “counting” the atoms in 1 kg single-crystal spheres, which are highly enriched with the 28Si isotope. This approach has enabled us to apply isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, NA = 6.02214084(18) × 1023 mol−1, is now the most accurate input datum for a new definition of the kilogram.

The possibility of using radioactive sources to measure atomic number Z and the amount of substance nD of unknown objects is considered. An experiment is performed with test samples of different materials exposed to γ-rays from Cs-137 and Co-60 sources. The range of the method’s applicability in measuring atomic number Z and amount of substance nD is shown.

This paper describes principles of a proper dilution of samples used for the determination of antioxidant capacity by means of a photochemiluminiscence method using the instrument Photochem (Analytik Jena AG). The authors used the method ACL (Lipid-soluble Antioxidant Capacity), which is one of two methods enabling to measure in this instrument. It was demonstrated that values measured by the photochemiluminiscence method ACL were influenced by the degree of sample dilution. When studying effects of dilution of samples of wine and rutin, it was demonstrated that there is a non-linear correlation between the degree of dilution and measured values of antioxidant capacity. At low molar amount of substance (i.e. at 0.5 and 1.0 nmol), the measured value of rutin inhibition was higher than the same that molar amount of trolox. At higher molar amounts (i.e. 3; 4 and 5 nmol), the inhibition value of trolox was higher. This dependent change can be explained by means of a different effectiveness of antioxidants and a different stability of their products with radicals.

The concept of mole is an abstract concept of sub-micro level. The main problem in chemistry that should be encounter by educators is students’ inability to transfer understanding between macro level and sub-micro level. Particle-oriented approach is created due to improper expression in the term of mole on books and classroom learning. A mole is the amount of substance of a system, which contains as many elementary entities as there are atoms in 0,012 kg of carbon-12. When the mole is used, the elementary entities must be specified; they may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles. The study presented here focuses on students’ activity and response taught by mole triangle implemented in German and Indonesian classroom. Two classes of grade-10 were involved in each country. The way of students perform in the test was analyzed. Hands-on activities were used as an entrance and followed by particle-oriented expression. In worksheets of each hands-on experience, students should write the correct expression of mole concept. The results of the study indicated that there is different level of understanding in representing knowledge in learning the mole. The use of correct expression will ensure that students see meaningful relationships and can easily go back and forth between macro, sub-micro and symbolic level.

Textbooks still have the distinction of being the most dominant teaching tool in science teaching. The manner in which a scientific concept is expressed in a textbook is of importance in the in-depth learning process of that concept. With this in mind, problems with expressing the “amount of substance” concept were reviewed in 15 chemistry textbooks published in three different countries (United States, France and Turkey). The problems were analyzed in terms of semantic and didactic perspectives. It was found that the semantic mistakes in the presentation of the amount of substance concept in chemistry textbooks stemmed from: (i) missing concepts, (ii) the use of knowledge at the incorrect level, (iii) the use of the term “number of moles”, (iv) limitations in meaning resulting from a lower concept being used in place of a higher concept, and (v) the use of the amount of substance concept as equivalent to mass, Avogadro’s constant, molar volume and molar mass. Additionally, difficulties were observed that arose from the inappropriate didactic transposition of textbook subjects. These didactic difficulties stemmed from associating the amount of substance with more than one physical quantity. Teaching models for meaningfully teaching the amount of substance at the macroscopic, microscopic and symbolic levels of chemistry have been suggested and discussed.

The detection of steroids originating from synthetic precursors against a background of their chemically identical natural analogues has proven to be a significant challenge for doping control laboratories accredited by the World Anti-Doping Agency (WADA). The complementary application of gas chromatography–mass spectrometry (GC-MS) and gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) has been demonstrated to provide specific detection of endogenous steroid misuse for improved anti-doping analysis. Markers of synthetically derived steroids are reviewed on the basis of abnormal urinary excretions and low 13C content. A combinatorial approach is presented for the interpretation of GC-MS and GC-C-IRMS data in the anti-doping context. This methodology can allow all relevant information concerning an individual's metabolism to be assessed in order to make an informed decision with respect to a doping violation. Copyright © 2012 John Wiley & Sons, Ltd.

We consider here two different models describing subdiffusion. One of them is derived from Continuous Time Random Walk formalism and utilizes a subdiffusion equation with a fractional time derivative. The second model is based on Sharma-Mittal nonadditive entropy formalism where the subdiffusive process is described by a nonlinear equation with ordinary derivatives. Using these two models we describe the process of a substance released from a thick membrane and we find functions which determine the time evolution of the amount of substance remaining inside this membrane. We then find ‘the agreement conditions’ under which these two models provide the same relation defining subdiffusion and give the same function characterizing the process of the released substance. These agreement conditions enable us to determine the relation between the parameters occuring in both models.

The study of many biological systems requires the application of a compartmental analysis, together with the use of isotopic tracers, parameter identification and methods to evaluate the mean parameters. For all this, the kinetic equations of the compartmental system as a function of its parameters are needed. In this paper, we present some considerations on the diagrams of connectivity of linear compartmental systems and obtain new properties from the matrix corresponding to the ordinary first-order linear differential equation systems which describe their kinetic behaviour. Using these properties, symbolic equations are obtained in a simplified form. These equations provide the instantaneous amount of substance in any compartment of the system when zero input is injected into one or more of the system compartments, solely as a function of those parameters of compartmental systems which really have an influence on the sought expression. This is unlike what happens in the other symbolic equations obtained in a previous contribution that included all the fractional transfer coefficients involved in the compartmental system, regardless of whether or not they had an influence on the instantaneous amount of substance.

IntroductionDissolution is the amount of substance that goes into solution per unit time under standardised conditions of liquid/solid interface, solvent composition and temperature. Dissolution is one of the most important tools to predict the in-vivo bioavailability and in some cases to determine bioequivalence and assure interchangeability.AimTo compare the differences in dissolution behaviour of solid dosage forms between innovators (reference products) and their generic counterparts (tested products).MethodsFour replicates for each batch of 37 tested medicines was carried out using A PT-DT70 dissolution tester from Pharma Test. A total of 13 branded medicines and 24 generic counterparts were obtained locally and internationally to detect any differences in their dissolution behaviour. They were tested according to the British Pharmacopeia, European Pharmacopeia and the US Pharmacopeia with the rate of dissolution determined by ultra-violet Spectrophotometery.ResultsMost tested medicines complied with the pharmacopoeial specifications and achieved 85% dissolution in 60min. However, some generic medicines showed significant differences in dissolution rate at 60 and 120min. Many generic medicines showed a slower dissolution rate than their branded counterparts such as the generic forms of omeprazole 20mg. Some showed an incomplete dissolution such as the generic form of nifedipine 10mg. Other generics showed faster dissolution rate than their branded counterpart such as the generic forms of meloxicam 15mg. Moreover, some generics from different batches of the same manufacturer showed significant differences in their dissolution rate such as the generic forms of meloxicam 7.5mg. Nevertheless, some generic medicines violated the EMA and the FDA guidelines for industry when they failed to achieve 85% dissolution at 60min, such as the generic form of diclofenac sodium 50mg.ConclusionMost medicines in this study complied with the pharmacopeial limits. However, some generics dissolved differently than their branded counterparts. This can clearly question the interchangeability between the branded and its generic counterpart or even among generics.

Amount of substance is one of the base quantities that form the International System of units. The quantity measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons and other particles. In order to count atoms with a relative uncertainty of better than 2 × 10−8, here we formulate the amount of substance measurement homogeneity principle. A consequence of this principle is that the accuracy of a measurement of amount of substance is limited by the homogeneity of the sample. We propose a criterion of sample preparation for the accurate determination of molar mass which is to ensure complete chemical conversions, no fractionation, homogeneity at the molecular level and less contamination. Based on this philosophy, a more accurate molar mass of natural single crystal silicon was achieved. We found that there was an isotope fractionation in the preparation process of the NaOH solution method. It led to an Avogadro constant value 1.0 × 10−6 lower. The corrected value is higher than previous data, and compatible with recent values of the Planck constant.

The Avogadro constant, the number of entities in an amount of substance of one mole, links the atomic and the macroscopic properties of matter. Since the molar Planck constant—the product of the Planck constant and the Avogadro constant—is very well known via the measurement of the Rydberg constant, the Avogadro constant is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a new definition of the kilogram in terms of a fundamental constant. Here, we describe a new and unique approach to determine the Avogadro constant from the number of atoms in 1 kg single-crystal spheres that are highly enriched with the 28 Si isotope. This approach has enabled us to apply isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, N A =6.022 140 82(18)×10 23 mol −1 , is now the most accurate input datum for a new definition of the kilogram.

The mole is the most recent addition to the set of base units that form the International System of Units, although its pre-cursor the ‘gram-molecule’, had been in use by both physicists and chemists for more than 120 years. A proposal has been published recently to establish a new definition for the mole based on a fixed value for the Avogadro constant. This would introduce consistent relative uncertainties for the molar and the atomic masses while making no change to the system of relative atomic masses (‘atomic weights’). Although the proposal would have little impact on the measurement uncertainty of practical work, it has stimulated considerable debate about the mole and the nature of the quantity amount of substance. In this paper, the rationale for the new definition is explained against the background of changes in the way the quantity amount of substance has been used, from its first use during the early development of thermodynamics through to the use of the ‘number of gram-molecules’ at the end of the nineteenth century.

The fundamental concept of the mole stems from the idea of the gram-atom (or gram-molecule): that an amount of one mole of a given substance has an associated mass, in grams, numerically exactly equal to the relative atomic (or molecular) mass of the substance. This means that the particular number of entities comprising one mole, Avogadro’s number, must be exactly equal to the gram-to-dalton mass ratio. Various interpretations of what a mole actually means and how this affects the ideal gas equation depend on how the amount of a given substance, n, is related to the corresponding number of entities, N. We look at three alternatives: (1) the conventional interpretation in which n is directly proportional to N, where the proportionality factor is the reciprocal of the (evidently poorly understood) Avogadro constant; (2) a more easily comprehended alternative in which n is equal to N entities; and (3) an interpretation in which n and N both represent the number of entities, but expressed in different ways. Regardless of these different interpretations, the form of the stoichiometric equations (relating N, n and the total sample mass) and the form of the relationship between the universal gas constant and the Boltzmann constant remain the same.

In this paper, it is argued that the SI system has not carefully enough taken into account the differences that exist between stoichiometry and physics, and because of this neglect forced the kind-of-quantity amount of substance into a false form. The mole is not a unit such as the metre, the kilogram, and the second. It is a “unit” only in the sense in which purely mathematical scaling factors can be called units.

There is a common misconception among educators, and even some metrologists, that the Avogadro constant NA is (or should be) a pure number, and not a constant of dimension N?1 (where N is the dimension amount of substance). Amount of substance is (and always has been) measured as a ratio of other physical quantities, and not in terms of a specified pure number of elementary entities. Hence the Avogadro constant has always been defined in terms of the unit of amount of substance, and not vice versa. The proposed redefinition of the mole in terms of a fixed value of the Avogadro constant is examined, and it is shown that such a redefinition would not bring any significant metrological benefit. It is contended that such a redefinition would only add to the confusion in this field, and so should be rejected.

Neutron activation analysis (NAA), based on the comparator method, has the potential to fulfill the requirements of a primary ratio method as defined in 1998 by the Comite Consultatif pour la Quantite de Matiere — Metrologie en Chimie (CCQM, Consultative Committee on Amount of Substance — Metrology in Chemistry). This thesis is evidenced in this paper in three chapters by: demonstration that the method is fully physically and chemically understood; that a measurement equation can be written down in which the values of all parameters have dimensions in SI units and thus having the potential for metrological traceability to these units; that all contributions to uncertainty of measurement can be quantitatively evaluated, underpinning the metrological traceability; and that the performance of NAA in CCQM key-comparisons of trace elements in complex matrices between 2000 and 2007 is similar to the performance of Isotope Dilution Mass Spectrometry (IDMS), which had been formerly designated by the CCQM as a primary ratio method.

A general discussion of the redefinition of the mole, the SI unit for ‘amount of substance’, is now ongoing in ever broadening circles as part of a general overhaul of the Systeme International d’Unites, SI. Important for chemists are the unit mole (symbol mol) and the unit kilogram (symbol kg). For several thousands of years, ‘mass’ was the property enabling measurement of ‘‘how much is there?’’ by using a comparative balance and the property of masses on the surface of the earth commonly called ‘‘weight’’ (concepts put in single quotes; double quotes used for quotations or to emphasize). Then, Isaac Newton (1642–1727) fundamentally changed our thinking by explaining that ‘mass’ was related to both ‘gravitational attraction’ and ‘inertia’. Einstein (1879–1955) further showed that these are the same quantity. Quite different to this is the modern concept of ‘amount of substance’ mentioned in the SI but basically different from each of these. Equally important is the concept ‘number of particles’ (in generic language: ‘number of entities’; ‘entities’ here must be specified), based on the property of ‘numerosity’ [1]. It is present in the mind of chemists making analytical measurements. ‘Mass’ was included in the International System of Quantities (ISQ) as a base quantity (Sect. 1.2 pp 104–105 in [2] and entry 1.6 in the Vocabulaire International de Metrologie—VIM [3]), and assigned the base unit kilogram. ‘Numerosity’ was not. Neither was ‘number of entities’. This disregarded the discontinuous structure of matter. In 1971, the Conference Generale des Poids et Mesures (CGPM), on the proposal of the Comite International des Poids et Mesures (CIPM) and without a consultative committee on chemical measurements in existence (that Committee started to be operational in 1996 only), decided to define a unit ‘‘mole’’ as follows (see Sect. 2.1.1.6 p 115 in [2])

‘Amount of substance’ was introduced in the end of the 1950s as the physical quantity whose unit of measurement is the mole. Fundamental problems associated with this physical quantity have caused a never-ending discussion that continues to this day. One of the reasons for this is the fact that the expression ‘amount of substance’ is not a good choice, due to its generality and inclusion of the word ‘substance’. Considering that samples of matter commonly handled by chemists are extremely numerous in entities and that the quality of being numerous or many is referred to as numerosity (a concept related to numerical cognition), this concept is reproposed as a replacement for amount of substance. Then, taking into account ongoing discussions toward a redefinition of the mole, the following definition is proposed for this SI base unit: “the mole is the numerosity of a sample of entities numbering exactly 6.022 141 794 × 1023”. The relationships between four extensive properties of matter (mass, volume, numerosity and number of entities) are detailed and the resulting intensive physical quantities (proportionality constants) are discussed. The concept numerosity is not the product of an invented synonym; furthermore, as a consequence of its generality, it can be used to express the quantity of entities in samples of matter, as well as of light, chemical reactions, etc. The acceptance that mole is the SI unit of numerosity might also solve most of the pedagogic problems associated heretofore with teaching of mole and amount of substance.

Most base units in the SI relate to specific sensoric qualities our body is able to observe: space, heat, brightness, etc. The base unit ‘mole’ incorporates intellectual insight: the atomistic perception of the world. This perception is a quintessence of over 300 years of scientific research. The quintessence, from Dalton’s ‘The sceptical chymist’ to Perrin’s Nobel Prize in 1926 and Pauling’s ‘Nature of the Chemical Bond’ in 1939, results in the conclusion that the base unit of the SI quantity ‘amount of substance’ is not the mole but the dimensionless entity.

It is shown here that five base quantities (and the corresponding five base units) of nature are sufficient to define all derived quantities (and their units) and to describe all natural phenomena. The base quantities (and their base units) are: length (m), mass (kg), time (s), temperature (K) and electric charge (C). The amount of substance (mole) is not taken as a base quantity of nature and the Avogadro constant is not considered as a fundamental constant of nature, as they are both based on an arbitrary definition (due to the arbitrary value of 0.012 kg for the mass of 1 mole of C-12 isotope). Therefore, the amount of substance (mole) is moved from the list of base quantities to the category of the supplementary units (to be re-created after its abrogation in 1995). Based on its definition, the luminous intensity (cd) is not a base quantity (unit), therefore it is moved to the list of derived quantities (units). The ampere and coulomb are exchanged by places in the list of base and derived units, as ampere is a speed of coulombs (but SI defines meter, not its speed as a base unit). The five base quantities are re-defined in this paper by connecting them to five fundamental constants of nature (the most accurately known frequency of the hydrogen atom, the speed of light, the Planck constant, the Boltzmann constant and the elementary charge) with their numerical values fixed in accordance with their CODATA 2006 values (to be improved by further experiments).

Common student misunderstandings regarding chemical equilibrium are reported taking into account the response of freshman students to some typical questions involving acid-base reactions. Language has been shown to be one of the main issues associated with students' difficulties on this subject, such as in the case of concentration and amount of substance (mol). Another usual problem was observed in questions involving buffer solutions after addition of a reagent. A number of recommendations have emerged from the results presented in this work as an attempt to enhance the learning of this topic in general chemistry courses given to first-year students.

CCQM, the ‘Consultative Committee on amount of substance—metrology in chemistry’ to the International Committee for Weights and Measures (CIPM), is being renamed ‘CC on amount of substance—metrology in chemistry and biology’. This seems to be an excellent occasion to review the status of the understanding of the concept ‘amount of substance’ in the chemical community at large. It is broadly admitted that the concept (and term) ‘amount of substance’ has been a source of confusion ever since it was used in the International System of Units (SI) in 1971 by the General Conference on Weights and Measures (CGPM) as the base quantity for the definition of the unit mole [1]. Thus, the International Organization for Standardization (ISO) through its Technical Committee 12, responsible for quantities, added it as such to the International System of Quantities, ISQ [2]. It was also included in the 2nd and 3rd edition of the International Vocabulary of Metrology [3, 4]. The term mole had been in existence for a very long time (almost a 100 years), albeit subject to various interpretations. However, there is a long-standing problem. A unit—of necessity—requires a quantity of which it is the unit: the kilogram is the unit of the quantity ‘mass’, the second is the unit of the quantity ‘time’, the metre is the unit of the quantity ‘length’, etc. The absence of a clearly understood and accepted description in the chemical community of the quantity ‘amount of substance’ having the unit mole, especially in the analytical community, was—and still is—a problem. That is not good. Sometimes, ‘amount of substance’ is simply described as ‘the quantity of which the mole is the unit’ [5, 6], a description from which we do not really learn very much. Neither is the text in a well-known textbook helpful wherein it is stated that ‘The mole is an SI base unit ... The physical quantity to which it refers is called the ‘amount of substance’, n. However, practicing chemists commonly prefer to talk about the number of moles. Take the advice of your instructor on whether to use or not the official term’ [7]. A very worthwhile attempt was already made in 1990s to replace the term ‘amount of substance’ by ‘numerosity’ [8], a term for indeed a property of matter (see definition of ‘quantity’ in [3, 4]) that stresses the fact that matter is discontinuous in structure and consists of discrete entities. It was not disapproved in the literature (on the contrary) nor considered and replied to in the ‘New SI’ [9]. Rather ‘amount of substance’ was kept, stressing a continuous character as property of matter, a property that was disqualified by modern science since more than a hundred years. Also, the ‘Reproposition’ [10] of the suggestion underwent the same fate rather than be examined seriously. Hence, let us attempt to understand—or at least attempt to clarify some problems—with the SI quantity ‘amount of substance’. Around 1990s, the need for ‘traceability of chemical measurement results to the SI’ started to take off in the literature because there was a rising need to compare measurement results across borders in trade, in commerce, in food and feed measurements, in environmental and clinical measurements, in international and intercontinental interlaboratory comparisons, to name just a few. Also, The author is a member of the Joint Committee on Guides for Metrology (JCGM), Working Group 2 (VIM). The opinions expressed in this column do not necessarily represent the view of the Working Group or of ACQUAL.

Existing research has demonstrated the significance of situational antecedents to substance use. The current study used a cluster analytic approach to identify groups of club drug users who report using substances in similar situations (assessed by the Inventory of Drug Taking Situations) with longitudinal data from 400 active drug users. A three-cluster solution emerged in baseline data and was replicated in 12-month follow-up data. Groups were identified as Situationally Restricted, Pleasure Driven, and Situationally Broad users. Group differences were observed on measures of mental health, attitudes towards substance use, amount of substance use, and rates of substance dependence. Cluster membership predicted substance dependence after controlling for past dependence, current use, and current depression/anxiety.

Proposals on the floor at CIPM are aiming at defining basic units by stipulating a consensus value for a number of fundamental constants. The paper indicates the author’s viewpoint about a number of issues that, in his view, should be better understood before such a choice becomes indisputable. They include the count nature of the Avogadro number; the correct expression of its stipulated numerical value; the check for the consistency of the SI system; the shift to the unit of the experimental uncertainty; the loss of the concept of base unit; the possibility of checking the correctness of the future standards; implications for the future reductions in uncertainty; the meaning of ‘fundamental’ related to the constants; and some lexical problems.