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In this paper I take a close look at the SI base quantity “amount of substance”, and its unit, the mole. The mole was introduced as a base unit in the SI in 1971, and there is currently a proposal to change its definition. The current definition of the mole shows a certain ambiguity regarding the nature of the quantity “amount of substance”. The proposed new definition removes the ambiguity, but at a cost: it becomes difficult to justify treating amount of substance as having its own dimension, and hence its own unit, the mole. I argue that the difficulties with amount of substance result from its role as a mediator between macroscopic and microscopic scales. To understand why amount of substance might have its own dimension, we need to connect amount of substance to mass, contra current proposals to separate them.

New definitions of the units for amount of substance – the mole – and for mass – the kilogram – will presumably come into force on the World Metrology Day 2019. In the revised SI, the mole will be defined by a fixed value of the Avogadro constant and the kilogram by a fixed value of the Planck constant. The X-ray-crystal-density (XRCD) method has been used for the determination of these fundamental constants by counting the number of atoms in 28Si-enriched spheres. Thus, silicon spheres will – after the redefinition – be used to realize the definitions of the mole and the kilogram. This is possible by SI-traceable measurements of lattice parameter, isotopic composition, volume, and surface properties, yielding a relative standard uncertainty below 2⋅10−8. Whereas this high accuracy is only reached with isotopically enriched silicon, it is also planned to use natural silicon spheres on a slightly lower level of accuracy. The future definitions will allow also new realization methods using silicon, in particular for small mass values.

Fractal is a set owning an infinitely fine structure in a self-similar or self-affine way covering all scales, and is widely used to model the structure of porous media. Hydrate-bearing sediments belong to porous media, so this paper attempts to construct a structure model of hydrate-bearing sediments with the three-component fractal extended from the two-component fractal. The three-component fractal is capable to display structural details at arbitrarily small scale. Additionally, in the three-component fractal, any parameter defined as the ratio (such as porosity and hydrate saturation) of two different volumes approaches a determined value when considering the infinitesimal scale. The interface between hydrate elements and pore elements is suggested to be a potential way to classify the hydrate-bearing sediments. Using the proposed three-component fractal model to calculate the interface between one arbitrary hydrate particle and surrounding pores, we obtain the theoretical solutions of the amount of substance, the dissociation rate and maximal dissociation time of one arbitrary hydrate element in sediments. It is found that the effective reacting surface of one hydrate element in sediments could be equal to even greater than that of the pure hydrate element in the late period of hydrate dissociation, during which the amount of substance of one hydrate element in sediments is still greater though. Finally, we further extend the three-component fractal to any-component fractal, and show how to model more complex porous media by using a suitable generator.

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.

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.

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.

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.

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.

Traditional XPS imaging produces a map of the XPS peak intensity. It is well known that the peak intensity carries limited information on the total amount of material as well as on the depth distribution of atoms. Such images can therefore be strongly misleading. Elaborate methods for improved quantification by analysis of the peak shape were developed by Tougaard et al. in the past but they require operator interaction and are therefore not suitable for imaging where thousands of spectra must be analyzed. Recently, Tougaard proposed a new algorithm [S. Tougaard, J. Vac. Sci. Technol. A 21 (2003) 1081] which is less accurate but sufficiently robust to allow for automatic data processing. In the present paper, we have successfully demonstrated the ability of the algorithm to produce detailed images of a plasma patterned polymer on Teflon. In general, four images are produced which show the distribution of pixels where F atoms are at the surface, in the bulk, or homogeneous in depth as well as an image of the amount of F atoms within the outermost three inelastic electron mean free paths.

Measurement is the process of determining a correct value of a measurand; definition of the measurand is decisive for an expedient choice of a measurement method. The result of a measurement refers in principle only to the amount of substance actually contributing to the analytical signal. An appropriate definition of the measurand, however, must include a specification of the entire system, for which the result of the measurement is required to apply, i.e., which it is supposed to represent. The concept of representativity therefore assumes importance for the metrological quality of a measurement, and the process with which to ascertain representativity is proper sampling. All systems from which a sample is to be selected are inherently heterogeneous (this is only a matter of the scale of observation), and it is therefore necessary to take into account a contribution from this characteristic, when expressing the uncertainty of the reported value of the measurand. Examples are presented, where methods from metrology are combined with the Theory of Sampling to evaluate the influence of sampling on the uncertainty of results obtained by the analysis of biological materials.

In this contribution, we present the symbolic time course equations corresponding to a general model of a linear compartmental system, closed or open, with or without traps and with zero input. The steady state equations are obtained easily from the transient phase equations by setting the time → ∞. Special attention has been given to the open systems, for which an exhaustive kinetic analysis has been developed to obtain important properties. Besides, the results have been particularized to open systems without traps and an alternative expression for the distribution function of exit times has been provided. We have implemented a versatile computer program, that is easy to use and with a user-friendly format of the input of data and the output of results. This computer program allows the user to obtain all the information necessary to derive the symbolic time course equations for closed or open systems as well as for the derivation of the distribution function of exit times.

Two synthetic isotope mixtures for the calibration of sulfur isotope amount ratio measurements were gravimetrically prepared from high purity Ag2S materials enriched in 32S, 33S, and 34S. The mixtures were made so as to closely resemble the (natural) isotopic composition of the materials to be “calibrated”. This allowed a totally independent evaluation, on the same samples, of the relative combined uncertainty of: (a) the procedure to perform direct measurements of the amount of substance ratios of gas isotopes in the redetermination of the Avogadro constant and (b) the gravimetric preparation procedure. The result of both procedures, mass spectrometry and gravimetry, agree to a relative uncertainty of 3 × 10−4 for sulfur amount ratio measurements of the major abundant isotopes. Thus it seems that a direct measurement of isotopic gas mixtures (e.g. of natural isotopic composition) is now possible for sulfur—and probably also for other gaseous isotopes—without necessarily having to rely on “calibration” by means of values provided by measurements of gravimetrically prepared isotope mixtures. However, synthetic mixtures may be needed for validation and verification purposes, in particular for quality assurance.

Mathematical treatment of diffusion with the second Fick's equation is only feasible when the amount of substance transferred is so low that the change in dimension is negligible. A more general theory of diffusion is established in the case of a sphere by considering the radial diffusion and the subsequent change in dimension, with an infinite coefficient of surface matter transfer. The problem is studied in the case of absorption-desorption histories, by considering various values of the maximum relative volume expansion, this maximum being obtained when the sphere is saturated by the substance.

According to provisions of IUPAC, SI and ISO the concept of equivalence should be abandoned, due to its shortcomings. The equivalent weight of a substance cannot be uniquely defined. The equivalence law applies only to acid-base and oxidation-reduction titrations, and does not apply to complexometric and precipitation titrations. This paper presents a rule of equal amount of substance to solve the problems of the equivalence law.

The relation between pressure and amount-of-substance density of {(1- x )CO 2 + x H 2 } at temperatures 303.15 K 343.15 K and at temperature up to 12.7 MPa is reported. Second and third virial coefficients from experimental results are obtained after a virial-equation fit. Unlike-interaction second virial coefficients are compared with known values in the literature. Unlike-interaction third virial coefficients are also presented, using the model suggested by McGregor et al .

A more realistic comparison than otherwise of crystallization rates of different electrolytes in solution is obtained if supersaturation is represented by the product of the thermodynamic driving force and the amount of substance which may crystallize from unit volume of supersaturated solution. The entropy production per unit area of crystal surface for a given value of this supersaturation parameter is closely related to the chemical nature of the growing crystal and the growth mechanism. This may be used to predict growth rates and growth mechanisms.

The amount of substance that can be separated per unit time (the production rate) and the purity of the isolated compounds are the determining quantities in preparative chromatography. Basing the design and operation of a preparative system on the optimal production rate means optimizing the latter with respect to time, solvent consumption and the smallest possible dilution of the sample in the effluent. Equations describing the influence of the process variables are derived showing as the most important and striking result that the production rate is not a linear function of the column length. They predict that working under conditions where the contribution to mass dispersion of the injected volume and the column itself are about equal is to be preferred. The influence of the pressure limitation and pumping capacity of a chromatographic system on the production rate is discussed.

The theory of Kubelka and Munk is evaluated for simultaneous measurement of reflectance and transmittance as a densitometric method. A relation yielding the amount of substance in a t.l.c. spot, as a function of its reflectance and transmittance, is derived. A densitometer operating according to this relation is described. To check the validity of the derived relation, measurements were made on spots of Sudan yellow developed with chloroform on silica layers. The results show a satisfactory proportionality between apparatus response and amount of substance applied.

An improvement of WRIGHT'S method for the determination of molecular weights is described, in which the filterpapers, carrying the solutions, are handled and weighed in light aluminium rings, and equilibrium is reached inside a closely fitting aluminium box. There is a wide choice of appropriate solvents with boiling points ranging from 100–184°. The accuracy reached is 5–10%. The amount of substance required is about 1 mg.

The technique of incorporating the substance in a sintered disc of potassium bromide seems to be very promising for quantitative analysis of solid substances by infrared absorption. By this method, the amount of substance used may be known precisely; however, it has been shown experimentally that in the case of powdered calcite, the extinction depends very largely on the particle size of the dispersed substance. A theoretical expression is given which agrees with the experimental observations.

Since it was first discovered that cell elongation in the Avena coleoptile is controlled by a hormone, our understanding of the nature and role of this substance has progressed considerably. Apart from the elucidation of its functions in promoting growth, tropisms, and other reactions of the plant, the chemical nature of the substance has been extensively studied. The active substance produced by cultures of the mold Rhizopus suinus was shown by Nielsen (1930) to be ether-soluble, and by Dolk and Thimann (1932) to be an unsaturated organic acid, decomposed by strong acids but not by alkalies, and readily inactivated by oxidation. Its dissociation constant, as measured by Dolk and Thimann, is 10^-4.75. Previously, Went (1928) had shown the molecular weight of the active substance in Avena coleoptiles to be about 376. The active substance in human urine was isolated by Kogl and Haagen-Smit (1931) and by Kogl, Haagen-Smit, and Erxleben (1933), and shown to be an acid, C17H28O(OH)COOH (auxin A), whose lactone is also active, while from malt these workers later isolated (1933) a ketohydroxy acid, C17H28O(OH)COOH (auxin B), which had the same activity per unit weight. On account of the rather small amount of substance available from Rhizopus cultures, and also since the bulk of the partially purified product was lost through spontaneous inactivation (see section, “Concluding stages”), the chemical investigation of the active substance, begun earlier, was dropped. However, the many experiments on purification which had meanwhile been carried out showed that the active substance from Rhizopus did not behave in quite the same way as that from urine. Recently, however, it was shown by Kogl, Erxleben, and Haagen-Smit (1934) that there is in urine a second active substance, identical with β-indolylacetic acid, and Kogl and Kostermans (1934) showed that the molecular weight of the substance produced by Aspergillus and by Rhizopus is that of β-indolylacetic acid rather than that of the C18 compounds. Since preparations from Rhixopus have been extensively used for physiological work, both in this laboratory and elsewhere, the exact nature of the active substance is of considerable interest. The present paper will give evidence that the active substance produced by Rhizopus suinus is in fact β-indolylacetic acid. Identification by the preparation of derivatives and by mixed melting points with the pure synthetic substance was not possible on account of the small amount of material available. Nevertheless, the evidence given below is fairly conclusive. The method of purification, since it differs to some extent from that adopted by Kogl and his coworkers, will also be outlined. Finally, it will be shown that some of the peculiar conditions previously found to be necessary for the production of this growth substance (Thimann and Dolk, 1933) find a simple explanation on this basis.

A technique for the quantitation of flat-bed chromatograms or electropherograms involving the minimum exposure time necessary for a spot just not to appear on a photograph has been developed. For calibration purposes the minimum exposure time is plotted against the amount of substance spotted. The amount of a substance present in an unknown spot is determined from the minimum exposure time. The procedure is inexpensive, simple and particularly suitable for occasional quantitations.

The use of classical moving boundary electrophoresis in the study of biopolymers has decreased substantially in recent years. Among the reasons for its loss of popularity are the high cost of the equipment, the complexity of the technique, and the large amount of substance necessary for an analysis. Nevertheless, moving boundary electrophoresis remains the method of choice for the determination of the mobility-pH curve of a biopolymer (1), for as pointed out by Kunkel (2) zone methods are incapable of providing absolute mobilities. The present note describes an extension of the capabilities of the moving boundary method to the determination of mobilities of a biologically active principle at very low concentrations and contained within an impure mixture. The procedure in our new method is similar in principle to that used to determine sedimentation coefficients with a partition cell in an analytical ultracentrifuge (3,4). In the latter technique, the quantity of active substance sedimented across a fixed plane in the cell is measured, generally by a specific sensitive analysis of the biological activity on one side of the partition relative to that in the original solution. An analogous procedure is described here for determination of electrophoretic mobilities in a moving boundary apparatus.

A flexible computer program was set up to simulate the kinetics of the amounts of radioactivity and the amounts of substance in various classes of nucleic acids for a generalized biological system. This program works by transferring numbers from registers to other registers corresponding to the amounts of isotope label or the amount of substance moving from one pool or compartment to another for each successive time interval. It is practical to choose the time interval small enough so that the same results are accurately obtained with this type of computation as with the analytical solution for the most realistic and complicated case previously formulated. Much more complicated situations now can be treated with this recursion program and questions of relevance to current molecular biology can be answered. The questions treated in this paper are directed to enteric microorganisms and are as follows. (1) What are the conditions under which a short pulse reflects net synthesis and what are the conditions where it reflects total synthesis? (2) What are the conditions that measurement of intermediate pool specific activity can yield information about the turnover and concentration of unstable macromolecules in the system? (3) How prolonged can a pulse be and still label the species of RNA substantially in proportion to their rates of synthesis? (4) What are the amounts and rates of synthesis and degradation of ribosomal precursors best fitting data in the literature?

A systematic investigation of the extinction of flames by fine powders propagating in a tube, carried out on various propagation regimes ranging from uniform, flames to detonations, has shown that each flame is best inhibited by a substance of optimum particle diameter, variable with the flame parameters. Additional chemical specificity can result only after the convenient particle diameter is correctly chosen. This second stage of the inhibition process can sometimes drastically reduce the amount of substance necessary to produce extinction. In the cases where a chemical specificity is noted, alkaline salts appear to be more efficient when decomposition, fusion or volatilization is likely to occur at low temperature.

Radioisotopes can serve as a suitable tool for the study of diffusion in polymers. Two different methods have been used for this purpose: radiometric measurements, which enable us to determine the total amount of substance diffused into polymers and to compute diffusion coefficients, and autoradiographs, which can yield the distribution of substances in polymer and also the local concentration of diffused substances.