The most challenging problems in the field of chemico- and bioanalytical measurements are described. These problems are being solved, in particular, by participating in new international comparisons ...organized by the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology of the International Committee of Weights and Measures (CCQM CIPM). Solutions of these challenging problems are presented. The objectives and tasks of developing key comparisons in the following areas are described: isotopic measurements; determination of the purity of substances; organic analysis; bioanalytical measurements; measurements of aerosol particle parameters; measurements in the field of gas analysis and electrochemistry. It is shown that participation in international key comparisons allows obtaining valid and reliable results of measurements of the composition and properties of gas and liquid media, as well as solid substances and materials.
•Vapor pressure of 75 pure substances was modeled by a new accurate method.•Model was compared with five mostly used equations include Antoine and Wagner model.•Results showed that new model is more ...accurate than other models with 0.091% AARD.
Accurate liquid–vapor pressure prediction is fundamental to develop equations of state to simulate, evaluate and optimize chemical processes. The accuracy of vapor pressure calculations is essential because it is used as a basis to calculate the acentric factor, thermal and equilibrium properties. In this study, a new accurate equation for calculate the vapor pressure of pure substances as a function of reduced temperature and critical pressure is presented by using Marquardt–Levenberg algorithm which minimize the sum of the squared differences between the values of the observed and predicted values of the dependent variables.
Vapor pressures have been calculated with presented substance-dependent equation and compared with the data reported in data compilation for 75 pure substances for more than 15,000 data points, and the overall average absolute percentage deviation is only 0.091%. The accuracy of obtained model has been compared to the mostly used equations and the comparison indicates that the proposed method provide more accurate results than other methods used in this work.
An information system has been designed for monitoring the quality of chemical reagents and high-purity substances. The information system is based on the international CALS standard (ISO-10303 ...STEP). It contains the following information for the main elements of analytical monitoring: a list of elements to be monitored (substance classifier), details of the analytical procedure (including the sampling and sample preparation steps), performance parameters of the instruments, metrological support, and normative documentation (GOST standards, technical specifications, and others).
A pure material proportion estimation method based on a spectral database is proposed. The method transforms the non-negative and linear constraints into a pure material proportional cost function ...minimization problem with a linear mixed model. The Newton algorithm is used to optimize the cost function, and the optimized extreme value is the optimal estimate of the proportion of pure material. Spectral simulation experiments are carried out for space target materials using the US Geological Survey database, and the experimental results show that the method proposed in this paper can help to estimate the proportion of pure substances in such targets quickly and accurately, especially when the number of mixed pure materials is large. Compared with some existing common algorithms, the proposed method is robust and can estimate the proportion of pure material in a space target when the signal-tonoise ratio is less than 40 dB. The accuracy of the method is 30% higher than that of the existing method.
Analysis revealed, that in the area of chemical composition measurements high-purity substances may be regarded as the best measurement capabilities in the database of the International Bureau of ...Weights and Measures. Until now none of the countries of the world has the complete collection of high purity substances with evaluated purity level. At the present time the development of high-purity substances with evaluated values of mass fractions of the base substance is intensively going on to ensure metrological traceability to SI units using both primary methods and other instrumental methods of analysis.
The heat of vaporization of a pure substance at its normal boiling temperature is a very important property in many chemical processes. In this work, a new empirical method was developed to predict ...vaporization enthalpy of pure substances. This equation is a function of normal boiling temperature, critical temperature, and critical pressure. The presented model is simple to use and provides an improvement over the existing equations for 452 pure substances in wide boiling range. The results showed that the proposed correlation is more accurate than the literature methods for pure substances in a wide boiling range (20.3–722K).
The problem of water determination in the creation of pure substances and new functional materials with a low moisture content is considered. The structure, metrological characteristics, and ...prospects of application of the state primary standard of mass fraction and mass (molar) concentration of water in solid and liquid substances and materials GET 173-2013 are presented. Examples of developing thermogravimetric and chemical analyses are provided.
Nueva correlación generalizada para estimar la presión de vapor Cardona Palacio, Luis Fernando
Revista cientifica del Centro de Investigaciones y Desarrollo Cientifico de la Universidad Distral Francisco Jose de Caldas,
2016, Letnik:
25, Številka:
2
Journal Article
Recenzirano
Odprti dostop
In this work, a new generalized correlation for pure substances is proposed for the estimation of vapor pressure, applicable in wide temperature range. Was used equilibrium liquid-vapor data with 28 ...refrigerants and minimizing the sum of the squares of the relative deviation in liquid-vapour pressure were determined the parameters and constants characteristics of the new equation and generalized for any pure substance using the acentric factor. Vapor pressure predictions were made for 45 pure substances who they didn´t not participate in the minimization, generated percent relative average deviation of 1.6073%. The results were compared with others equations for calculating the vapor pressure and the comparison indicates that the proposed method provide more accurate results than other methods used in this work. Finally, the calculations of enthalpies of vaporization were done with deviations of 0.880% and the Waring criterion was applied to check the constants presed in this paper
En el presente trabajo se propone una nueva correlación generalizada para el cálculo de la presión de vapor de sustancias puras. A partir de datos de equilibrio líquido-vapor de 28 refrigerantes y mediante minimización de la suma de los cuadrados de las desviaciones relativas de la presión de vapor, se determinó los parámetros y constantes característicos de la nueva ecuación y a partir del factor acéntrico se generaliza para cualquier sustancia pura. Se evaluó en 45 sustancias puras que no participaron en la minimización, generando porcentajes de desviación relativas promedio de 1.6073%. Se comparan los resultados obtenidos con otros modelos para el cálculo de la presión de vapor y los resultados indican que la nueva ecuación propuesta genera una mejor precisión. Finalmente se calculan entalpías de vaporización con desviaciones del 0.882% y se aplica el criterio de Waring con el fin de comprobar las constantes presentadas en la investigación.
A predictive vapor-pressure equation Velasco, S.; Román, F.L.; White, J.A. ...
The Journal of chemical thermodynamics,
05/2008, Letnik:
40, Številka:
5
Journal Article
Recenzirano
A simple equation is presented for predicting the temperature dependence of the vapor-pressure of a pure substance along the entire (liquid
+
vapor) coexistence curve, from the triple point to the ...critical point. The proposed equation is based on the use of a dimensionless temperature reduced by using critical and triple point values, and of the Clausius–Clapeyron equation as a zeroth-order approximation. The pressure and temperature at the triple point, the normal boiling temperature, and the pressure and temperature at the critical point are required as input data. The proposed equation is verified for 53 fluids by using NIST data. These data are reproduced with an overall average deviation of 0.55%.
Se revisa y evalúa la ecuación de estado quíntica propuesta por Koziol (Koziol, 2008). Se implementa el método de Bairstow para hallar numéricamente todas las raíces del factor de compresibilidad. El ...artículo original no presenta un método para identificar las raíces correspondientes al líquido y al vapor. Se propone un procedimiento con base en el cálculo del coeficiente de fugacidad de cada una de las fases para identificar las raíces correspondientes al líquido y al vapor. Se desarrolla un complemento de EXCEL que permite calcular el coeficiente de fugacidad, el factor de compresibilidad y la presión de vapor a partir de los parámetros de la ecuación y las variables apropiadas. Los resultados obtenidos para diversas sustancias muestran un ajuste aceptable similar al de ecuaciones cúbicas de estado populares. Se demuestra que dichos resultados discretos se deben a la manera en que se determinan los parámetros de la ecuación. Se plantea una nueva manera para determinar dichos parámetros.
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