Calculation of retention indices in programmed-temperature gas chromatography by improved linear interpolation

In order to determine the retention indices of compounds in programmed-temperature gas chromatography as precisely as possible, a series of hydrocarbons having successive carbon numbers is mixed with the solution. The addition of reference products to complex mixtures often results in peak interferences; by adding paraffins with even carbon numbers only, the risk of overlapping of peaks diminishes at the expense of precision. This paper describes a method of improved linear interpolation which gives reliable results of the same accuracy as would have been obtained if the whole series of alkanes had been added. Computer programs have been designed for calculations based on linear as well as improved linear interpolations in on-line and off-line applications.     

Prediction of programmed-temperature retention values of naphthas by artificial neural networks

It is proposed for the first time a method of prediction of the programmed-temperature retention times of components of naphthas in capillary gas chromatography using artificial neural networks. People are used to predict the programmed-temperature retention time using many formulas such as the integral formula, which requires that four parameters must be determined by calculation or experiments. However the results obtained by the formula are not so good to meet the demand of industry. In order to predict retention time accurately and conveniently, artificial neural networks using five-fold cross-validation and leave-20%-out methods have been applied. Only two parameters: density and isothermal retention index were used as input vectors. The average RMS error for predicted values of five different networks was 0.18, whereas the RMS error of predictions by the integral formula was 0.69. Obviously, the predictions by neural networks were much better than predictions by the formula, and neural networks need fewer parameters than the formula. So neural networks can successfully and conveniently solve the problem of predictions of programmed-temperature retention times, and provide useful data for analysis of naphthas in petrochemical industry.     

Nucleation of one polymorph by another

Nucleation of one polymorph by another has been observed directly in the melt crystallization of d-mannitol and d-sorbitol. The new polymorph nucleated on an existing one and grew to dominate the end product. This effect is relevant to controlling polymorphism in the manufacture of specialty chemicals and to developing theories of polymorphic nucleation and concomitant polymorphs, for which current efforts emphasize homogeneous nucleation of alternative polymorphs.     

Determination of retention indices in LPTGC

Summary A method is presented for the calculation of retention indices in linear programmed-temperature gas chromatography (LPTGC) on the basis of isothermal retention data and the operating conditions (initial temperature, programming rate, gas flow velocity) of the run. Part IV of a series; parts I, II and III see refs. [1], [2] and [3].     

Calculation of retention indices at an assigned temperature from temperature-programmed data

Summary A method is presented for the calculation of retention indices at an assigned temperature from temperature-programmed data. If the retention times at two different program rates for the solutes and the n-alkanes are known, the retention indices at an assigned temperature can be calculated directly.     

A method of calculating the specific retention volumes of substances from their retention indices and specific retention volumes of n-alkanes

The choice of stationary phase for gas chromatography is dictated by the nature of the analytes. Polarity and selectivity are known to play an important role. This paper suggests equations for calculation of specific retention volumes of any compounds from their retention indices.     

Prediction of equivalent chain lengths from two-dimensional fatty acid retention indices

A recently introduced two-dimensional fatty acid retention index system (2D-FARI) was used as basis for prediction of equivalent chain lengths (ECL) of fatty acid methyl esters (FAME) on a BPX-70 stationary phase. Models for the relationship between 2D-FARI data and ECL values of a calibration sample with 30 common fatty acids were established by a simple multivariate regression. The models were thereafter applied on 2D-FARI data for other FAMEs and used to predict the ECLs for these compounds. The 2D-FARI values for the fatty acids in the calibration sample are given by definition. Thus, the only information necessary to calculate the ECL value for a compound run under identical conditions as the calibration sample is the 2D-FARI values for the compound, which can be acquired from literature data. The method was validated with test sets analysed with different temperature and flow programs. ECLs of various marine FAME and trans isomers of Eicosapentaenoic and Docosahexaenoic acid were predicted with root mean squared error of prediction from 0.002 to 0.012 ECL units.     

气相色谱正构烷烃和直链脂肪酸甲酯两种线性保留指数之间的转换方法

保留指数是气相色谱中用于化合物结构鉴定的重要工具。本研究对基于正构烷烃和直链脂肪酸甲酯的线性保留指数进行线性拟合,发现在所设定的4种不同的升温条件下两种保留指数之间呈现较为固定的线性关系:在弱极性柱(固定液为5%苯基和95%的甲基聚硅氧烷)和极性柱(固定液为聚乙二醇)条件下,正构烷烃保留指数(y)与脂肪酸甲酯保留指数(x)之间的关系分别为y=1.005 1x+318.51(r²=1)和y=1.036 2x+562.519(r²=1)。采用文献保留指数对所建立的线性关系进行验证,发现通过公式换算得到的保留指数均在其对应文献值的均值加减方差范围内,说明换算公式真实有效。两种保留指数之间关系的建立对于化合物结构鉴定时扩大保留指数搜索范围、减少保留指数测定实验具有重要意义。     

Why like-charged particles of dielectric materials can be attracted to one another

Calculations of surface charge density provide evidence of the physical effects responsible for particles of a dielectric material carrying the same sign of charge being attracted to one another. The results show that attraction requires a mutual polarisation of charge leading to regions of negative and positive surface density close to the point where the particles make contact. These results emphasise the significance of using charged particle models where the surface charge is non-stationary.     

Determination of average molecular polarizabilities of polycyclic aromatic hydrocarbons directly from retention indices

Summary A significant correlation has been found between the retention indices of polycyclic aromatic hydrocarbons on non-polar stationary phases and the average molecular polarizabilities of the molecules separated on these phases. Equations have been derived for the determination of the average molecular polarizabilities, directly from the retention indices.     

Kinetic analysis of the liquid-phase depolymerization of trioxane from programmed-temperature data

An experimental method for the determination of kinetic data for liquid-phase reactions under linear rise of temperature is explained for the depolymerization of trioxane. Integral kinetic analysis of the data is performed in order to determine the kinetic model and the kinetic parameters. Experiments have been carried out at different heating rates between 0.5 and 2 deg/min, leading to similar kinetic parameters. The obtained results are in agreement with the kinetic model and parameters obtained from isothermal kinetic analysis. The programmedtemperature method seems to be a useful tool for a quick determination of kinetic models, avoiding experimental work.

---

Zusammenfassung Eine experimentelle Methode zur Bestimmung der kinetischen Daten von Reaktionen in flüssiger Phase bei linearer Temperaturerhöhung wird am Beispiel der Depolymerisation von Trioxan erklärt. Eine integrale kinetische Analyse der Daten wird ausgeführt, um das kinetische Modell und die kinetischen Parameter zu ermitteln. Bei unterschiedlicher Aufheizgeschwindigkeit zwischen 0,5 und 2 K/min ausgeführte Experimente ergaben ähnliche kinetische Parameter. Die erhaltenen Ergebnisse stimmen mit dem kinetischen Modell und den kinetischen Parametern, die durch isotherme kinetische Analyse erhalten wurden, überein. Die Temperaturprogrammierung scheint eine brauchbare, experimentelle Arbeit einsparende Methode zur schnellen Bestimmung des kinetischen Modells zu sein.

---

. . , (0,5–2° .), . , . , .

     

Theoretical interpretation of the retention indices of alkylbenzenes

Summary The correlation between retention data of alkylbenzenes in GLC (measured on the stationary phase OV-101) and contribution of the Gibbs solvation energy are investigated in order to determine the dominant factor controlling retention. The retention in GLC can be predicted with help of our thermodynamic retention model.     

Calculation of retention indices in temperature-programmed gas chromatography

Summary A new method is presented for the calculation of the retention indices under linear temperature programming with or without an initial isothermal period. The data calculated by the method are in good agreement with the isothermal retention indices.     

Gas chromatographic retention indices of fentanyl and analogues

Narcotic analgesics of the fentanyl class are characterized by high potency and relatively short duration of action. These compounds nowadays have become a substitute for heroine and are highly addictive for abusers. Herein, we report retention indices of fentanyl and its eighteen analogues relative to the homologous n-alkane series. These values are determined on a moderately polar BP-5 capillary column under programmed temperature and isothermal chromatographic conditions. The analogues differ in the substituent attached to the piperidine ring nitrogen, and retention indices are found to vary according to the nature of the substituent. The effects of chromatographic conditions like temperature programming rate, carrier gas flow rate, and oven temperature are studied. Retention indices are also determined on a non-polar BP-1 column to study the influence of stationary phase polarity. Standard deviation of all the RI values is less than one index unit.