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1
Content available remote Could molar heat capacity be derived from chromatographic data?
Ciążyńska-Halarewicz K., Kowalska T.
Acta Chromatographica
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2006
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No. 16
119-139
EN
This paper, the latest in an established series on the alternative use of gas chromatographic data, is devoted to a possibility of deriving yet ano-ther thermodynamic magnitude from these data, the molar heat capacity, Cp. Traditionally, the molar heat capacity of a substance can be obtained directly by use of calorimeter [1]. Occasionally, however (e.g. when suffi-cient material is not available), this method can prove quite complicated. The question has thus been asked whether there are alternative possibilities of indirect measurement of this particular magnitude. In the work discussed in this paper we undertook this challenge by making an attempt to deter-mine molar heat capacities for the three classes of compound, alkylbenze-nes, aldehydes, and ketones, from simple chromatographic data originating from the capillary gas chromatography (CGC) and a set of specially devised mathematical models, complemented with appropriate statistical procedu-res.
2
Content available remote Calorimetry compared with gas chromatography: are comparable molar heat capacities obtained by use of these two approaches?
Ciążyńska-Halarewicz K., Korzenecki P., Helbin M., Kowalska T.
Acta Chromatographica
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2006
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No. 17
72-96
EN
In this study molar heat capacities (Cp) were determined for aliphatic alcohols by using simple gas chromatographic data and mathematical models correctly derived from the laws and rules of physical chemistry and chromatography. The results obtained were compared with those derived by direct calorimetric measurement and with data calculated by use of the Kopp and Neumann rule. In this way an attempt was made to answer the question posed in the title of this paper–is the accuracy of the non-standard approach (even, if computationally rather complicated) comparable with that of the traditional measurement technique? From the results obtained it is clearly apparent that the results obtained by use of our novel approach are comparable with those originating from the other measurement and computational approaches. This paper is the latest in a series devoted to alternative methods for derivation of thermodynamic data from gas chromatographic results.
3
Content available remote Relative retention or non-reduced relative retention? Which is better suited for prediction of the molar enthalpy of vaporization?
Ciążyńska-Halarewicz K., Kowalska T.
Acta Chromatographica
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2005
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No. 15
97-118
EN
Continuing the cycle of investigations introduced in earlier publications [1–9], in this article we present further applications of capillary gas chromatography to predicting selected thermodynamic data of analytes. We derived two novel mathematical models which couple the chromatographic property, i.e. the relative retention, r, with physicochemical properties, i.e. the boiling point of the analyte, TB, and – depending on the relationship – either the molar volume, Vm, or the molar refraction, Rm. These two non-empirical models assume the general form: r=Aexp(BX + C X/TB) where X = Vm or Rm, and A, B, and C denote physicochemically relevant equation fitting constants. Constants B and C enable calculation of the ther-modynamic property, i.e. the molar enthalpy of vaporization, ΔHvap, for the analytes studied. These equations were tested for three groups of analytes of different polarity (alkylbenzenes, aldehydes, and ketones). The empiri-cal chromatographic data were collected in isothermal mode with three capillary columns coated with low- and the medium-polarity stationary phases at five different temperatures ranging from 323 to 423K. After sta-tistical data processing, derived numerical values of the molar enthalpy of vaporization were compared with data taken from the literature to test the fitting and the predictive performance of the novel non-empirical models..
4
Content available remote Mathematical models of solute retention in gas chromatography as sources of thermodynamic data. Part II. Aldehydes as the test analytes
Ciążyńska-Halarewicz K., Kowalska T.
Acta Chromatographica
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2003
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No. 13
81-94
EN
Direct determination of thermodynamic data has always been a complicated and troublesome experimental task; gas chromatography is among long-established working tools well suited to performing this particu-lar task indirectly [1-11]. This paper is the next step in research introduced in other publications [12,13]. Eight different mathematical models (coupling gas chromatographic retention data of analytes with their physicochemical properties) were used to determine the molar heat of vaporization, ΔHvap, and the chemical potential for partitioning of one methylene group between the two phases of the chromatographic system, Δμp(CH2), for consecutive members of a group of analytes, this time the aldehydes. The experiment was performed on low- and medium-polarity stationary phases in the temperature range 323 to 423 K.
5
Content available remote A study of the dependence of the Kováts retention index on the temperature of analysis on stationary phases of different polarity
Ciążyńska-Halarewicz K., Kowalska T.
Acta Chromatographica
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2003
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No. 13
69-80
EN
The dependence of Kováts retention indices on the temperature of GC analysis is not always regular. In some chromatographic systems this dependence is characterized by a readily perceptible minimum [1-3]. To monitor this type of relationship a set of test compounds was selected from among the aldehydes, ketones, and alkylbenzenes and their gas chromato-graphic behaviour was studied on stationary phases of different polarity and over a wide range of working temperatures. For some systems we observed a minimum on the plot of I against Tc. This minimum was not only observed, it was also computationally confirmed by use of the equation I = A + B/Tc + ClnTc, where A, B, and C are terms of the equation with physicochemical significance [2,4 - 6]. On the basis of this equation we were also able to evaluate two thermodynamic magnitudes, the activation enthalpy, ΔH±, and the chemical potential of the partitioning of one methylene group between the two phases of the chromatographic system, μp(CH2), for all the analytes investigated.
6
Content available remote Thermodynamic relationships between retention, boiling point, and molar volume and between retention, boiling point, and molar refraction for the homologous series methyl n-alkyl ketones in CGC
Ciążyńska-Halarewicz K., Borucka E., Kowalska T.
Acta Chromatographica
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2002
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No. 12
49-64
EN
We propose two thermodynamic relationships which couple analyte retention with selected physicochemical properties - exponential dependence of analyte relative retention times (τ) on boiling points (TB) and molar volume (Vm) or, alternatively, on boiling points and molar refraction (Rm). The statistical performance of these retention models was tested on experimental data obtained for homologous analytes (methyl n-alkyl ketones) by use of isothermal capillary gas chromatography (CGC) on stationary phases of different polarity. Computations were performed by use of Statistica 5.0 PL software. The same models were then used to predict the thermodynamic properties selected (i.e. the molar enthalpies of vaporization of the analytes employed) and their physicochemical performance was evaluated by comparison of the results obtained with those obtained from the literature. The experiments and computations performed led to the conclusion that the models introduced enable prediction of analyte retention and that they can also prove useful for extraction of thermodynamic information from the CGC results.
7
Content available remote Temperature dependence of Kováts indices in gas chromatography. Statistical and thermodynamic verification of a "kinetic" model
Ciążyńska-Halarewicz K., Borucka E., Kowalska T.
Acta Chromatographica
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2002
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No. 12
65-79
EN
In this paper we present a new model of describing the temperature-dependence of Kováts retention indices. It is regarded as a "kinetic" model, because it uses certain elements of chemical kinetics (e.g. the enthalpy and entropy of activation, ΔH≠ and ΔS≠) for thermodynamic description of retention processes in gas chromatography. It was founded on the transition-state theory (TST) and involves the Eyring equation. Mathematically it can be considered as an extended Antoine-type equation, although it surpasses that relationship owing to its greater flexibility and hence its better fitting of experimental results. It also anticipates the physical minima which occasionally occur when retention indices are plotted against the measure-ment temperature.
8
Content available remote Application of selected topological indices to prediction of the retention times of methyl n-alkyl ketones in gas chromatography
Ciążyńska-Halarewicz K.
Acta Chromatographica
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2000
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No. 10
56-75
EN
The retention times of members of a homologous series of methyl n-alkyl ketones have been measured isothermally, at four different tempe-ratures, by capillary gas chromatography on the low-polarity stationary phase. The results obtained were compared with those calculated by use of one- and two-parameter linear correlation equations expressing the dependence of retention on selected topological indices. The performance of the topological indices selected for prediction of retention times under the conditions used was scrutinized. An inconsistency in the separation data within the investigated homologous series (vis, a split of the data into individual sub-series) was observed.
9
Content available remote Chromatographic evaluation of the dehalogenation of chlorobenzene in aqueous solutions
Ciążyńska-Halarewicz K.
Acta Chromatographica
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1998
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No. 8
144-153
EN
Investigation of the dehalogenation of organic compounds has undisputed theoretical [1] and practical [2] importance. This paper reports a study of the kinetics for the dehalogenation of chlorobenzene in aqueous solutions, and their dependence on reaction time and temperature, catalyst concentration and system pH. Quantitative analysis was performed by capillary gas chromatography with an external standard.
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