J. M. Santiuste

Solubility parameters of gas chromatographic mixed stationary phases

Gas chromatography was used to measure activity coefficients, ϒ∞, partial molar free energies of mixing, ΔG−∞1, Flory-Huggins interaction parameters, χ∞, and its enthalpic and entropic contributions, of a number of solutes on five single and fourteen mixed stationary phases at 120°C. Solubility parameters of the stationary phases, δ2, were deduced by the method of DiPaola-Baranyi and Guillet for the different solute-stationary phase combinations. The polymer-polymer interaction parameter, χ′2,3, was also calculated for the various mixed systems.

Evaluation of the effect of the cyanopropyl radical on the interaction of the methylene group with silicone stationary phases

Values of the solute-polymer interaction parameter of n-alkanes and polar substances between 90C and 200°C were obtained on two packed columns (OV-101 and OV-105). Experiments carried out with a capillary column confirmed that with non-polar solute-polymer systems the values of both the specific retention volumes and the thermodynamic parameters derived from them are equivalent to those obtained with packed columns. The results showed that n-alkanes mix better with OV-101 and polar substances are better solvents of OV- 105. The differences are small, however. Partial molar enthalpies and free energies of solution and mixing were calculated. The contribution of the methylene group of the n-alkanes to the thermodynamic parameters of solution was evaluated. The effect of cyanopropyl group substitution on the contribution of the methylene group to the partial molar free energy of solution of n-alkanes was found to be roughly linear with the cyanoalkyl group content, decreasing as the polarity of the polymer increases. The solubility parameter of the stationary phase increases only slightly when a 5% substitution of cyanopropyl groups is introduced in the polymer.

Programmed-temperature retention indices : A survey of calculation methods

Abstract Retention temperatures of various solutes were measured on an OV-105 column under different heating rates. The experimental results agree with those evaluated by means of the equation of Curvers et al. Several methods of assigning programmed temperature retention indices to each solute were tested. Comparison of the results does not allow a clear choice of any of the methods, although a procedure based on an interpolation through the use of cubic splines polynomials is preferred. The sensitivity of the various procedures towards small changes in the input data is reported.

Mixed stationary phases in gas—liquid chromatography : Partition coefficients and retention indices in OV-101-OV-25, OV-101-carbowax 20M and OV-225-SP-2340 mixtures

Abstract Partition coefficients of n-alkanes and other substances were measured at 393 K on mixed stationary phase columns prepared by mixing OV-101 with OV-25, OV-101 with Carbowax 20M and OV-225 with SP-2340. The results are examined with respect to the Purnell—Vargas de Andrade and Perry—Tiley relationships. The solvent—solvent interaction parameter was calculated in the three systems. When the value of this parameter is higher than 2 a clear departure from the linear approximation was observed. Retention indices were also calculated and compared with those predicted by the above relationships.

Temperature effect on the characteristic solute-solvent retention interactions, calculated with Abraham's solvation model, for 16 GLC stationary phases

Abstract Specific stationary phase constants used in Abrahams solvation model were determined by multiple linear regression analysis (MLRA) for 16 stationary phases (SP) at various temperatures. Hydrogen-bond acidity complexes were negligible for all SPs. The influence of temperature on the solute–SP interactions and on its different terms, both nonpolar (or cavity-dispersion), and polar, has been determined for a series of solutes. Good negative-slope straight lines both for the cavity-dispersion vs. T and for the polar contribution vs. T plots were obtained, the former having a much greater slope than the latter. Also, the dependence of the cavity-dispersion and of the polar retention terms for various chemical functions in three SPs at different temperatures was studied. The cavity-dispersion term increased with decreasing temperature, while the polar term was almost temperature independent. At each temperature, the cavity-dispersion term increased with the Z chain length, excellent linear correlations being obtained for every chemical function tested.

Programmed-temperature gas chromatography: Comparative study of retention temperatures on four unequally polar stationary phases

Abstract Retention temperatures ( T R ) of a series of solutes on four packec columns coated with OV-105, PS-255, di- n -decyl phthalate and OV-275 were measured at different programming rates and compared with other T R values calculated by some current equations, confirming that the equations of Curvers et al. , Krupcik et al. and Akporhonor et al. predict the retention temperatures closest to the observed T R values. Programmed-temperature retention indices (PTRIs) calculated by cubic splines interpolation of both the experimental and some other calculated T R values were also compared, taking the former as standard, the resulting PTRI values differing by only 2% for at least 90% of the solutes on the low-polarity stationary phases.

Cubic splines compared with other methods for the calculation of programmed temperature retention indices

SummaryProgram temperature retention indices for fifteen nonalkane solutes have been determined by cubic splines, by other procedures found in the literature and by interpolation of the n-alkanes retention time logarithm for eleven temperature programs. A comparison in terms of variance of the differences between PTRI calculated by CS and each of the remaining methods is made for each of the eleven program runs, for each of the three stationary phases used and for many of the programs. The smallest variances obtained result when the Zenkevich, van den Dool & Kratz and Chen et al. methods are tested. The stationary phase polarity is of no relevance since it has no effect on the specific PTRI found by the different methods employed in this work.

Method for the classification and selection of stationary phases in gas chromatography

Abstract A new method of classification is applied to 233 stationary phases used in gas chromatography. Clustering together all those which have similar chromatographic behaviour, 45 are found to be singular in the sense that no other stationary phase exhibits similar characteristics and therefore they may not be replaced by any other. The remaining 188 stationary phases may be reduced to 33 selected liquids which may represent the larger set of 188, in the sense that all selectivity possibilities of the 188 stationary phases are retained in the 33 selected. A further reduction in the number of selected stationary phases will adversely affect the separation capacity of the set. The selected list of 33 stationary phases is not unique, and many of them may be replaced by an equivalent one without any loss in separation capacity.

Molecular structural coefficients of Takács. Their dependence on column temperature, stationary phase polarity and solute chemical nature

SummaryMolecular structural coefficients, Sc, for one hundred solutes have been calculated by means of the Takács equation using retention data obtained with over fifty stationary phases, SP. Employing data of seven SPs (characterized in our laboratories) it was found that the variation of Sc with column temperature was linear for most solutes. With data of n-decane and the ten McReynolds probes on up to fifty SPs of polarity less than RP=72, at 120°C, it was found that the Sc of n-decane and cis-hydrindane decreased slightly with increasing SP polarity, while the Sc of non-alkanes remained constant or increased very little as the SP polarity increased. The points for n-decane fit well to a second order polynomial. Again using a temperature of 120°C, the increments of Sc for solutes belonging to an homologous series were correlated with the polarity of SPs. Reasonably straight lines were obtained for all the chemical functions studied, Sc increasing with increasing SP polarity.

Calculation of programmed temperature retention indices: Part 2: Optimization of temperature dependence calculation

SummaryProgrammed Temperature Retention Indices (PTRI) of several solutes on four packed columns coated with stationary phases covering a range of polarities have been estimated for sixteen temperature programs by exploiting isothermal retention data obtained at 70–180°C. PTRI calculations have been carried out by interpolating the retention temperatures calculated according to Curvers et al. from the graphs of retention index against column temperature, matched according to polynomials of grade 1 to 3 and by hyperbolic fitting. PTRIs by the van den Doole & Kratz equation and by cubic splines have also been computed. Comparison is made of these PTRIs with those calculated from cubic splines of the measured retention temperatures throughout the various temperature programs and the retention index deviations in terms of variance and relative error are explored. The smallest variance are found for the less polar stationary phases, PS-255 and OV-105; the biggest variance values are found for OV-275. Data are given showing that about 95% of the determinations of PTRIs on the low polarity stationary phases show deviations of not greater than 2%.