Kováts' coefficients for predicting polarities in silicone stationary phases and their mixtures

Summary A correlation between the retention polarity and the Kováts' coefficient has been found for a number of commercial stationary phases used in gas chromatography. The correlation has been used to predict the polarity of a few mixed stationary phase columns prepared as binary mixtures of OV-101 with OV-25, DC-550 or Carbowax 20M, and also mixtures of OV-225 with SP-2340. A linear relationship was found between polarity and mixture composition. The temperature dependence of the Kováts' coefficient was investigated and found to increase linearly with temperature, the rate of increase depending on the polarity of the stationary phase, with greater increases for more polar stationary phases.     

74% Slope efficiency from a diode-pumped Yb3+:LiNbO3:MgO laser crystal

An optimization of the laser action performance from a diode-pumped Yb³⁺-doped LiNbO₃:MgO crystal has been carried out. In this sense, efficient laser action at 1.06 m when pumping with a fiber-coupled laser diode at 980 nm has been demonstrated, achieving laser slope efficiencies as high as 74%. The influence of output mirror transmittance on both pumping threshold and laser slope efficiency has been investigated, and the parameters of relevance in laser dynamics (emission cross section and optical losses) have been determined. Under the experimental conditions leading to maximum slope efficiency, the pump power at threshold was 300mW, and the pump-to-laser conversion efficiency was 40%. PACS 42.55.Xi; 42.55.Rz; 42.60.Lh     

Factors Influencing the Isothermal Retention Indices of 51 Solutes on 12 Stationary Phases of Different Polarity: Applicability of the Solvation Parameter Model

Isothermal retention indices (I) at 333–413 K on 12 stationary phases (SPs) covering a wide polarity range of a variety of volatile solutes belonging to 7 one-heteroatom chemical function series and 10 non-series solutes have been determined. The I values were computed with a method (LQG method) which does not require the determination of holdup times of the chromatographic column. I values of some compounds never before studied are reported. The influence on the retention indices of the column temperature, methylene number, and polarity of both the stationary phase and the solute has been studied. The solvation parameter model (SPM) as a function of I has been used for predicting I values, and for unraveling the influence of the polarity of stationary phase and solute on the retention indices. Seeley et al.’s formulation of the SPM has been used for quantifying the influence of polar and non-polar interactions on the I, and for checking the agreement between calculated and experimental values. According to our results, the I values obtained by the modified SPM can be considered equal to the experimental I values at the 99 % confidence level.

     

Contribution to linearly programmed temperature gas chromatography. Further application of the Van den Dool-Kratz equation, and a new utilization of the Sadtler retention index library

Programmed temperature retention indices (PTRIs) calculated according to the equations of Van den Dool and Kratz, Golovnya and Uraletz, and Erdey et al. (also referred to as Antoine's integrated equation) are used in this work. Precalculation of isotherm retention indices from the results of a linearly programmed temperature GC is also presented. Deviations between experimental and calculated isothermal retention indices are below 2 retention index units. A relative "volatility" retention index is defined, as a function of the "volatilities"of the solute and the bracket reference n-alkanes. The comparison of the "volatility" retention indices with the PTRIs obtained with the other above equations shows absolute deviations of up to 4 retention index units. Based on an earlier "equivalent" temperature concept and on Tekler's proviso, a novel way for the utilization of Sadtler's retention index database, which takes advantage of the 3 data supplied by the library, is proposed.     

Energetics and structural properties, in the gas phase, of trans-hydroxycinnamic acids

We have studied the energetics and structural properties of trans-cinnamic acid (CA), o-, m-, and p-coumaric acids (2-, 3-, and 4-hydroxycinnamic acids), caffeic acid (3,4-dihydroxycinnamic acid), ferulic acid (4-hydroxy-3-methoxycinnamic acid), iso-ferulic acid (3-hydroxy-4-methoxycinnamic acid), and sinapic acid (3,5-dimethoxy-4-hydroxycinnamic acid). The experimental values of Δ(f)H(m)°(g), determined (in kJ·mol(-1)) for CA (-229.8 ± 1.9), p-coumaric acid (-408.0 ± 4.4), caffeic acid (-580.0 ± 5.9), and ferulic acid (-566.4 ± 5.7), allowed us to derive Δ(f)H(m)°(g) of o-coumaric acid (-405.6 ± 4.4), m-coumaric acid (-406.4 ± 4.4), iso-ferulic acid (-565.2 ± 5.7), and sinapic acid (-698.8 ± 4.1). From these values and by use of isodesmic/homodesmotic reactions, we studied the energetic effects of π-donor substituents (-OH and -OCH(3)) in cinnamic acid derivatives and in the respective benzene analogues. Our results indicate that the interaction between -OCH(3) and/or -OH groups in hydroxycinnamic acids takes place without significant influence of the propenoic fragment.     

Prediction of specific retention volumes in gas chromatography by using Kováts and molecular structural coefficients

The Kováts coefficients, K_c,Z, of a stationary phase and the solute's molecular structural coefficients, S_c,i, depend both on the specific retention volume V_g, of a solute or homologous series and on the “log-plot” slope, b, of a chromatographic column. In view of this dependence, the feasibility of predicting V_g in three instances was investigated: (a) V_g prediction of any n-alkane from K_c,Z and retention data of n-decane; (b) V_g prediction of any solute from the temperature dependence of the above parameters and (c) V_g prediction of any term of a homologous series from the correlations of the S_c increments, ΔS_c, with the organic structural function. The possibilities of the method are evaluated in the light of the analysis of the deviations of the predicted V_g values from the measured values.     

Retention Indices of 55 Solutes Belonging to Eight Monofunctional Groups Homologous Series on 14 Chromatographic Capillary Columns

Retention indices, RI, of 55 solutes belonging to eight chemical monofunctional group series were computed at 373 K from retention factors measurements on 14 capillary columns coated with stationary phases, SP, spanning almost the whole polarity range. RI-values of some of these analytes were validated by comparison with literature values. Positive slope straight lines were obtained for the isothermal RI versus Z plots for the eight chemical functions. For a given series the slope (A) is rather insensitive to RP, while the intercept (FF) clearly increases linearly with increasing RP. For a given stationary phase A does not show any clear trend with increasing solute polarity, while FF increases clearly from the less polar to the most polar series.     

Prediction of the Retention Indices of Benzene and Methylbenzenes Based on their Retention Data-Physico Chemical Properties Relationship

Retention indices of benzene and 12 methylbenzenes were determined on two capillary columns coated with HP-5 and ZB-WAX at 100 °C. Comparison with the retention indices published by other researchers yields a good accordance. The relationship between the retention index values and several physico-chemical properties of these solutes (freezing point, boiling point, molar volume, van der Waals volume, molar refraction, refraction index, connectivity index, dipole moment and vapor pressure) was investigated by multiple linear regression analysis (MLRA). MLRA equations of seven and eight variables predicted retention indices with mean deviations of 0.66–0.97 index-units in squalane and Carbowax 20 M, and 0.76–1.25 index-units in HP-5 and ZB-WAX. PCA was applied to the system of solutes retention data and stationary phases used, giving results consistent with those of MLR analysis. Samples are scattered or joined by curves. An arrangement of the stationary phases according to the polarity is observed. TCEP was one outlier since it is much more polar than any others.Two groups of variables can be envisaged, one of which is close to the origin of the coordinates, the physicochemical properties that depend linearly. Solute vapor pressure and molar volumes were outliers.