Ján Krupčík

Determination of the interconversion energy barrier of enantiomers by separation methods.

Separation methods have become versatile tools for the determination of kinetic activation parameters and energy barriers to interconversion of isomers and enantiomers in the last 20 years. New computer-aided evaluation systems allow the on-line determination of these data after separating minute amount of pure compounds or mixture of isomers or enantiomers, respectively. Both dynamic interconversion during the separation process as well as static stopped-flow techniques have been applied to determine the kinetic activation parameters and interconversion energy barriers by separation methods. The use of (1) combinations of batchwise kinetic studies with enantioselective separations, (2) a continuous flow model, (3) a comparison of real chromatograms with simulated ones, (4) stopped-flow techniques, (5) stochastic methods, (6) approximation functions and (7) deconvolution methods, for the determination of interconversion energy barriers by separation methods is summarized in detail.

Gas chromatography of all C15C18 linear alkenes on capillary columns with very high resolution power

Abstract Conditions were studied for the separation of mixtures of all the 60 isomers of C 15 C 18 n -alkenes in the presence of the corresponding n -alkanes in highly efficient glass capillary columns ( N ≈ 0.5·10 6 effective plates for n -alkenes with k ≈ 3), coated with C 87 hydrocarbon, Apiezon L or Carbowax 20M as stationary phase. The separation of cis - and trans -isomers of n -alkenes is made possible at a sufficiently high column efficiency by the different dependences of their retentions on temperature. The separation of positional isomers of n -alkenes having even carbon numbers for the pairs with the most centrally situated double bonds can be achieved only by use of highly efficient columns with polar or non-polar stationary phases ( n req ≈ 10 6 plates). Correlations between the structure and increments H , δ I , d I /d T and Δ I , derived from retention indices of n -alkenes, were used for identification as they reflect the position of the double bond, the geometrical arrangement and the length of the carbon chain in various isomers. The so-called propyl effect was confirmed for trans -4-alkenes, disturbing the regularity of all correlations between structure and retention. The influence of adsorption of n -alkanes and n -alkenes at the polar phase-carrier gas interface on the retention characteristics is discussed. Reproducibility of retention indices of n -alkene isomers is a function of their capacity ratios (thickness of the stationary phase film in the column), decreases with polarity of the stationary phase and the isomer under analysis and with the difference between a reference standard and the n -alken ein question. These effects are so significant for the columns with Carbowax 20M that a different retention sequence was found for some n -alkene isomers in columns with relatively small differences in the thickness of the stationary phase.

Use of a polar ionic liquid as second column for the comprehensive two-dimensional GC separation of PCBs.

The orthogonality of three columns coupled in two series was studied for the congener specific comprehensive two-dimensional GC separation of polychlorinated biphenyls (PCBs). A non-polar capillary column coated with poly(5%-phenyl-95%-methyl)siloxane was used as the first ((1)D) column in both series. A polar capillary column coated with 70% cyanopropyl-polysilphenylene-siloxane or a capillary column coated with the ionic liquid 1,12-di(tripropylphosphonium)dodecane bis(trifluoromethane-sulfonyl)imide were used as the second ((2)D) columns. Nine multi-congener standard PCB solutions containing subsets of all native 209 PCBs, a mixture of 209 PCBs as well as Aroclor 1242 and 1260 formulations were used to study the orthogonality of both column series. Retention times of the corresponding PCB congeners on (1)D and (2)D columns were used to construct retention time dependences (apex plots) for assessing orthogonality of both columns coupled in series. For a visual assessment of the peak density of PCBs congeners on a retention plane, 2D images were compared. The degree of orthogonality of both column series was, along the visual assessment of distribution of PCBs on the retention plane, evaluated also by Pearsons correlation coefficient, which was found by correlation of retention times t(R,i,2D) and t(R,i,1D) of corresponding PCB congeners on both column series. It was demonstrated that the apolar+ionic liquid column series is almost orthogonal both for the 2D separation of PCBs present in Aroclor 1242 and 1260 formulations as well as for the separation of all of 209 PCBs. All toxic, dioxin-like PCBs, with the exception of PCB 118 that overlaps with PCB 106, were resolved by the apolar/ionic liquid series while on the apolar/polar column series three toxic PCBs overlapped (105+127, 81+148 and 118+106).

Comparison of sorbents for solid-phase extraction of polar compounds from water

Abstract Octadecyl-bonded silica, styrene—divinylbenzene and hydroxyethyl methacrylate—ethylene dimethacrylate sorbents were tested for their ability to preconcentrate aniline, benzothiazole, cyclohexanone and cyclohexanol. Breakthrough curves for these compounds were measured for aqueous solutions at pH 5.8 and 10.0 by gas chromatographic analysis of fractions of the aqueous effluents. Elution curves of the analytes in methanolic eluates were obtained in order to determine the optimum volume of the eluate. Using breakthrough volumes and widths of the elution curves, theoretical preconcentration factors were calculated for all analyte—aqueous sample—sorbent systems tested. Octadecyl-bonded silica and styrene—divinylbenzene sorbents were found to be suitable for the preconcentration of weakly polar to polar compounds for practical water quality control purposes.

Gas chromatographic separation fo some dialkyldithiocarbamates of nickel(II)

Abstract The possibility of separating some nickel(II) bis0dialkyldithiocarbamates) by gas chromatography in a packed column with SE-30 as the stationary phase has been studied. In order to prove the structure of nickel(II) bis(N,N-diethyldithiocarbamate) in the gaseous phase, its mass spectrum is presented. The thermal behaviour of nickel(II) bis(dialkyldithiocarbamates) was studied by means of thermal analysis. It was found that it is possible to apply gas chromatography to compounds that are solids at the temperature of separation. The peaks of nickel(II) bis(dialkyldithiocarbamates) are symmetrical and their shape does not differ from those of hydrocarbons chromatographed under similar conditions.

Correlation of the boiling points of non-branched C9 and C10 olefins with the gas chromatographic retention indices

Abstract A correlation was made between the boiling points of fourteen non-branched nonenes and decenes and the retention indices, and also a comparison of the results obtained by known methods of calculation with the available tabulated data. The gas chromatographic measurements were carried out on a 200-m long capillary column (stainless steel) coated with squalane at 86, 100 and 115° and permitted boiling points to be determined with a reproducibility of ± 0.1°. Substantial deviations were found from the Kovats rule δI ≈ kp δTb for the behaviour of isomeric hydrocarbons on a non-polar stationary phase. In the case of the olefins studied, the proportionality constant, for which a value of approximately 5 is stated in the literature, fell within the range 1.8–13.9 on squalane. The correction factor fc used for the calculation of IB by M atukuma is constant only in the case of trans-alkenes, whereas for cis-alkenes and I -alkenes it is dependent on the number of carbon atoms in the olefin molecule.

Flow-modulated comprehensive two-dimensional gas chromatography with simultaneous flame ionization and quadrupole mass spectrometric detection.

Flow-modulated comprehensive two-dimensional gas chromatography with simultaneous monitoring of the separation by flame ionization (GC × GC-FID) and quadrupole mass spectrometric (GC × GC-qMSD) detection was studied for the analysis of gasoline and kerosene samples. The acquisition frequency of the FID was 100 Hz and of the qMSD 18 Hz for the mass range m/z 40-300. The instrumental set-up is such that both one-dimensional (GC-FID and GC-qMSD) and two-dimensional separations using the same working conditions can be performed. Gasoline and kerosene samples were analyzed on the column combination HP-5MS ((1)D)+HP INNOWax ((2)D). Three modulated peaks were obtained for each hydrocarbon present above 0.1% with ca. 300 ms peak width at the base using 6 s modulation times. Modulated peaks in GC × GC-FID were thus characterized by ca. 30 points while those in GC × GC-qMSD method by 6-8 points only. The FID speed is sufficient for reliable quantitative analysis, while the qMSD scan speed is perfectly appropriate for identification purposes. Moreover, in the GC × GC-qMSD method considerably improved quality of uncorrected spectra was obtained, arising from the enhanced separation over one-dimensional GC-MSD analysis. Spectral match qualities of up to 98% were found.

On the use of ionic liquid capillary columns for analysis of aromatic hydrocarbons in low-boiling petrochemical products by one-dimensional and comprehensive two-dimensional gas chromatography.

One-dimensional and comprehensive two-dimensional flow modulated gas chromatography with simultaneous flame ionization and mass spectrometric detection were applied for the identification and quantification of benzene, toluene, ethyl benzene and xylenes (BTEX) as well as of all C9-C11 aromatic hydrocarbons in the low-boiling petroleum products gasoline, reformate and fluid catalytic cracking (FCC) samples. GC×GC experiments were performed on two reversed phase polarity column sets namely SLB-IL100 (25m×250μm i.d.×0.2μm df)+HP-5MS (5m×250μm i.d.×0.25μm df) and SLB-IL111 (30m×250μm i.d.×0.2μm df)+HP-5MS (5m×250μm i.d.×0.25μm df). The one-dimensional GC experiments were carried out on the same ionic liquid columns. The most powerful method is GC×GC on the SLB-111+HP-5MS column combination. Quantitative analysis of individual aromatic hydrocarbons (C6-C11) present in gasoline, reformate and fluid catalytic cracking (FCC) samples was performed by GC×GC-FID using the internal normalization method. Mass spectra obtained by GC×GC-qMSD were used for identification of the aromatic hydrocarbons in these samples.

Hochleistungs-gaschromatograpahie an flüssigkristallglaskapillaren☆

Abstract High-performance glass capillary columns with 5- n -heptyl-2-(4- n -nonyloxyphenyl)-pyrimidine were applied for separations of isomeric alkylbenzenes and n -alkens in smectic C and smectic A also in the nematic, isotropic and crystalline range. Structure-retentio correlations were discussed from calculated retention indices and their dependence on temperature. The smectic modifications shows better separations in comparison with previous methods.

Gas chromatography of 209 polychlorinated biphenyl congeners on an extremely efficient nonselective capillary column.

The gas chromatographic-mass spectrometric (GC-MS) separation of all 209 polychlorinated biphenyl (PCB) congeners was studied on an extremely efficient 80 m x 0.1mm i.d. capillary column coated with a 0.1 microm film of poly(5%-phenyl methyl)siloxane stationary phase. The quality of the separation and the number of resolved and coeluting peaks were compared to predictions according to the statistical overlap theory (SOT) and to literature data on PCB separations obtained by one-dimensional and comprehensive two-dimensional GC (GC x GC) and GC-MS. Mass spectral and chemometric deconvolution procedures were used to resolve overlapping peaks. On the highly efficient column, 195 PCB congeners were resolved in 96 min separation time using spectral and chemometric deconvolution. This number is comparable to the best separations described in GC x GC-MS mode. The novel method was developed for spectral deconvolution of overlapped PCB congeners which was verified determining the most toxic, dioxin-like PCBs both in the model mixture of 209 PCBs as well as in the Aroclor 1242 and Aroclor 1254 formulations.