Room temperature ionic liquids (RTIL) are organic salts composed of an organic cation and organic or inorganic anion, with a melting point below room temperature. They have been used as novel solvent systems in organic synthesis, solvents immiscible with water and polar solvents in liquid-liquid extraction, new background electrolytes for voltammetric studies and batteries, non-volatile matrices for MALDI-MS, stationary phases in gas chromatography and mobile phases in HPLC. In this study, RTILs were used as stationary phases in capillary gas chromatography. Kovats retention indexes of model mixtures of hydroformylating products of undec-1-ene, dodec-1-ene and tridec-1-ene, were measured. The measured data were confronted with those on classical (commercial) nonpolar column HP-5 (5% poly(diphenylsiloxane) 95% poly(dimethyl-siloxane)) and polar column SP-2340 (100% poly[bis(3-cyanopropyl)siloxane]).

The optimisation of the selectivity of two columns coupled in series has been investigated in HPLC. Two columns with different polarities (PEG and CN) were coupled in series via a T connector and the retention of analytes chromatographed on the column system was tuned by varying the individual mobile phase flows in the coupled columns. The flow rate ratio necessary for receiving an optimum selectivity was calculated on the basis of the measured retention factors on the individual columns. The performance of this method has been studied by the separation of a model mixture of 17 analytes with various functionalities.

Gas chromatographic separation of enantiomers of C-4-C-8 secondary alcohols and n-pentyl secondary alkyl ethers has been studied using capillary columns with the following stationary phases: heptakis(6-O-tert-butyldimethylsilyi-2,3-di-O-acetyl)-beta-cyclodextrin (6-TBDMS-2,3-DA-beta-CD), permethyl-beta-cyclodextrin (ChirasilDex), heptakis-(2,6-di-O-methyl-3-beta-petityl)-beta-cyclodextrin (2,6-diMe-3-Pe-beta-CD), and octakis-(2,6-di-O-methyl-3-O-pentyl)-gamma-cyclodextrin (2,6-diMe-3-Pc-gamma-CD). On the 6-TBDMS-2,3-DA-beta-CD support enantiomers of secondary alcohols were successfully separated, contrary to n-pentyl secondary alkyl ethers. In turn, the latter were successfully separated on 2,6-diMe-3-Pe-beta-CD and 2,6-diMe-3-Pe-gamma-CD columns, oppositely to the corresponding secondary alcohols. Different enantioselectivitics of polar and non-polar cyclodextrin stationary phases were discussed in the light of various contributions of polar and non-polar interactions to the separation phenomena.

A novel on-flow gas chromatographic (GC) method is developed for the determination of the kinetic rate constants and interconversion energy barrier of thermally labile enantiomers. The validity of the developed method is approved by the study of interconversion of 1-chloro-2,2-dimethylaziridine enantiomers on an achiral column. The overall experiments are performed in a series of three columns placed in two independently heated GC ovens. The racemate of the 1-chloro-2,2-dimethylaziridine is injected and separated in the first chiral column at 60 degrees C in which the interconversion of enantiomers is suppressed. Separated enantiomers are then transferred into the achiral column, where the enantiomers are interconverted at a selected temperature under the current carrier gas flow. Effluent from this column is transferred into the second chiral column, where the native enantiomers and those originated by the on-flow interconversion on an achiral column are again separated at 60 degrees C. Chromatograms obtained by monitoring the effluents from the second chiral column are used to determine the peak areas of the original and the newly interconverted enantiomers. The corresponding peak areas and the interconversion times are used to calculate the interconversion rate constants and energy barriers of the 1-chloro-2,2-dimethylaziridine enantiomers. The apparent energy barriers of the enantiomers of 1-chloro-2,2-dimethylaziridine are equal for both enantiomers within a 95% confidence interval and independent of the polarity of the stationary phase of the column in which the interconversion of enantiomers occur.

The gas chromatographic separation of enantiomers of seven N-TFA-O-alkyl amino acid derivatives was studied on four different permethyl- and 2,6-di-O-methyl-3-O-pentyl-beta- and -gamma-CD stationary phases. It was shown that the separation of enantiomers N-TFA-O-alkyl amino acid derivatives depends both on the length of the linear alkyl chain attached to the stereogenic carbon (R-1) and to the ester part of the amino acid derivative (R-2). The cyclodextrin cavity size also affected selectivity. The separation of the amino acid derivatives decreases with increasing length of both the R, and R-2 alkyl chains on beta-CD stationary phases, but improves on gamma-CD stationary phases. The separation of enantiomers of all N-TFA-O-methyl amino acid esters, is better on the larger gamma-cyclodextrin CSPs except for enantiomers of N-TFA-O-alkyl esters of alanine which are better separated on beta-CD stationary phases.

The enantioselective tuning of two columns coupled in series is investigated in chiral high-resolution gas chromatography. Two columns with opposite enantioselectivities (Chirasil-L-Val and Chirasil-D-Val) are coupled in series via a T connector, and the relative retention of enantiomers chromatographed on the system is changed by varying the individual carrier gas flow rates in the coupled columns. The flow-rate ratio necessary for the required selectivity is calculated on the basis of the measured retention factors on the individual columns. The performance of this method for adjusting selectivity is studied by the separation of enantiomers of the N-TFA-O-methyl esters of six amino acids. It is demonstrated that the change of the coupling point carrier gas pressure, at the constant inlet and outlet pressures, may change the enantioselectivity of the given column series to such an extent that the enantiomer elution order may be reversed.

The results of analysis of high-boiling petroleum fractions by classic capillary gas chromatography with flame ionization detector (CGC-FID) were compared with those obtained in short capillary columns under conditions of fast capillary gas chromatography, For the determination of the high-boiling fractions by CGC-FID, both the calibration curve and its combination with internal standard were proposed. It was confirmed that light gas oil call be used as an internal standard for the analysis of high-boiling petroleum fractions in environmental samples, Both the classic capillary gas chromatography and its modified fast version give comparable results in spite of a significant drop in the column efficiency at the last stage.

The CGC-FID determination of petroleum hydrocarbons in environmental samples is based on the assumption that the mass response of FID for hydrocarbons is constant and any petroleum distillation fraction can be used as a reference mixture for calibration purposes. It has been shown that the mass responses of FID for higher bailing hydrocarbons are not constant. Moreover, it was found that mess response calibration factors for petroleum oils boiling within an equal temperature interval differ more than 2.5 fold in dependence on the hydrocarbon group composition. In the CGC-FID determination of such petroleum hydrocarbons in environmental samples it is therefore necessary to use a reference material which provides not only chromatograms but also the group composition.

The retention behavior of N-trifluoroacetyl-O-alkyl esters of selected amino acids with various types of alkyls in ester group was studied by capillary gas chromatography with modified cyclodextrin stationary phases. A model set of six different esters of five amino acids was analyzed on two columns coated with permethyl-beta-cyclodextrin bonded to polysiloxane elastomer (ChirasilDex), and heptakis (6-O-tert-butyldimethylsilyl-2,3-di-O-acetyl)-beta-cyclodextrin dissolved in OV 1701 in a 1:1 ratio. It was found that the variation of enantiomeric separation with temperature and elution sequence of enantiomers depends on the nature of alkyl groups bonded both to asymmetric carbon atom and in ester group. A temperature dependent inversion of elusion sequence was observed for N-TFA-O-n-butyl valine derivative on ChirasilDex column. (C) 1996 John Wiley & Sons, Inc.

Gas chromatographic study on chiral separation of PCBs was performed in a series of capillary columns coated with 0.1-μm film of modified cyclodextrin (CD) stationary phases. The preparation of columns included the investigation into the effect of the content of cyclodextrin derivative in polysiloxane, the type of polysiloxane and temperature of analysis on the quality of separation and retention of atropisomers of 15 selected PCB congeners. The separation properties towards PCBs of stationary phase heptakis(2,3-di-O-methyl-6-O-tert-butyl-dimethylsilyl)-β-CD dissolved in SE-30, SE-54, and OV-1701, were compared with those of 6-monokis-octamethylene-permethyl-β-CD anchored to polydimethylsiloxane polymer (ChirasilDex column, Chrompack, Middelburg, The Netherlands) and octakis(2,6-di-O-methyl-3-O-pentyl)-γ-CD in OV-1701 (MEGA, Legnano (MI), Italy). The correctness of quantitative enantiomer ratio determination was assesed by splitless analysis of PCBs reference solutions in concentration of 1.25–125 ng/ml (PCBs 45 and 91) and 2.5–250 ng/ml (PCB 95) (the PCB congeners are numbered according to IUPAC). Chirality 10:540–547, 1998. © 1998 Wiley-Liss, Inc.

A computer-assisted procedure was elaborated for optimization of selectivity of two capillary columns coupled in series for direct gas chromatographic multicomponent separations of enantiomers. Two fused-silica capillary columns (column A coated with permethyl-β-cyclodextrin (ChirasilDex) and column B coated with a mixture of heptakis(6-O-tert.-butyl-dimethylsilyl-2,3-O-diacetyl)-β-cyclodextrin and polysiloxane OV-1701 in 1:1 ratio (TBDMSDAC) were coupled in series via a T-piece. Each column was placed in an independently heated oven. Selectivity was tuned by variation of temperatures of the two columns (TA, TB) and carrier gas pressure in the column coupling point (pm) under a constant inlet and outlet pressure. The chromatograms were recorded under working conditions (TA, TB and pm) calculated using the Doehlert experimental design. Optimization procedure was based on mathematical models. A new threshold criterion for optimization of selectivity suitable for multicomponent sample separation was introduced. The elaborated optimization procedure was verified by separatingd- andl-enantiomers of N-trifluoroacetyl/O-alkyl derivatives of alanine, valine, 2-aminobutanoic acid and proline.

A simple dual-column gas chromatographic system,vith a six-port switching valve has been used to separate the atropisomers of PCB congeners 84, 91, and 95 in technical PCB formulations and in extracts of soil and river sediment. A capillary column coated with a methylphenylsiloxane stationary phase (CP-Sil 8) was used as the first column, for retention window selection, and a permethylated beta-cyclodextrin (ChirasilDex) capillary column as the main separation column, Because peak overlap could not be eliminated by optimization of column temperature, the enantiomeric ratios of PCB congeners could not be determined from the original chromatograms. The correct enantiomer ratio was determined from the peak areas obtained by deconvolution of the chromatograms, Whereas the PCB atropisomers considered were present in equal concentrations in the technical PCB formulations, analysis of a river sediment sample confirmed different residual concentrations of the atropisomers of congener 95.

The anaerobic degradation of PCB in loamy and clayey soils containing indigeneous microflora was studied. The anaerobic conditions were created by an argon atmosphere in the flasks containing soil flooded by a liquid medium with glucose. GC-ECD analysis of soil extracts after 40 day incubation showed, in addition to the concentration changes of the less chlorinated PCB congeners, a significant decrease in the concentration of highly chlorinated congeners in both soils. The results indicate that in both soil types reductive dehalogenation of PCB congeners was encountered.

The interconversion energy barriers and dipole moments of atropisomers of four polychlorinated biphenyls (PCB 91, PCB 95, PCB 132 and PCB 136) have been calculated with AM1 semiempirical quantum chemistry method. The rest of all molecular parameters were optimized prior to each energy and dipole moment calculations. The interconversion energy barriers found for some PCB by AM1 method, however, are substantially lower than those calculated from gas chromatographic data. This difference is proportional to intermolecular interactions of PCB atropisomers with a modified cyclodextrin stationary phase.

Kovats indices of cyclic and aromatic hydrocarbons, separated by capillary gas liquid chromatography on polydimethylsiloxane capillary columns, were found to increase with increasing stationary phase film thickness. This effect is explained in terms of adsorption of the stationary phase on the active sites of the inner surface of the capillary column. Since the number of active sites is limited, the overall polarity of the polydimethylsiloxane stationary phase is better defined in columns with thick stationary phase films. Interlaboratory reproducibility of retention indices of cyclic and aromatic hydrocarbons is therefore also better when using capillary columns with thick films of the polydimethylsiloxane stationary phase. Retention data obtained on such thick-film columns are influenced by adsorption of the stationary phase on the column walls to a lesser extent than in columns with thinner films.

Low-boiling secondary alcohols (2-butanol, 2-pentanol and 2- and 3-hexanol) and their methyl, pentyl, acetyl and trifluoroacetyl derivatives were separated by gas chromatography on a fused-sifica capillary column coated with a mixture of OV-1701 and heptakis (6-O-tert.-butyldimethylsilyl-2,3-di-O-acetyl)-β-cyclodextrin (1:1). The retention of these solutes was studied by determining their separation factors (α) and this temperature dependences. The retention of enantiomers was correlated with optical activity and structural data obtained by theoretical calculations. It was demonstrated that the separation of enantiomers on a modified cyclodextrin stationary phase is governed inter alia by total molecule asymmetries.

A novel threshold criterion based on the degree of peak overlap is proposed. It can be used for the evaluation of the degree of separation for simple or complex mixtures. The criterion considers quality of separation for relevant peaks only. Non-symmetrical peak shapes, different peak-height ratios and the influence of other peaks on the separation are also considered. The proposed criterion was tested on overlapped peaks of complex chromatograms obtained by capillary gas chromatography.

A porous carbon sorbent prepared by pyrolysis of cellulose in the presence of porogens was tested for the preconcentration of volatile organic pollutants (particularly hydrocarbons in the gasoline range) from water matrices by the purge-and-trap method. The trapped components were desorbed by carbon disulphide and measured by high-resolution capillary gas chromatography with on-column injection. The studied concentration range of individual hydrocarbons in water was 10 ppb-10 ppm. Drinking water, spring water and gasoline-contaminated water are given as examples of real sample analysis.

Ability to utilize a technical mixture of polychlorinated biphenyls (PCB), Delor 103, as the sole carbon source, has been tested in 14 bacterial strains. For the five best growing strains (Alcaligenes latus, Alcalgenes eutrophus, Comamonas testosteroni, Micrococcus varians and Pseudomonas putida), the dependence of the degradation of individual PCB congeners on the number of chlorine substituents is discussed.

A computer-assisted procedure is presented for optimization of selectivity of tandem capillary columns with the same apolar (SE-54) stationary phase by varying column temperatures. The procedure is based on a threshold criterion calculated from the required resolution factor in which the separating power of the columns as a function of temperature is incorporated. The validity of the procedure has been verified by the analysis of a sample containing 33 hydrocarbons on two 31 m×0.3 mm i.d. SE-54 capillary columns coupled in series and by varying the temperatures of both columns in the range 60–100°C. At the optimum temperatures (70°C for the first and 92°C for the second column) 26 compounds were resolved equal to or better than Rji=1.00 in 22.8 min.