Josef Planeta

Distribution of sulfur-containing aromatics between [hmim][Tf2N] and supercritical CO2: a case study for deep desulfurization of oil refinery streams by extraction with ionic liquids

Stringent regulations of the maximum content of sulfur in transportation fuels have prompted an intense search for new processes of deep desulfurization to complement common catalytic hydrodesulfurization. One of the alternative processes under development involves extraction of sulfur-containing aromatic compounds (SAs) from diesel fuel and gasoline with ionic liquids (ILs). In these applications, recycling of ILs will be highly important, and reextraction of SAs from ILs with supercritical carbon dioxide (scCO2) appears to be a possible method to regenerate ILs. The design and feasibility assessment of supercritical reextraction requires the partition coefficients of SAs between ILs and scCO2. We used open tubular capillary-column chromatography to measure the partition coefficients of several SAs between 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]) and scCO2, with [hmim][Tf2N] serving as the stationary liquid and scCO2 as the mobile phase (carrier fluid). The results confirm that the partition coefficients of SAs can be tuned within wide limits (over a decadic order of magnitude) by relatively modest changes in temperature (40–80 °C) and pressure (8.7–17.6 MPa). However, even the most favourable values of the partition coefficients of SAs between [hmim][Tf2N] and scCO2 suggest that feasibility of a large-scale supercritical reextraction process is questionable at best.

Polymethacrylate monolithic and hybrid particle-monolithic columns for reversed-phase and hydrophilic interaction capillary liquid chromatography.

We prepared hybrid particle-monolithic polymethacrylate columns for micro-HPLC by in situ polymerization in fused silica capillaries pre-packed with 3-5microm C(18) and aminopropyl silica bonded particles, using polymerization mixtures based on laurylmethacrylate-ethylene dimethacrylate (co)polymers for the reversed-phase (RP) mode and [2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl) zwitterionic (co)polymers for the hydrophilic interaction (HILIC) mode. The hybrid particle-monolithic columns showed reduced porosity and hold-up volumes, approximately 2-2.5 times lower in comparison to the pure monolithic columns prepared in the whole volume of empty capillaries. The elution volumes of sample compounds are also generally lower in comparison to packed or pure monolithic columns. The efficiency and permeability of the hybrid columns are intermediate in between the properties of the reference pure monolithic and particle-packed columns. The chemistries of the embedded solid particles and of the interparticle monolithic moiety in the hybrid capillary columns contribute to the retention to various degrees, affecting the selectivity of separation. Some hybrid columns provided improved separations of proteins in comparison to the reference particle-packed columns in the reversed-phase mode. Zwitterionic hybrid particle-monolithic columns show dual mode retention HILIC/RP behaviour depending on the composition of the mobile phase and allow separations of polar compounds such as phenolic acids in the HILIC mode at lower concentrations of acetonitrile and, often in shorter analysis time in comparison to particle-packed and full-volume monolithic columns.

Fitting adsorption isotherms to the distribution data determined using packed micro-columns for high-performance liquid chromatography

Knowing the adsorption isotherms of the components of a mixture on the chromatographic system used to separate them is necessary for a better understanding of the separation process and for the optimization of the production rate and costs in preparative high-performance liquid chromatography (HPLC). Currently, adsorption isotherms are usually measured by frontal analysis, using conventional analytical columns. Unfortunately, this approach requires relatively large quantities of pure compounds, and hence is expensive, especially in the case of pure enantiomers. In this work, we investigated the possible use of packed micro-bore and capillary HPLC columns for the determination of adsorption isotherms of benzophenone, o-cresol and phenol in reversed-phase systems and of the enantiomers of mandelic acid on a Teicoplanin chiral stationary phase. We found a reasonable agreement between the isotherm coefficients of the model compounds determined on micro-columns and on conventional analytical columns packed with the same material. Both frontal analysis and perturbation techniques could be used for this determination. The consumption of pure compounds needed to determine the isotherms decreases proportionally to the second power of the decrease in the column inner diameter, i.e. 10 times for a micro-bore column (1 mm I.D.) and 100 times for capillary columns (0.32 mm I.D.) with respect to 3.3 mm I.D. conventional columns.

Direct continuous supercritical fluid extraction as a novel method of wine analysis. Comparison with conventional indirect extraction and implications for wine variety identification.

Direct supercritical fluid extraction (SFE) of wines with carbon dioxide was compared to SFE of the sorbent used for solid-phase extraction of the same wine samples (SPE-SFE). Compared to SPE-SFE, the direct SFE results in amore specific and representative gas chromatographic fingerprint of the wine sample. The multivariate statistical processing of the direct SFE-GC data provides a clear-cut and sharp discrimination among the individual wine varieties while the discrimination based on the SPE-SFE-GC data is relatively poor. This finding reflects the adverse effects of additional analyte-sorbent interactions and sorption/desorption steps involved in SPE-SFE.

Zwitterionic silica-based monolithic capillary columns for isocratic and gradient hydrophilic interaction liquid chromatography

This study introduces zwitterionic monolithic capillary columns intended for isocratic and gradient HILIC separations. Silica-based monolithic capillary columns (100 μm × 150 mm) prepared by acidic hydrolysis of tetramethoxysilane in the presence of polyethylene glycol and urea were modified by a sulfoalkylbetaine zwitterion ([2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl)-ammonium hydroxide) to HILIC stationary phase. The prepared columns were evaluated under the isocratic and gradient separation conditions using a standard mixture containing nucleic acid bases, nucleosides, and 2-deoxynucleosides. Mobile phases contained high concentration of acetonitrile (95-85%, v/v) and 5-50mM ammonium acetate or ammonium formate in the pH range of 3-6. The synthesized columns showed a long-term stability under the separation conditions while the high permeability and efficiency originating from dual structure of the silica monolith were preserved. The relative standard deviations (RSDs) for the retention times of tested solutes were lower than 2% under the isocratic conditions and lower than 3.5% under the gradient conditions.

Separation of isomeric naphthalenesulphonic acids by micro high-performance liquid chromatography with mobile phases containing cyclodextrin

Aromatic sulphonic acids are important dye intermediates and the determination of the individual isomers after their preparation by sulphonation of the parent aromatic hydrocarbon is important for the monitoring of the dye production process. For this purpose, either reversed-phase chromatography with mobile phases containing strong electrolytes as additives or capillary zone electrophoresis with working electrolytes containing cyclodextrins can be used to separate and determine not only individual sulphonation products with various numbers of sulphonic groups, but also various isomeric di- and trisulphonic acids. However, the separation of some isomers using either of the two techniques is not fully satisfactory. In the present work, HPLC with mobile phases containing cyclodextrins was employed to improve previously achieved separations of aromatic sulphonic acids. Because of the high cost of cyclodextrin, microcolumn HPLC with diode-array detection on the columns prepared in laboratory by supercritical fluid packing technique was employed for this purpose. Capillary columns packed with various octadecyl silica gel materials were compared and their stability and efficiency were found suitable for the separation of the compounds tested. The selectivity of separation of some isomers improved significantly with respect to the previous methods. Procedures were designed for separation and analytical control of technological processes producing dye intermediates.

Separation of nucleobases, nucleosides, and nucleotides using two zwitterionic silica-based monolithic capillary columns coupled with tandem mass spectrometry.

The capability of employing synthesized zwitterionic silica-based monolithic capillary columns (140 mm × 0.1mm) for separation of highly polar and hydrophilic nucleobases, nucleosides, and nucleotides in hydrophilic interaction chromatography is reported. The suitability of the columns for on-line conjunction with electrospray tandem mass spectrometry was explored. Our results show that the grafted layer of zwitterionic monomer ([2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl)-ammonium hydroxide or 2-methacryloyloxyethyl phosphorylcholine) on the silica monolithic surface significantly improved the separation selectivity and reproducibility, as compared to the bare silica monolith. The stepwise elution from 90% to 70% of acetonitrile enabled separation of a complex sample mixture containing 21 compounds with a total analysis time less than 40 min.

Near- and supercritical water as a diameter manipulation and surface roughening agent in fused silica capillaries.

The prospects of near- and supercritical water for treatment of the inner surfaces of fused silica capillaries have been tested employing an in-lab-assembled apparatus. Unlike all other agents used for the purpose, water cannot introduce any undesirable heteroatoms to the treated surface. Theoretical background for this work comes from the well-known fact that water near its critical point can solubilize silica. The results show that depending on the temperature, water flow rate, flow mode, and exposure time, high-temperature water has wide-ranging effects on both the surface roughness and the internal diameter profile along the length of the treated capillary. By judicious selection of the operating conditions, tapered capillaries of various profiles for applications in electromigration techniques can be prepared with relatively high reproducibility. The water-treated fused silica capillaries with uniform internal diameter appear to be useful for preparation of monolithic silica capillary columns.

Silica-based monolithic capillary columns—Effect of preparation temperature on separation efficiency

The temperature effects during the sol-gel process and ageing of the silica-based monolith on the structure and separation efficiency of the capillary columns (100microm i.d., 150mm) for HPLC separations were studied. The tested columns were synthesized from a mixture of tetramethoxysilane, polyethylene glycol and urea under the acidic conditions. The temperature was varied from 40 degrees C to 44 degrees C and formation of bypass channels between the silica mold and the capillary wall was examined. The temperature of 43 degrees C was estimated as optimal for preparation of efficient silica capillary columns which were subsequently modified by octadecyldimethyl-N,N-diethylaminosilane or covered by poly(octadecyl methacrylate) and tested using standard mixture of alkylbenzenes under the isocratic conditions.

Distribution of Organic Solutes in Biphasic 1-n-Butyl-3-methylimidazolium Methyl Sulfate−Supercritical CO2 System

Interphase distribution of organic nonelectrolytes can be important in applications of biphasic solvent systems composed of a room-temperature ionic liquid and supercritical carbon dioxide (scCO(2)). Here, open tubular capillary-column supercritical fluid chromatography (SFC) with 1-n-butyl-3-methylimidazolium methyl sulfate ([bmim][MeSO(4)]) as the stationary liquid and scCO(2) as the carrier fluid was employed to measure retention factors of organic solutes within 313-353 K and 8.5-23.2 MPa. Solute selection included 18 compounds of diverse volatilities and chemical functionalities. The retention factors were converted to infinite-dilution solute partition coefficients in the biphasic [bmim][MeSO(4)]-scCO(2) system. At a constant temperature, an increase in scCO(2) density produced distinct shifts in relative retention (= separation factor), thus providing some pressure-tunable selectivity. At a particular temperature and density of CO(2), solute partition coefficients can be correlated in terms of linear solvation energy relationships. Analysis of the relative retention data by regular solution theory resulted in approximate values of the solubility parameter of CO(2)-expanded [bmim][MeSO(4)].